The term ripple factor is generally used in AC filter circuit design. The filtering process involves the conversion of pulsating DC voltage into a pure DC voltage wave. Pure DC voltage is required in several applications. The ripple factor shows the amount of AC component in the signal. More AC component means more ripples, which further leads to generate some noises. In very simple words, ripple factor is defined as the ratio of the RMS value (or the root mean square value) to the absolute value of the dc component in the output voltage. The ratio is expressed as a percentage, for the sake of convenience.
A rectifier converts AC into DC, but there will some AC particles and that is why the waveform will be a pulsating. But to generate pure DC, some filter circuit should be installed with the rectifier. And in this way the pulsating output of the rectifier is directly fed to the filter circuit in order to gain purely rectified dc output. The ac component is called the ripples. The ripple current is undesirable and its value should be the smallest possible to ensure the best performance.
Saturday, 5 July 2014
What is Form Factor?
The term form factor is particularly used in alternating current system. An alternating current waveform is sinusoidal in nature, so it has a peak value in positive and negative region both. But the average value of the signal is taken for the sake of convenience. Generally the form factor refers to the ratio of the RMS value (Root mean square value) to the average value of an AC signal waveform. For the same power, the value of direct current and alternating current is different from each other due to the phase sequence and sinusoidal behaviour of alternating waveform. So sometime it is needed to judge the quality of the AC voltage, and that is why form factor is used. It determines the ratio of the direct current with respect to the given alternating current for the same power.
The form factor is different for different types of AC waveform, that is square wave, sine wave, pulse wave etc. The concept is understandable by some other means. Suppose you have a coil and a DC source and an AC source. You connect the DC source with the coil and found that the coil is heated up after sometime, then when you connect the AC source with the coil and also found that the coil is heated up to that same level. But the amount of current is different for each sources. Since the RMS calculation is quite difficult in digital, therefore the average is determined the output is multiplied by the form factor of a sinusoid wave.
The form factor is different for different types of AC waveform, that is square wave, sine wave, pulse wave etc. The concept is understandable by some other means. Suppose you have a coil and a DC source and an AC source. You connect the DC source with the coil and found that the coil is heated up after sometime, then when you connect the AC source with the coil and also found that the coil is heated up to that same level. But the amount of current is different for each sources. Since the RMS calculation is quite difficult in digital, therefore the average is determined the output is multiplied by the form factor of a sinusoid wave.
What is IR LED?
An IR LED, is a special type of light emitting diode. It can transmit infra-red rays & the wavelength of those rays are typically 760 nanometre. IR LED's main construction material is gallium arsenide. But, sometime aluminium gallium arsenide also used as the main element of the IR LED.
In case of common LED, a glow is observed whenever a voltage difference is applied across the two terminals of it. You know, the human eye cannot see the infra-red rays, so it is not possible for a person to detect whether the IR LED is working or not.
To solve this problem, any type of camera can be used, because a camera can show us the IR rays.
A simple & daily application of IR LED is in our television remote. An IR LED is connected at the front side of any remote. IR LED also known as IR transmitter. IR LED & IR receivers combination is widely used in several sensor circuits.
In case of common LED, a glow is observed whenever a voltage difference is applied across the two terminals of it. You know, the human eye cannot see the infra-red rays, so it is not possible for a person to detect whether the IR LED is working or not.
To solve this problem, any type of camera can be used, because a camera can show us the IR rays.
A simple & daily application of IR LED is in our television remote. An IR LED is connected at the front side of any remote. IR LED also known as IR transmitter. IR LED & IR receivers combination is widely used in several sensor circuits.
What is tunnel diode?
In some electronic circuits, fast operation of diodes is desired. A tunnel diode is such kind of semiconductor diode which is known for its very fast and reliable operation. This diode is made by the use of the process called tunnelling.
The pn junction of these diodes is not so wider, but they are heavily doped. This specific connection helps to align the conduction electrons and valance holes. Electrons are the charge carrier, and acts as the majority carrier for tunnel diode. Highly doped pn region aligns the n region conduction electrons and p region valance holes. This process is called as tunnelling.
There are two kind of operation in tunnel diode. In forward bias operation the proper tunnelling operation is achieved. When the forward bias voltage starts increasing then the conduction electrons tunnel through the p-n junction barrier. In this way conduction electrons and valance holes get aligned with each other. If voltage is increasing again then the flowing current is decreasing which is called negative resistance. In reverse bias operation tunnel diode is called back diode. In this operation electrons tunnel through the p-n junction barrier but in the reverse direction. Mostly tunnel diodes are configured as forward bias mode, and after the increase of the forward bias voltage up to a level, it behaves like normal diode. Then the conducting electrons travels through the pn junction.
The pn junction of these diodes is not so wider, but they are heavily doped. This specific connection helps to align the conduction electrons and valance holes. Electrons are the charge carrier, and acts as the majority carrier for tunnel diode. Highly doped pn region aligns the n region conduction electrons and p region valance holes. This process is called as tunnelling.
There are two kind of operation in tunnel diode. In forward bias operation the proper tunnelling operation is achieved. When the forward bias voltage starts increasing then the conduction electrons tunnel through the p-n junction barrier. In this way conduction electrons and valance holes get aligned with each other. If voltage is increasing again then the flowing current is decreasing which is called negative resistance. In reverse bias operation tunnel diode is called back diode. In this operation electrons tunnel through the p-n junction barrier but in the reverse direction. Mostly tunnel diodes are configured as forward bias mode, and after the increase of the forward bias voltage up to a level, it behaves like normal diode. Then the conducting electrons travels through the pn junction.
Hysteresis Eddy Current Iron or Core Losses and Copper Loss in Transformer
As the electrical transformer is a static device, mechanical loss in transformer normally does not come into picture. We generally consider only electrical losses in transformer. Loss in any machine is broadly defined as difference between input power and output power.
When input power is supplied to the primary of transformer, some portion of that power is used to compensate core losses in transformer i.e. Hysteresis loss in transformer and Eddy current loss in transformer core and some portion of the input power is lost as I2R loss and dissipated as heat in the primary and secondary windings, because these windings have some internal resistance in them. The first one is called core loss or iron loss in transformer and the later is known as ohmic loss or copper loss in transformer. Another loss occurs in transformer, known as Stray Loss, due to Stray fluxes link with the mechanical structure and winding conductors.
Copper Loss in Transformer
Copper loss is I2R loss, in primary side it is I12R1 and in secondary side it is I22R2 loss, where I1 & I2 are primary & secondary current of transformer and R1 & R2 are resistances of primary & secondary winding. As the both primary & secondary currents depend upon load of transformer, copper loss in transformer vary with load.
Core Losses in Transformer
Hysteresis loss and eddy current loss, both depend upon magnetic properties of the materials used to construct the core of transformer and its design. So these losses in transformer are fixed and do not depend upon the load current. So core losses in transformer which is alternatively known as iron loss in transformer can be considered as constant for all range of load.
Hysteresis loss in transformer is denoted as,
Eddy current loss in transformer is denoted as,
Where, Kh = Hysteresis constant.
Ke = Eddy current constant.
Kf = form constant.
Copper loss can simply be denoted as,
IL2R2′ + Stray loss
Where, IL = I2 = load of transformer, and R2′ is the resistance of transformer referred to secondary.
Now we will discuss Hysteresis loss and Eddy current loss in little bit more details for better understanding the topic of losses in transformer
Hysteresis Loss in Transformer
Hysteresis loss in transformer can be explained in different ways. We will discuss two of them, one is physical explanation and the other is mathematical explanation.
Physical Explanation of Hysteresis Loss
The magnetic core of transformer is made of ′Cold Rolled Grain Oriented Silicon Steel′. Steel is very good ferromagnetic material. This kind of materials are very sensitive to be magnetized. That means, whenever magnetic flux would pass through, it will behave like magnet. Ferromagnetic substances have numbers of domains in their structure. Domains are very small regions in the material structure, where all the dipoles are paralleled to same direction. In other words, the domains are like small permanent magnets situated randomly in the structure of substance. These domains are arranged inside the material structure in such a random manner, that net resultant magnetic field of the said material is zero. Whenever external magnetic field or mmf is applied to that substance, these randomly directed domains get arranged themselves in parallel to the axis of applied mmf. After removing this external mmf, maximum numbers of domains again come to random positions, but some of them still remain in their changed position. Because of these unchanged domains, the substance becomes slightly magnetized permanently. This magnetism is called " Spontaneous Magnetism". To neutralize this magnetism, some opposite mmf is required to be applied. The magneto motive force or mmf applied in the transformer core is alternating. For every cycle due to this domain reversal, there will be extra work done. For this reason, there will be a consumption of electrical energy which is known as Hysteresis loss of transformer.
Mathematical Explanation of Hysteresis Loss in Transformer
Consider a ring of ferromagnetic specimen of circumference L meter, cross - sectional area a m2 and N turns of insulated wire as shown in the picture beside,
Let us consider, the electric current flowing through the coil is I amp,
Magnetizing force,
Let, the flux density at this instant is B,
Therefore, total flux through the ring, Φ = BXa Wb
As the electric current flowing through the solenoid is alternating, the flux produced in the iron ring is also alternating in nature, so the emf (e′) induced will be expressed as,
saturation curve of b - h curve
According to Lenz,s law this induced emf will oppose the flow of electric current, therefore, in order to maintain the current I in the coil, the source must supply an equal and opposite emf. Hence applied emf ,
Energy consumed in short time dt, during which the flux density has changed,
Thus, total work done or energy consumed during one complete cycle of magnetism,
Now aL is the volume of the ring and H.dB is the area of elementary strip of B - H curve shown in the figure above,
= total area enclosed by Hysteresis Loop.
Therefore, Energy consumed per cycle = volume of the ring X area of hysteresis loop.
In the case of transformer, this ring can be considered as magnetic core of transformer. Hence, the work done is nothing but the electrical energy loss in transformer core and this is known as hysteresis loss in transformer.
What is Eddy Current Loss ?
In transformer, we supply alternating current in the primary, this alternating current produces alternating magnetizing flux in the core and as this flux links with secondary winding, there will be induced voltage in secondary, resulting current to flow through the load connected with it. Some of the alternating fluxes of transformer; may also link with other conducting parts like steel core or iron body of transformer etc. As alternating flux links with these parts of transformer, there would be a locally induced emf. Due to these emfs, there would be currents which will circulate locally at that parts of the transformer. These circulating current will not contribute in output of the transformer and dissipated as heat. This type of energy loss is called eddy current loss of transformer.
When input power is supplied to the primary of transformer, some portion of that power is used to compensate core losses in transformer i.e. Hysteresis loss in transformer and Eddy current loss in transformer core and some portion of the input power is lost as I2R loss and dissipated as heat in the primary and secondary windings, because these windings have some internal resistance in them. The first one is called core loss or iron loss in transformer and the later is known as ohmic loss or copper loss in transformer. Another loss occurs in transformer, known as Stray Loss, due to Stray fluxes link with the mechanical structure and winding conductors.
Copper Loss in Transformer
Copper loss is I2R loss, in primary side it is I12R1 and in secondary side it is I22R2 loss, where I1 & I2 are primary & secondary current of transformer and R1 & R2 are resistances of primary & secondary winding. As the both primary & secondary currents depend upon load of transformer, copper loss in transformer vary with load.
Core Losses in Transformer
Hysteresis loss and eddy current loss, both depend upon magnetic properties of the materials used to construct the core of transformer and its design. So these losses in transformer are fixed and do not depend upon the load current. So core losses in transformer which is alternatively known as iron loss in transformer can be considered as constant for all range of load.
Hysteresis loss in transformer is denoted as,
Eddy current loss in transformer is denoted as,
Where, Kh = Hysteresis constant.
Ke = Eddy current constant.
Kf = form constant.
Copper loss can simply be denoted as,
IL2R2′ + Stray loss
Where, IL = I2 = load of transformer, and R2′ is the resistance of transformer referred to secondary.
Now we will discuss Hysteresis loss and Eddy current loss in little bit more details for better understanding the topic of losses in transformer
Hysteresis Loss in Transformer
Hysteresis loss in transformer can be explained in different ways. We will discuss two of them, one is physical explanation and the other is mathematical explanation.
Physical Explanation of Hysteresis Loss
The magnetic core of transformer is made of ′Cold Rolled Grain Oriented Silicon Steel′. Steel is very good ferromagnetic material. This kind of materials are very sensitive to be magnetized. That means, whenever magnetic flux would pass through, it will behave like magnet. Ferromagnetic substances have numbers of domains in their structure. Domains are very small regions in the material structure, where all the dipoles are paralleled to same direction. In other words, the domains are like small permanent magnets situated randomly in the structure of substance. These domains are arranged inside the material structure in such a random manner, that net resultant magnetic field of the said material is zero. Whenever external magnetic field or mmf is applied to that substance, these randomly directed domains get arranged themselves in parallel to the axis of applied mmf. After removing this external mmf, maximum numbers of domains again come to random positions, but some of them still remain in their changed position. Because of these unchanged domains, the substance becomes slightly magnetized permanently. This magnetism is called " Spontaneous Magnetism". To neutralize this magnetism, some opposite mmf is required to be applied. The magneto motive force or mmf applied in the transformer core is alternating. For every cycle due to this domain reversal, there will be extra work done. For this reason, there will be a consumption of electrical energy which is known as Hysteresis loss of transformer.
Mathematical Explanation of Hysteresis Loss in Transformer
Consider a ring of ferromagnetic specimen of circumference L meter, cross - sectional area a m2 and N turns of insulated wire as shown in the picture beside,
Let us consider, the electric current flowing through the coil is I amp,
Magnetizing force,
Let, the flux density at this instant is B,
Therefore, total flux through the ring, Φ = BXa Wb
As the electric current flowing through the solenoid is alternating, the flux produced in the iron ring is also alternating in nature, so the emf (e′) induced will be expressed as,
saturation curve of b - h curve
According to Lenz,s law this induced emf will oppose the flow of electric current, therefore, in order to maintain the current I in the coil, the source must supply an equal and opposite emf. Hence applied emf ,
Energy consumed in short time dt, during which the flux density has changed,
Thus, total work done or energy consumed during one complete cycle of magnetism,
Now aL is the volume of the ring and H.dB is the area of elementary strip of B - H curve shown in the figure above,
= total area enclosed by Hysteresis Loop.
Therefore, Energy consumed per cycle = volume of the ring X area of hysteresis loop.
In the case of transformer, this ring can be considered as magnetic core of transformer. Hence, the work done is nothing but the electrical energy loss in transformer core and this is known as hysteresis loss in transformer.
What is Eddy Current Loss ?
In transformer, we supply alternating current in the primary, this alternating current produces alternating magnetizing flux in the core and as this flux links with secondary winding, there will be induced voltage in secondary, resulting current to flow through the load connected with it. Some of the alternating fluxes of transformer; may also link with other conducting parts like steel core or iron body of transformer etc. As alternating flux links with these parts of transformer, there would be a locally induced emf. Due to these emfs, there would be currents which will circulate locally at that parts of the transformer. These circulating current will not contribute in output of the transformer and dissipated as heat. This type of energy loss is called eddy current loss of transformer.
What is boolean algebra?
Today digital circuits and modern computers play a very important role in our day to day life. Boolean logic or digital logic is the foundation of these modern digital computers. Boolean algebra is used to analyze and simplify these digital circuits. Boolean Algebra was developed by George Boole in the mid 1800's.
Boolean algebra use's the binary number system i.e 1's and 0's. Variables used in boolean algebra can have only two values, binary 1 for (HIGH or TRUE) and binary 0 for (LOW or FALSE). In boolean algebra everything is in terms of 0's and 1's only.
Example : 1 for the switch is on & 0 for the switch is off , 1 for current is 20 mA & 0 for the current is 2 mA. The rules of boolean algebra are different from those used in our conventional algebra. There are no negative numbers, fractions, square root, logarithm, squares etc. Arithmetic operations like addition, subtraction, multiplications etc. are not performed in boolean algebra.
Boolean algebra use's the binary number system i.e 1's and 0's. Variables used in boolean algebra can have only two values, binary 1 for (HIGH or TRUE) and binary 0 for (LOW or FALSE). In boolean algebra everything is in terms of 0's and 1's only.
Example : 1 for the switch is on & 0 for the switch is off , 1 for current is 20 mA & 0 for the current is 2 mA. The rules of boolean algebra are different from those used in our conventional algebra. There are no negative numbers, fractions, square root, logarithm, squares etc. Arithmetic operations like addition, subtraction, multiplications etc. are not performed in boolean algebra.
What are the uses of microprocessors?
Microprocessor is an electronic circuit that is based on integrated chip IC. Microprocessor has all the functions of a Central processing Unit (CPU) of a computer. It either used single chip for that or multiple chips are also used. Microprocessors are a multi-purpose device. It performs three functions – accepts digital data as input, processes the data and stores it in the storage devices – registers and gives the output. First commercial microprocessor was developed by Intel in 1960's and it was a 4 bit microprocessor. Microprocessor performs with three main steps fetch, decode and execute methods. Use of microprocessor is not limited to a particular area instead it is has diverse applications. They include small and large scale applications. Some of them are discussed below:
Used in cars that is in its accessory parts, in toys, test instruments, computers.
Finds applications in electrical circuit breakers, switches, smoke alarm battery, radio.
Devices like – DVD player, cell phones other audio-visual components use microprocessors.
Broadcast systems, satellite communication, automotive, home security systems also use microprocessor.
Also used in washing machines, i-pod, remote control and other electronic devices.
Microprocessors are ICs so they find applications in household items like refrigerator, microwave ovens, cell phones , others.
Aerospace vehicles , nuclear reactors and also in some instruments like – function generators, frequency counter and spectrum analyzers.
Digital cameras, lifts, remote control cars, games console, traffic light system all uses microprocessors for their functioning.
Used in cars that is in its accessory parts, in toys, test instruments, computers.
Finds applications in electrical circuit breakers, switches, smoke alarm battery, radio.
Devices like – DVD player, cell phones other audio-visual components use microprocessors.
Broadcast systems, satellite communication, automotive, home security systems also use microprocessor.
Also used in washing machines, i-pod, remote control and other electronic devices.
Microprocessors are ICs so they find applications in household items like refrigerator, microwave ovens, cell phones , others.
Aerospace vehicles , nuclear reactors and also in some instruments like – function generators, frequency counter and spectrum analyzers.
Digital cameras, lifts, remote control cars, games console, traffic light system all uses microprocessors for their functioning.
What is Microprocessor?
A microprocessor incorporates the functions of a computer's central processing unit (CPU) on a single integrated circuit (IC),or at most a few integrated circuits. It is a multi-purpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and provides results as output. It is an example of sequentiality digital logic, as it has internal memory. Microprocessors operate on numbers and symbols represented in the binary numeral system. The advent of low-cost computers on integrated circuits has transformed modern society. General-purpose microprocessors in personal computers are used for computation, text editing, multimedia display, and communication over the Internet. Many more microprocessors are part of embedded systems, providing digital control over myriad objects from appliances to auto mobiles to cellular phones and industrial process control.
The internal arrangement of a microprocessor varies depending on the age of the design and the intended purposes of the processor. The complexity of an integrated circuit is bounded by physical limitations of the number of transistors that can be put onto one chip, the number of package terminations that can connect the processor to other parts of the system, the number of interconnections it is possible to make on the chip, and the heat that the chip can dissipate. Advancing technology makes more complex and powerful chips feasible to manufacture.
A minimal hypothetical microprocessor might only include an arithmetic logic unit (ALU) and a control logic section. The ALU performs operations such as addition, subtraction, and operations such as AND or OR. Each operation of the ALU sets one or more flags in a status register, which indicate the results of the last operation (zero value, negative number, overflow. or others). The logic section retrieves instruction operation codes from memory, and initiates whatever sequence of operations of the ALU requires to carry out the instruction. A single operation code might affect many individual data paths, registers, and other elements of the processor.
As integrated circuit technology advanced, it was feasible to manufacture more and more complex processors on a single chip. The size of data objects became larger; allowing more transistors on a chip allowed word sizes to increase from 4 and 8-bit words up to today's 64-bit words. Additional features were added to the processor architecture; more on-chip registers sped up programs, and complex instructions could be used to make more compact programs. Floating-point arithmetic, for example, was often not available on 8-bit microprocessors, but had to be carried out in software.
Integration of the floating point unit first as a separate integrated circuit and then as part of the same microprocessor chip, sped up floating point calculations. Occasionally, physical limitations of integrated circuits made such practices as a bit slice approach necessary. Instead of processing all of a long word on one integrated circuit, multiple circuits in parallel processed subsets of each data word. While this required extra logic to handle, for example, carry and overflow within each slice, the result was a system that could handle, say, 32-bit words using integrated circuits with a capacity for only 4 bits each.
With the ability to put large numbers of transistors on one chip, it becomes feasible to integrate memory on the same die as the processor. This CPU cache has the advantage of faster access than off-chip memory, and increases the processing speed of the system for many applications. Generally, processor speed has increased more rapidly than external memory speed, so cache memory is necessary if the processor is not delayed by slower external memory.
The internal arrangement of a microprocessor varies depending on the age of the design and the intended purposes of the processor. The complexity of an integrated circuit is bounded by physical limitations of the number of transistors that can be put onto one chip, the number of package terminations that can connect the processor to other parts of the system, the number of interconnections it is possible to make on the chip, and the heat that the chip can dissipate. Advancing technology makes more complex and powerful chips feasible to manufacture.
A minimal hypothetical microprocessor might only include an arithmetic logic unit (ALU) and a control logic section. The ALU performs operations such as addition, subtraction, and operations such as AND or OR. Each operation of the ALU sets one or more flags in a status register, which indicate the results of the last operation (zero value, negative number, overflow. or others). The logic section retrieves instruction operation codes from memory, and initiates whatever sequence of operations of the ALU requires to carry out the instruction. A single operation code might affect many individual data paths, registers, and other elements of the processor.
As integrated circuit technology advanced, it was feasible to manufacture more and more complex processors on a single chip. The size of data objects became larger; allowing more transistors on a chip allowed word sizes to increase from 4 and 8-bit words up to today's 64-bit words. Additional features were added to the processor architecture; more on-chip registers sped up programs, and complex instructions could be used to make more compact programs. Floating-point arithmetic, for example, was often not available on 8-bit microprocessors, but had to be carried out in software.
Integration of the floating point unit first as a separate integrated circuit and then as part of the same microprocessor chip, sped up floating point calculations. Occasionally, physical limitations of integrated circuits made such practices as a bit slice approach necessary. Instead of processing all of a long word on one integrated circuit, multiple circuits in parallel processed subsets of each data word. While this required extra logic to handle, for example, carry and overflow within each slice, the result was a system that could handle, say, 32-bit words using integrated circuits with a capacity for only 4 bits each.
With the ability to put large numbers of transistors on one chip, it becomes feasible to integrate memory on the same die as the processor. This CPU cache has the advantage of faster access than off-chip memory, and increases the processing speed of the system for many applications. Generally, processor speed has increased more rapidly than external memory speed, so cache memory is necessary if the processor is not delayed by slower external memory.
How does antenna work?
Antenna is a electrical device that converts radio-frequency into alternating current. It is used to send or receive electromagnetic waves. Radio antennas have two fold functions. The first of this functions is to radiate the radio frequency energy generated in the transmitter and fed to the antenna by a transmission line. In this capacity the antenna acts as an impedance matching device to match the impedance of the transmission line to that of free space. The other function of the antenna is to direct the energy into desired directions and as suppress to the radiation in unwanted directions.
A completely non-directional or omni-directional radiator radiates uniformly in all directions and is known as isotropic radiator. A point source of sound is an example of an isotropic radiator. the radiation pattern of an antenna is a graphical representation of the radiation of the antenna as a function of direction. If the radiation is expressed as field strength per meter the radiation pattern is field strength pattern. If the radiation in a given direction is expressed in terms of power per unit solid angle , the resulting pattern is power pattern. The co-ordinate system generally used in the specification of antenna radiation pattern is the spherical co-ordinate system. The antenna is locked at or near the origin of this system and the field strength is specified at points on the spherical surface or surface radius. The shape of the radiation pattern is independent of surface radius If the surface radius is chosen sufficiently large. When this is true, the magnitude of the field strength in any direction varies inversely with surface radius and so needs to be stated for only one value of surface radius.for example, in broadcast antenna works, it is customary to state the field strength at a radius of one mile or one kilometre. Often only the relative radiation pattern is used. This gives the relative field strengths in various directions, usually referred to unity in the direction of maximum radiation.
A completely non-directional or omni-directional radiator radiates uniformly in all directions and is known as isotropic radiator. A point source of sound is an example of an isotropic radiator. the radiation pattern of an antenna is a graphical representation of the radiation of the antenna as a function of direction. If the radiation is expressed as field strength per meter the radiation pattern is field strength pattern. If the radiation in a given direction is expressed in terms of power per unit solid angle , the resulting pattern is power pattern. The co-ordinate system generally used in the specification of antenna radiation pattern is the spherical co-ordinate system. The antenna is locked at or near the origin of this system and the field strength is specified at points on the spherical surface or surface radius. The shape of the radiation pattern is independent of surface radius If the surface radius is chosen sufficiently large. When this is true, the magnitude of the field strength in any direction varies inversely with surface radius and so needs to be stated for only one value of surface radius.for example, in broadcast antenna works, it is customary to state the field strength at a radius of one mile or one kilometre. Often only the relative radiation pattern is used. This gives the relative field strengths in various directions, usually referred to unity in the direction of maximum radiation.
What is lightning arrestor ?
Lightning arrestor is a device which is mainly installed across each phase and earth at the entry of the transmission line to the sub - station yard. It can also be seen at HV and LV sides of all power transformer installed at the sub - station. The modern LA is generally made of gap less ZnO. In this type of Lightning Arrestor required number of ZnO or zinc oxide discs are kept inside a hollow cylinder of insulated material such as porcelain. The column of ZnO discs is kept under spring pressure at its top or bottom under the hollow cylinder to ensure no gap between the discs in the column.
ZnO has such a property that it behaves as short circuit during transient surge over voltage and over frequency of the power system and becomes like normal insulator when transient surge voltage is over. So when lightning strikes on the overhead transmission line, the over voltage impulse travel toward both ends of the line and bypasses through the lightning arrestor to ground at the entry of the sub - station. As the transformer is the costliest equipment installed in the system, for better protection of each transformer is equipped with lightning arrestor at its both HV and LV sides.
ZnO has such a property that it behaves as short circuit during transient surge over voltage and over frequency of the power system and becomes like normal insulator when transient surge voltage is over. So when lightning strikes on the overhead transmission line, the over voltage impulse travel toward both ends of the line and bypasses through the lightning arrestor to ground at the entry of the sub - station. As the transformer is the costliest equipment installed in the system, for better protection of each transformer is equipped with lightning arrestor at its both HV and LV sides.
Difference between VCB and SF6 circuit breaker.
In VCB or vacuum circuit breakers vacuum is used for arc quenching. The contacts of the breaker are kept in vacuum inside an airtight chamber. There is no air to sustain the arc. During the opening of the contacts the metal is vaporized which helps to sustain the arc for the first cycle but when the current reaches zero the vapour turns back into solid and the arc cannot sustain.
On the other hand in SF6 circuit breakers SF6 gas is used as the insulating medium. SF6 gas has very high dielectric strength, high electro negativity (which helps to absorb the electrons from the arc), high thermal stability. The SF6 gas is made to run around the contacts axially when the arc is formed and hence quenching the arc rapidly.
On the other hand in SF6 circuit breakers SF6 gas is used as the insulating medium. SF6 gas has very high dielectric strength, high electro negativity (which helps to absorb the electrons from the arc), high thermal stability. The SF6 gas is made to run around the contacts axially when the arc is formed and hence quenching the arc rapidly.
What is SF6 Circuit Breaker ?
A circuit breaker is a device used in electrical power system for breaking or making of a network. This is required when there is a maintenance work needed or when there occurs a fault in the network. For the second case the circuit breaker operates automatically when the relay coil trips. During the operation of a circuit breaker an arc is formed when the contacts move away from each other. To quench this arc different dielectric mediums of high dielectric strengths are used. The most common insulating medium used in the circuit breakers is SF6 gas.
The contacts are kept in a chamber filled with SF6 gas at high pressure (may be up to 14kg/m2). SF6 gas is very useful for quenching the arc for its high dielectric strength and electro negativity. This types of circuit breakers are called SF6 circuit breaker.
The contacts are kept in a chamber filled with SF6 gas at high pressure (may be up to 14kg/m2). SF6 gas is very useful for quenching the arc for its high dielectric strength and electro negativity. This types of circuit breakers are called SF6 circuit breaker.
What is ferranti effect ?
In general when the receiving end voltage is greater than the sending end voltage then that is called Ferranti effect.
It is mainly a part of transmission line. When a transmission line is lightly loaded or not loaded, then the receiving end voltage exceeds the sending end voltage. The loads are normally inductive in nature, which draws a huge amount of reactive power. Typically capacitors are connected in parallel to the transmission lines to supply this reactive power but when the transmission lines are not loaded or lightly loaded, the reactive power supplied by the capacitors adds on to the transmission line and as a result the receiving end voltage is found to be greater than the sending end voltage which is termed as Ferranti effect.
Ferranti Effect on Transmission Lines
Power triangle describes the relationship between real power and reactive power. Real power is the power, which flows through the circuit without being stored or interrupted. Reactive power is that power which is stored in the circuit for some time and the power returns to the source in each cycle. Now returning to the transmission lines, the loads connected with the transmission lines are inductive in nature and they require reactive power. To introduce reactive power in to the circuit, the angle between real power and apparent power is increased or power factor is reduced. To do this, capacitors are connected in parallel with the transmission lines which store energy in one cycle and release in the other cycle, hence fulfilling the requirement of the reactive power. But when the transmission line is at no load or lightly loaded condition there is excess reactive power in the network which is added with the real power and at the receiving end we get more voltage than the supply end voltage, this phenomenon is termed as Ferranti effect. So in a single sentence Ferranti effect can be understood as the incidence when the receiving end voltage is greater than the sending end voltage.
Causes of the Ferranti Effect
Loads can be divided in three types: resistive load, capacitive load and capacitive load. Normally we are familiar with resistive loads but most of the loads connected with the transmission lines are inductive in nature. So the power requirement changes in to two type’s-
• Resistive or real power.
• Reactive (capacitive/inductive) power.
Power generated by the power plants supplies the actual power through the transmission lines. So, to get the required reactive power some steps are taken and some changes are made in the transmission lines. The most common of them is the power factor correction. The power factor can be corrected by introducing capacitors in parallel with the transmission lines. These capacitors will supply the required reactive power to the network. Now suppose the transmission lines are at no load or in very lightly loaded condition. Then reactive power requirement is zero or very low but the capacitors keep on supplying reactive power which will be added on to the transmission lines and ultimately increasing the receiving end voltage. The term Ferranti effect describes the phenomenon when the receiving end voltage is greater than the sending end voltage.
Hence the main cause of this phenomenon is when the transmission line is at no load or lightly loaded condition and then the receiving end voltage is higher.
What is electrical load?
Current flows through a circuit only when it is closed. So, to get a steady flow of current loads are needed to be connected at the terminals of the circuit. Without the load the circuit is said to be open circuited.
If the circuit is completed without connecting the load the circuit is termed to be at short circuited condition the current flow is very huge at the point which can damage the circuit. Load is nothing but impedance. There are several types of loads present depending on their nature which are listed below.
According to load nature
According to load function
According to load consumer category
According to load grouping
According to load planning
According to load operation time
According to load/phase distribution
According to number of electrical loads phases
According to electrical loads usage method
According to method of load reduction /control
If the circuit is completed without connecting the load the circuit is termed to be at short circuited condition the current flow is very huge at the point which can damage the circuit. Load is nothing but impedance. There are several types of loads present depending on their nature which are listed below.
According to load nature
- Resistive electrical loads
- Capacitive electrical loads
- Inductive electrical loads
- Combination electrical loads
According to load function
- Lightning load
- Small appliances load
- Power loads
According to load consumer category
- Residential electrical loads
- Commercial electrical loads
- Industrial electrical load
- Traction loads
According to load grouping
- Industrial loads
- Load center
According to load planning
- Existing electrical loads
- Future electrical loads
- New electrical loads
According to load operation time
- Continuous electrical loads
- Non- continuous electrical loads
- Duty intermittent electrical loads
- Duty periodic electrical loads
- Duty short time electrical loads
According to load/phase distribution
- Balanced electrical loads
- Non-balanced electrical loads
- Neutral loads
- Line to neutral load
According to number of electrical loads phases
- Single phase electrical loads
- Three phase electrical loads
According to electrical loads usage method
- Fixed place loads
- Portable loads
According to method of load reduction /control
- Dimmed electrical load
- Shed electrical load
- Shifted electrical load.
What is LVDT?
LVDT or Linear variable differential transformer is a passive transducer and is commonly employed to measure force (or weight, pressure and acceleration etc. which depend on force) in terms of the amount and direction of displacement of an object.
Construction :
It consists of one primary and two secondary windings S1 and S2. These are place on either side of the primary mounted on the same magnetic core. The magnetic core is free to move axially inside the coil assembly and the motion being measured is mechanically coupled to it. The two secondary winding have equal number of turns but are connected in series opposition. Emf induced in them are 180° out of phase. The primary is fed form an a.c source.
Working Principle:
When the core is in the centre (reference position) and induced voltages E1 and E2are equal and opposite. Hence they cancel out and output voltage is zero. When the external applied force moves the core towards coil S2, E2 is increased but E1 is decreased in magnitude though they are still anti phase with each other. The net voltage available is (E2 - E1) is in phase with E2.
Construction :
It consists of one primary and two secondary windings S1 and S2. These are place on either side of the primary mounted on the same magnetic core. The magnetic core is free to move axially inside the coil assembly and the motion being measured is mechanically coupled to it. The two secondary winding have equal number of turns but are connected in series opposition. Emf induced in them are 180° out of phase. The primary is fed form an a.c source.
Working Principle:
When the core is in the centre (reference position) and induced voltages E1 and E2are equal and opposite. Hence they cancel out and output voltage is zero. When the external applied force moves the core towards coil S2, E2 is increased but E1 is decreased in magnitude though they are still anti phase with each other. The net voltage available is (E2 - E1) is in phase with E2.
What is an autotransformer?
An auto transformer is a special type of electrical transformer with only one winding on an iron core. In auto transformer, one single winding is used as primary winding as well as secondary winding.
The winding ab of total turns N1 is considered as primary winding.
This winding is tapped from point c and the portion bc is considered as secondary. Let’s assume that the number of turns in between points B and C is N2. If V1 voltage is applied across the primary winding i.e. in between A and B. So voltage per turn in this winding is V1 / N1
Hence, the voltage across the portion bc that is the secondary, will be V1N2 /N1 and this voltage is V2.
Hence, V1N2 / N1 = V2
⇒ V2 / V1 = N2 / N1 = Constant = k
As BC portion of the winding is considered as secondary, it can easily be understood that value of constant k is nothing but turns ratio or the voltage ratio of that autotransformer.
Uses of an autotransformer
Power distribution : Auto transformers are frequently used in power applications to interconnect systems operating at different voltage levels, such as to 66 kV to 138 kV transmission line.
Another use of auto transformer is in industry to adapt machinery built for 480 V supplies to operate on a 600 V supply.
Auto transformers are also used for providing conversions in between the two common main voltage bands in the area
(suppose 100 to 130 and 200 to 250).
In long power distribution lines, special auto transformers equipped with automatic tap-changer are inserted as voltage regulators. Thus, customers at the far voltage source.
A special type of auto transformer is used to provide grounding on three-phase systems.
Tapped auto transformers are frequently used to match impedance, eg: they are inserted in between a low-impedance microphone and a high-impedance amplifier input.
The winding ab of total turns N1 is considered as primary winding.
This winding is tapped from point c and the portion bc is considered as secondary. Let’s assume that the number of turns in between points B and C is N2. If V1 voltage is applied across the primary winding i.e. in between A and B. So voltage per turn in this winding is V1 / N1
Hence, the voltage across the portion bc that is the secondary, will be V1N2 /N1 and this voltage is V2.
Hence, V1N2 / N1 = V2
⇒ V2 / V1 = N2 / N1 = Constant = k
As BC portion of the winding is considered as secondary, it can easily be understood that value of constant k is nothing but turns ratio or the voltage ratio of that autotransformer.
Uses of an autotransformer
Power distribution : Auto transformers are frequently used in power applications to interconnect systems operating at different voltage levels, such as to 66 kV to 138 kV transmission line.
Another use of auto transformer is in industry to adapt machinery built for 480 V supplies to operate on a 600 V supply.
Auto transformers are also used for providing conversions in between the two common main voltage bands in the area
(suppose 100 to 130 and 200 to 250).
In long power distribution lines, special auto transformers equipped with automatic tap-changer are inserted as voltage regulators. Thus, customers at the far voltage source.
A special type of auto transformer is used to provide grounding on three-phase systems.
Tapped auto transformers are frequently used to match impedance, eg: they are inserted in between a low-impedance microphone and a high-impedance amplifier input.
What is Buchholz Relay?
Actually, any types of relay is used to protection purpose but the main objective of a relay is to sense the excess current flow in the circuit and depends upon the intensity of the current flow the relay trips and the circuit breaker is closed. Therefore the faulted part of the circuit is isolated from the healthy network. Now Buchhloz's relay is a special type of relay which is used only in the transformer tanks and unlike being activated by the excess current voltage, it trips by the gases formed. Whenever any fault take place in the transformer, the oil decomposes and various chemical reactions take place and several gases are formed. Using the intensity of gas production, Buchholz's relay operated. There are two hinged flow situated in the middle chamber. The lower one is connected with the circuit breaker and the upper one initiates a signal or alarm.
When the fault is minor, the rate of production of gas is low and therefore the force induced by them is also low which don’t tilt the lower hing but stored in the upper part of the chamber. As soon as the amount of the gases increased, it tilts the upper hing which initiates a signal and the alarm goes off, which indicates that there is something wrong in the transformer. But when the fault is severe the rate of production of gas is pretty high which is able to tilt the lower hing and as a result the contacts of the circuit breaker is closed and the transformer circuit is tripped.
When the fault is minor, the rate of production of gas is low and therefore the force induced by them is also low which don’t tilt the lower hing but stored in the upper part of the chamber. As soon as the amount of the gases increased, it tilts the upper hing which initiates a signal and the alarm goes off, which indicates that there is something wrong in the transformer. But when the fault is severe the rate of production of gas is pretty high which is able to tilt the lower hing and as a result the contacts of the circuit breaker is closed and the transformer circuit is tripped.
What is Magnetizing Current ?
Magnetizing current is a current component which is seen in electrical machines likes transformers and motors. No load current of transformer has two components, one is the magnetizing component and other is the active component.
Magnetizing component is also called the reactive or wattles component of no-load current. The active component or watt full component supplies the hysteresis and eddy current loses. Magnetizing component of no load current magnetizes the core of the transformer. Thus this component sets up flux in the transformer core.
Magnetizing current is in phase with the flux and is 90 ° to applied voltage and active component. Magnetizing current is associated with the primary winding of the transformer. It is the current that flows in primary when voltage is applied across it and in this condition secondary is unloaded. Magnetizing current value is related to supply voltage, frequency and primary inductance value. Primary side always has a current irrespective of the load condition of transformer which is called magnetizing current and this current adds on to the load current. So primary of transformer draws a peak current that is known as magnetizing inrush current. Magnitude of this current is high and it lasts for a very less time and it is transient in nature.
Magnetizing component is also called the reactive or wattles component of no-load current. The active component or watt full component supplies the hysteresis and eddy current loses. Magnetizing component of no load current magnetizes the core of the transformer. Thus this component sets up flux in the transformer core.
Magnetizing current is in phase with the flux and is 90 ° to applied voltage and active component. Magnetizing current is associated with the primary winding of the transformer. It is the current that flows in primary when voltage is applied across it and in this condition secondary is unloaded. Magnetizing current value is related to supply voltage, frequency and primary inductance value. Primary side always has a current irrespective of the load condition of transformer which is called magnetizing current and this current adds on to the load current. So primary of transformer draws a peak current that is known as magnetizing inrush current. Magnitude of this current is high and it lasts for a very less time and it is transient in nature.
How a synchronous motor starts?
Synchronous speed is referred as the speed of the rotating flux. So, as the name suggests a motor which rotates at synchronous speed is synchronous motor. Synchronous motors run at the same speed as that of the rotating flux. The speciality of a synchronous motor is that the starter is connected with 3 phase supply and the rotor is connected with dc supply to make it a permanent magnet.
Now when 3 phase supply is given to the motor there is a rotating flux generated, which rotates at the synchronous speed. Now the rotor which is a magnet which is not rotated automatically, or it can be said that the synchronous motor is not self starting. The reason behind that the rotating flux rotates at very high speed. So, the poles of the rotor can not get locked with the stator poles and the motor does not works. To start the operation of the synchronous motor the rotor is first rotated by an external prime mover or a separate motor. The main aim for doing this is to reduce the speed difference between the rotating flux and rotor poles. When the relative speed between these two almost reaches zero, the poles of the rotor gets attached or locked with the flux. In this way, the rotor starts to rotate at synchronous speed.
Another method of starting of synchronous motor is by using damper windings. In this case at first the supply (dc) to the rotor is switched off and the motor starts to rotate on the principle of squirrel cage induction motor. When the relative speed between the rotor and the rotating flux decreases the rotor is energized by dc supply and the rotor gets locked with flux and starts to rotate at synchronous speed.
Now when 3 phase supply is given to the motor there is a rotating flux generated, which rotates at the synchronous speed. Now the rotor which is a magnet which is not rotated automatically, or it can be said that the synchronous motor is not self starting. The reason behind that the rotating flux rotates at very high speed. So, the poles of the rotor can not get locked with the stator poles and the motor does not works. To start the operation of the synchronous motor the rotor is first rotated by an external prime mover or a separate motor. The main aim for doing this is to reduce the speed difference between the rotating flux and rotor poles. When the relative speed between these two almost reaches zero, the poles of the rotor gets attached or locked with the flux. In this way, the rotor starts to rotate at synchronous speed.
Another method of starting of synchronous motor is by using damper windings. In this case at first the supply (dc) to the rotor is switched off and the motor starts to rotate on the principle of squirrel cage induction motor. When the relative speed between the rotor and the rotating flux decreases the rotor is energized by dc supply and the rotor gets locked with flux and starts to rotate at synchronous speed.
What is the speed regulation of a dc motor?
Suppose a dc motor is running at no load. That means no conveyor belt or any other type of gear fitted with the shaft of the motor and the shaft is free to rotate. Now assume the load is put on the shaft by means of conveyor belt or gear etc. After applying the load there may be a change of speed of the motor. The term speed regulation refers to the change in speed of a motor with change in applied load.
The speed regulation is defined as the change in speed when the load on the motor is reduced from rated value to zero, expressed as percent of the rated load speed.
The speed at which the motor rotates when no load is applied to the rotor shaft is referred as no load speed.
The speed, at which the motor rotates when full rated load is applied to the motor shaft, is referred as full load speed.
Now speed regulation of dc motor is referred as the difference of no load speed and full load speed expressed as percentage of full load speed.
The speed regulation is defined as the change in speed when the load on the motor is reduced from rated value to zero, expressed as percent of the rated load speed.
The speed at which the motor rotates when no load is applied to the rotor shaft is referred as no load speed.
The speed, at which the motor rotates when full rated load is applied to the motor shaft, is referred as full load speed.
Now speed regulation of dc motor is referred as the difference of no load speed and full load speed expressed as percentage of full load speed.
What is back emf in dc motor ?
When current is flowing through the armature conductor of dc motor, it starts rotating inside the magnetic field of stator pole. As the armature conductors move inside the magnetic field there will be an induced emf in the armature conductor. This emf would be due to Faraday law of electromagnetic induction. The direction of the induced emf will be as per Fleming right hand rule and the induced emf will oppose the applied voltage across the armature terminals. In other words in dc motor the rotating armature will generate an emf as it is rotating under magnetic field, in opposite of the applied voltage and this generated emf in dc motor is called back emf.
How DC Motor works ?
Electrical machines can be divided into two types depending upon the type of current they are supplied, these are ac machines and dc machines. Now in case of dc machines the two type of machines, which are used widely are dc generators and dc motors. In every rotating electrical machine there are two parts, stator and rotor. For dc motors the field wielding is connected with the stator and the armature winding is connected with the rotor part of the motor.
dc shunt motor
For dc motor there is a field connected in parallel or series with the dc motor. Depending on this there are three types of dc motor series motor (where field is connected in series with the motor), shunt motor (where the field is in parallel with the motor) another type of motor is compound motor where series and shunt field both are present in the motor.
Now the main working principle of any dc motor is mainly due to electromagnetic phenomenon, the above mentioned field acts as permanent magnet. The current through the field I flows which marks it a permanent magnet. Now V terminal applied to the motor. We know that where current flows through circuit and that circuit is present inside a magnetic field then there is a torque produced, which is directed towards depending upon the face of the permanent magnets. Same case goes on with dc motors. When V is applied the rotor starts to rotate and then after a while back emf is produced due to the generation action which is in opposite direction with the supplied voltage. The equation of a dc motor can be written as Vt = Ea + Ia.ra.
Here Vt = terminal voltage.
A general and very basic idea about the working principle of dc motor is given above.
dc shunt motor
For dc motor there is a field connected in parallel or series with the dc motor. Depending on this there are three types of dc motor series motor (where field is connected in series with the motor), shunt motor (where the field is in parallel with the motor) another type of motor is compound motor where series and shunt field both are present in the motor.
Now the main working principle of any dc motor is mainly due to electromagnetic phenomenon, the above mentioned field acts as permanent magnet. The current through the field I flows which marks it a permanent magnet. Now V terminal applied to the motor. We know that where current flows through circuit and that circuit is present inside a magnetic field then there is a torque produced, which is directed towards depending upon the face of the permanent magnets. Same case goes on with dc motors. When V is applied the rotor starts to rotate and then after a while back emf is produced due to the generation action which is in opposite direction with the supplied voltage. The equation of a dc motor can be written as Vt = Ea + Ia.ra.
Here Vt = terminal voltage.
A general and very basic idea about the working principle of dc motor is given above.
What is Thevenin’s theorem ?
In circuit analysis, Thevenin’s theorem for linear electrical network states that any combination of voltage sources, current sources, and resistors with two terminals may be considered as electrically equivalent to a single voltage source V with a single series resistor R. Getting confused ? Let’s make it simpler:
Suppose we have to calculate the current through any branch in a circuit& this branch is connected with of the circuit by its two terminals. As because there are active sources in the circuit so there should be a potential difference between the terminals of the branch & by the potential difference a current is passing through the branch. So, rest of the circuit may be assumed as a single voltage source, whose voltage is the open circuit voltage between the terminals of the said branch & the internal resistance of the circuit is nothing but the equivalent resistance of the circuit looking from into the terminals towards the circuit.
So the Thevenin’s theorem can also be stated as,
• When a particular branch is removed from a circuit, the open circuit voltage appears across the terminals of that circuit, called Thevenin's equivalent voltage.
• The equivalent resistance of the circuit looking from the terminal towards the circuit, is called Thevenin's equivalent resistance.
• Ultimately when we replace the rest of the circuit by a single voltage source, then the voltage of the source would be Thevenin equivalent voltage and internal resistance of the voltage source would be Thevenin's equivalent resistance which would be connected in series.
Thevenin’s theorem is especially useful in analyzing power systems and other circuits where one particular resistor in the circuit (called the “load” resistor) is subject to change, and calculation of the circuit is necessary with each trial value of load resistance, to determine voltage across it and current through it.
Suppose we have to calculate the current through any branch in a circuit& this branch is connected with of the circuit by its two terminals. As because there are active sources in the circuit so there should be a potential difference between the terminals of the branch & by the potential difference a current is passing through the branch. So, rest of the circuit may be assumed as a single voltage source, whose voltage is the open circuit voltage between the terminals of the said branch & the internal resistance of the circuit is nothing but the equivalent resistance of the circuit looking from into the terminals towards the circuit.
So the Thevenin’s theorem can also be stated as,
• When a particular branch is removed from a circuit, the open circuit voltage appears across the terminals of that circuit, called Thevenin's equivalent voltage.
• The equivalent resistance of the circuit looking from the terminal towards the circuit, is called Thevenin's equivalent resistance.
• Ultimately when we replace the rest of the circuit by a single voltage source, then the voltage of the source would be Thevenin equivalent voltage and internal resistance of the voltage source would be Thevenin's equivalent resistance which would be connected in series.
Thevenin’s theorem is especially useful in analyzing power systems and other circuits where one particular resistor in the circuit (called the “load” resistor) is subject to change, and calculation of the circuit is necessary with each trial value of load resistance, to determine voltage across it and current through it.
What is armature resistance?
Armature is the rotating part of dc machine. The resistance offered by the armature circuit is known as armature resistance and is represented by Ra.It usually includes two components . One is the resistance of armature winding and other is the brush contact resistance. The armature resistance depends upon the type of the machine. Except for small machines it is usually of the order of 1Ω.
The voltage drop over the brush contact resistance when current flows from armature segment to brushes and finally to external load is called brush contact drop.It is equal to the product of the values of current and contact resistance. The voltage drop allowed for all brushes of each polarity shall be 1.0 V for carbon or graphite brushes and 3.0 V for metal carbon brushes.
Speed control of dc motor can be obtained by armature and field control methods. One of the methods of armature control is armature resistance control method.
The voltage drop over the brush contact resistance when current flows from armature segment to brushes and finally to external load is called brush contact drop.It is equal to the product of the values of current and contact resistance. The voltage drop allowed for all brushes of each polarity shall be 1.0 V for carbon or graphite brushes and 3.0 V for metal carbon brushes.
Speed control of dc motor can be obtained by armature and field control methods. One of the methods of armature control is armature resistance control method.
What is mesh analysis?
Mesh analysis (or the mesh current method) is a method that is used to solve planar circuits for the currents (and indirectly the voltages) at any place in the circuit. Planar circuits are circuits that can be drawn on a plane surface with no wires crossing each other. A more general technique, called loop analysis (with the corresponding network variables called loop currents) can be applied to any circuit, planar or not. Mesh analysis and loop analysis both make use of Kirchhoff’s voltage law to arrive at a set of equations guaranteed to be solvable if the circuit has a solution. Mesh analysis is usually easier to use when the circuit is planar, compared to loop analysis.Mesh analysis works by arbitrarily assigning mesh currents in the essential meshes (also referred to as independent meshes). An essential mesh is a loop in the circuit that does not contain any other loop.Labels the essential meshes with one, two, and three.
A mesh current is a current that loops around the essential mesh and the equations are set solved in terms of them. A mesh current may not correspond to any physically flowing current, but the physical currents are easily found from them. It is usual practice to have all the mesh currents loop in the same direction. This helps prevent errors when writing out the equations. The convention is to have all the mesh currents looping in a clockwise direction.Shows the same circuit with the mesh currents labeled. Solving for mesh currents instead of directly applying Kirchhoff's current law and Kirchhoff's voltage law can greatly reduce the amount of calculation required. This is because there are fewer mesh currents than there are physical branch currents.
A mesh current is a current that loops around the essential mesh and the equations are set solved in terms of them. A mesh current may not correspond to any physically flowing current, but the physical currents are easily found from them. It is usual practice to have all the mesh currents loop in the same direction. This helps prevent errors when writing out the equations. The convention is to have all the mesh currents looping in a clockwise direction.Shows the same circuit with the mesh currents labeled. Solving for mesh currents instead of directly applying Kirchhoff's current law and Kirchhoff's voltage law can greatly reduce the amount of calculation required. This is because there are fewer mesh currents than there are physical branch currents.
What is series resonant circuit?
An electrical circuit consisting of passive and active elements undergoes resonance when current or voltage in the circuit is maximum or minimum with respect to the magnitude of excitation at a partcular frequency. Also the circuit impedance is minumum or maximum at unity power factor. The phenomenon of resonance is observed in both series or parallel a.c circuits comprising of R, L and C and excited by an a.c source.
Series resonance takes place in an ac circuit which has all the elements connected in series with one another. Let us consider an a.c series circuit with R,L,C.
rcIn this circuit current I is represented as, I = V / Z Amperes
where Z = equivalent impedance of the circuit.
Voltage across the resistance R , inductor L and capacitor C is VR , VL and VC respectively.
We know that impedance Z = R + j ω L + 1 / jω C
= R + j ω L - j / ω C
= R + j ( XL - XC )
where XL = ωL and XC = 1 / ω C
= R + j X , where X = the net reactance
Resonance condition is obtained when XL = XC in series circuit .
Properties of resonance at RLC circuit :
The applied voltage and resulting current are in phase
P.f of series resonant circuit is unity
Net impedance is zero at resonance
Current in the circuit is maximum
At resonance line current in series LCR circuit is maximum hence it is called an acceptor circuit.
At resonance , the circuit has got minimum impedance and maximum admittance
Resonating frequency f0 = 1 / 2 π √ LC.
Series resonance takes place in an ac circuit which has all the elements connected in series with one another. Let us consider an a.c series circuit with R,L,C.
rcIn this circuit current I is represented as, I = V / Z Amperes
where Z = equivalent impedance of the circuit.
Voltage across the resistance R , inductor L and capacitor C is VR , VL and VC respectively.
We know that impedance Z = R + j ω L + 1 / jω C
= R + j ω L - j / ω C
= R + j ( XL - XC )
where XL = ωL and XC = 1 / ω C
= R + j X , where X = the net reactance
Resonance condition is obtained when XL = XC in series circuit .
Properties of resonance at RLC circuit :
The applied voltage and resulting current are in phase
P.f of series resonant circuit is unity
Net impedance is zero at resonance
Current in the circuit is maximum
At resonance line current in series LCR circuit is maximum hence it is called an acceptor circuit.
At resonance , the circuit has got minimum impedance and maximum admittance
Resonating frequency f0 = 1 / 2 π √ LC.
What is Active Filter?
An active filter is a special type of analog electronic filter which involves active electronic elements such as an amplifier, or OpAmp etc. In word active means the power of increasing the signal level, similarly an active filter is able to increase the signal gain along with the filtering. These active components like amplifiers or OpAmp have a unique feature that they are able to boost the signal level. Inclusion of those components in a filter design can be used to improve the performance and increase the versatility of the filter circuit. In frequency domain, the performance of these filters are observed and corrected by changing the overall gain of active elements. Inductors coils are also serve the same, but typically they are expensive compared to other components, so the filtering action is established with low cost electronic elements.
In active filters, the load impedance of the connected circuitry is freed from the voltage current or other characteristics of the filter, which means it is independent from the effect of varying load. Generally active filters are able to produce buffered output, and also able to notching of signals. It is quite cost effective solution for electronic filter circuit, because it serves two purposes, one is filtering the input and other is boosting the energy level. In this way it is able to tasks of two separate elements, they are filter and active source. Butterworth filter is instant of an active filter which is used as the model filter for design purposes.
In active filters, the load impedance of the connected circuitry is freed from the voltage current or other characteristics of the filter, which means it is independent from the effect of varying load. Generally active filters are able to produce buffered output, and also able to notching of signals. It is quite cost effective solution for electronic filter circuit, because it serves two purposes, one is filtering the input and other is boosting the energy level. In this way it is able to tasks of two separate elements, they are filter and active source. Butterworth filter is instant of an active filter which is used as the model filter for design purposes.
What is Steady State Current?
The concept of steady state has relevance in many fields, in particular thermodynamics, economics, and engineering. Steady state is a more general situation than dynamic equilibrium. If a system is in steady state, then the recently observed behavior of the system will continue into the future. In stochastic systems, the probabilities that various states will be repeated will remain constant. In many systems, steady state is not achieved until some time after the system is started or initiated. This initial situation is often identified as a transient state, start-up or warm-up period. While a dynamic equilibrium occurs when two or more reversible processes occur at the same rate, and such a system can be said to be in steady state, a system that is in steady state may not necessarily be in a state of dynamic equilibrium, because some of the processes involved are not reversible. For example: The flow of fluid through a tube or electricity through a network could be in a steady state because there is a constant flow of fluid, or electricity. Conversely, a tank being drained or filled with fluid is a system in transient state, because its volume of fluid changes with time.
What is Voltage Regulator?
Voltage regulator is a device that maintains a constant voltage level. Based on design variable voltage regulator may be provided with negative feedback loop or with feed forward path. Both ac and dc voltage can be regulated using this voltage regulator. Voltage regulators include electronic components and sometimes it uses electro- mechanical mechanism to operate. DC voltage regulator is available in 3 pin IC. So voltage regulators may be electromechanical regulators or electronic regulator. It may be also classified as ac and dc voltage regulator. Electronic voltage regulator is made with resistors and diodes. Both the components are used in series with one another. Electronic voltage regulators are used in computer power supplies, automobile alternators and power station generator plant.
voltage regulatorElectromechanical voltage regulator circuit is provided with a core, spring, solenoid and a capacitor. Here a wire is coiled to make an electromagnet. The magnetic field produced attracts the core by spring action. The current flow produces the field. Regulation quality can be measured by some parameters. Among them two are most important. There are certain other parameters too. Load regulation and line regulation are the most two important parameters. Others are – temperature coefficient, accuracy, dropout voltage, output noise, transient response, etc.
voltage regulatorElectromechanical voltage regulator circuit is provided with a core, spring, solenoid and a capacitor. Here a wire is coiled to make an electromagnet. The magnetic field produced attracts the core by spring action. The current flow produces the field. Regulation quality can be measured by some parameters. Among them two are most important. There are certain other parameters too. Load regulation and line regulation are the most two important parameters. Others are – temperature coefficient, accuracy, dropout voltage, output noise, transient response, etc.
What is Power Factor Correction?
To get the concept of power factor correction, we must know the basic concept of electrical power factor. The electric power is developed in plants, and after that it is distributed among the consumer loads. That is the electrical energy is converted into other forms of energy. In general, power factor is a measure which tells that how efficiently the electric power is utilized to produced other kinds of energy (such as mechanical energy in motor). In fact, it is the ratio of Real or working power to apparent power. Ideally the power factor should be unity. But the consumer loads are mostly inductive in nature, which affects the overall power factor, and also affects the economy of power generation companies. So the power generation companies compensate this inductive power, by means of adding some capacitor element into the network.
They intentionally put some series of capacitor (arrangement is called as capacitor bank) into the circuit. Being capacitive load the capacitor leads the circuit current and compensate the inductive current, drawn by the consumers. In this way, a balanced condition is arises where the power factor becomes more or less unity. Capacitors are actually acts like reactive power generator. Power factor correction units are also necessary for small power applications. Low voltage power factor correction units shapes the input current, which will maximize the real power available from the source. These units are also makes a combination with regulatory elements and used in many low voltage applications such as SMPS. LV power factor correction circuits also use the capacitors. It ensures that the load circuit becomes the linear combination of resistive, inductive and capacitive element, which will maximizes the overall efficiency of the system.
They intentionally put some series of capacitor (arrangement is called as capacitor bank) into the circuit. Being capacitive load the capacitor leads the circuit current and compensate the inductive current, drawn by the consumers. In this way, a balanced condition is arises where the power factor becomes more or less unity. Capacitors are actually acts like reactive power generator. Power factor correction units are also necessary for small power applications. Low voltage power factor correction units shapes the input current, which will maximize the real power available from the source. These units are also makes a combination with regulatory elements and used in many low voltage applications such as SMPS. LV power factor correction circuits also use the capacitors. It ensures that the load circuit becomes the linear combination of resistive, inductive and capacitive element, which will maximizes the overall efficiency of the system.
Advantages of a three phase system
Advantages of a three phase system over a single phase system are:
• The amount of conductor material needed to transfer same amount of power is lesser for three phase system; thus it is more economical.
• Domestic power and industrial power can be distributed from the same source.
• Voltage regulation of a three phase system is quite better.
• As three phase induction motors are self-starting while single phase motors are not, so the three phase system is certainly more advantageous.
• The torque produced by a three phase motor is high.
• For a given size of the frame, three phase generator provides more output.
So,in the field of generation,transmission & distribution,use of three phase system is more economical & versatile.
That's why three phase system is preferred over a single phase system.
• The amount of conductor material needed to transfer same amount of power is lesser for three phase system; thus it is more economical.
• Domestic power and industrial power can be distributed from the same source.
• Voltage regulation of a three phase system is quite better.
• As three phase induction motors are self-starting while single phase motors are not, so the three phase system is certainly more advantageous.
• The torque produced by a three phase motor is high.
• For a given size of the frame, three phase generator provides more output.
So,in the field of generation,transmission & distribution,use of three phase system is more economical & versatile.
That's why three phase system is preferred over a single phase system.
What is lead – acid battery?
Lead–acid batteries are the oldest type of rechargeable battery. The special characteristics of this type of battery is they have a very low energy-to-weight ratio and a low energy-to-volume ratio.Construction: The lead–acid cell can be easily demonstrated using lead plates for the two electrodes. However such a construction produces only around one ampere for postcard sized plates, and for only a few minutes.
Construction:
• The positive plates are the chocolate brown color of lead dioxide.
• The negative are the slate gray of "spongy" lead at the time of manufacture.
• Separators between the positive and negative plates prevent short-circuit through any physical contact.
Applications of lead - acid battery:
• Automotive and traction applications.
• Standby/ Emergency power for electrical installations.
• Submarines.
• UPS.
• Lighting.
• High current drain applications.
Construction:
• The positive plates are the chocolate brown color of lead dioxide.
• The negative are the slate gray of "spongy" lead at the time of manufacture.
• Separators between the positive and negative plates prevent short-circuit through any physical contact.
Applications of lead - acid battery:
• Automotive and traction applications.
• Standby/ Emergency power for electrical installations.
• Submarines.
• UPS.
• Lighting.
• High current drain applications.
What is internal resistance of battery ?
Every electrical equipment has some resistive value. Not only electrical equipment, all the materials in this universe has some non- zero value of resistance. Battery is an electric source so whenever current flows through it, it will offer some resistance to the current and this resistance is referred as internal resistance of battery.
Suppose you are measuring the terminal voltage of a battery, and you are getting E volt. Now you connect one load with that battery and then measure the terminal voltage of that battery. Say, you get voltage V volt. V will obviously be less than E. Actually as soon as the load is connected with the battery, load current IL, starts circulating through the load as well as the battery. During passing through the battery the load current will face some resistance due to which there will be a voltage drop, and due to this terminal voltage V across the battery becomes less than open circuit or no-load voltage E of the battery. If the resistance of battery or the internal resistance of battery is Ri then IL.Ri is the voltage drop due to this battery.
Suppose you are measuring the terminal voltage of a battery, and you are getting E volt. Now you connect one load with that battery and then measure the terminal voltage of that battery. Say, you get voltage V volt. V will obviously be less than E. Actually as soon as the load is connected with the battery, load current IL, starts circulating through the load as well as the battery. During passing through the battery the load current will face some resistance due to which there will be a voltage drop, and due to this terminal voltage V across the battery becomes less than open circuit or no-load voltage E of the battery. If the resistance of battery or the internal resistance of battery is Ri then IL.Ri is the voltage drop due to this battery.
Difference between primary and secondary battery ?
You know about non-chargeable batteries and rechargeable batteries. The non – chargeable batteries are those which can be used once and after its life span it has to be thrown off. Whereas rechargeable batteries can be used repetitively by recharging them with electric energy. The non-chargeable batteries are generally referred as primary batteries where as the rechargeable batteries are referred as secondary batteries. The secondary batteries are also known as storage batteries. Actually in primary battery cells, the chemical reactions responsible for delivering electrical energy, are irreversible. Once the reactions are completed there is no provision of reversing them. On the other hand a secondary cells can be recharged for making them ready for next operation. That means the chemical reactions take place inside the secondary cells are reversible. When load is connected to the secondary batteries, the forward reactions take place in the chemical of the battery for delivering electrical power to the load. This process is known as discharging of battery.
Again when the secondary batteries are connected to the external electrical source, the chemical inside the batteries react in reverse way and the batteries become ready for next discharging operation. This process is known as charging of battery.
Generally, primary cells are low in cast and easy to store and easy to use. Mainly carbon-zinc batteries and Alkaline Batteries predominate the market of primary battery. Although where very tiny current, long service life and very small size are required, Mercury based and Lithium based batteries are used.
Secondary or rechargeable batteries are widely used in industrial and automotive applications. Actually secondary cells are preferred to be used where the user are ready to pay higher initial cost to ensure high current delivery in a consisting and reliable manner. Lead acid and nickel cadmium batteries mainly used for commercial applications. Nickel-hydrogen and silver zinc secondary batteries are used where performance requirements are more important than installation and maintenance cost.
Again when the secondary batteries are connected to the external electrical source, the chemical inside the batteries react in reverse way and the batteries become ready for next discharging operation. This process is known as charging of battery.
Generally, primary cells are low in cast and easy to store and easy to use. Mainly carbon-zinc batteries and Alkaline Batteries predominate the market of primary battery. Although where very tiny current, long service life and very small size are required, Mercury based and Lithium based batteries are used.
Secondary or rechargeable batteries are widely used in industrial and automotive applications. Actually secondary cells are preferred to be used where the user are ready to pay higher initial cost to ensure high current delivery in a consisting and reliable manner. Lead acid and nickel cadmium batteries mainly used for commercial applications. Nickel-hydrogen and silver zinc secondary batteries are used where performance requirements are more important than installation and maintenance cost.
What is constant current source circuit?
Current source circuit is an electronic circuit which deals with electric current. In this circuit current can be absorbed or delivered that is it acts as both source and sink. Current source may be dependent current source as well as independent current source. Independent current source circuit acts as current sink. Electric current is delivered at constant rate. Here the current is independent of the voltage across it.
Constant current source circuits are many. WE can form constant current source circuits in different ways. One of such circuit is formed from JFET that is junction field effect transistor. In this circuit gate is connected to its source. When JFET reaches saturation with constant current value then constant current diode is formed. This happens when drain to source voltage reaches a threshold value. Zener Diode current source is also available.
There are typical constant current source which uses LED instead of zener diode. In this type of circuit there is one limitation, it has imperfect thermal compensation. Constant current source circuit can be made with many analog blocks which include LEDs, op-amps, battery chargers. Also the circuit consists of voltage source, load, resistors and transistors. LED works well when constant current flows through it.
Constant current source circuits are many. WE can form constant current source circuits in different ways. One of such circuit is formed from JFET that is junction field effect transistor. In this circuit gate is connected to its source. When JFET reaches saturation with constant current value then constant current diode is formed. This happens when drain to source voltage reaches a threshold value. Zener Diode current source is also available.
There are typical constant current source which uses LED instead of zener diode. In this type of circuit there is one limitation, it has imperfect thermal compensation. Constant current source circuit can be made with many analog blocks which include LEDs, op-amps, battery chargers. Also the circuit consists of voltage source, load, resistors and transistors. LED works well when constant current flows through it.
What is Constant Voltage Source circuit?
A two terminal device which can maintain fixed voltage is called a voltage source. In case of constant voltage source the output voltage is independent of the load resistance. The output current also does not affect the output voltage of the constant voltage source. Battery, generators acts as very good voltage source. So the constant voltage source can be defined as the voltage source which maintains same voltage level across the terminal (input) irrespective of the current flowing from or into the terminals. In a circuit which has a constant voltage source we get constant voltage value across any resistor which is connected. The current value will vary from resistor to resistor. Let us discuss with an example.
There is a battery voltage source of 10 Volts. If we connect a resistor of 1 ohm or 10 ohm the voltage across them will be the same. Both the voltages will be equal to 10 V. The current will be different if we change the resistance value. Following ohms law V = I/R we get 1 A current for 10 ohm resistor while we get 10 A current for resistor of 1 ohm. Constant or ideal voltage source is also referred to as independent voltage source.
There is a battery voltage source of 10 Volts. If we connect a resistor of 1 ohm or 10 ohm the voltage across them will be the same. Both the voltages will be equal to 10 V. The current will be different if we change the resistance value. Following ohms law V = I/R we get 1 A current for 10 ohm resistor while we get 10 A current for resistor of 1 ohm. Constant or ideal voltage source is also referred to as independent voltage source.
What is absolute permeability ?
In our world, many materials can encourage the development of a magnetic field within it. This term permeability is used in electromagnetism field. If any magnetic or non-magnetic material is subjected to a magnetic field then it will get some amount of magnetization automatically. The amount of magnetization of a material when it is subjected to a magnetic field is called as the permeability of that particular material.
Typically it is a simple ratio of the magnetic flux density to the intensity of the magnetic field in a particular medium. Where, magnetic flux density refers to a vector quantity that measuring the strength and direction of the magnetic field. So, the permeability of a material varies with the medium used, that is if the permeability of a material is " a " when the surrounding medium is air, it is possible that the permeability becomes " b " when the surrounding medium is water. To solve the confusions regarding this issue, permeability is classified in two categories namely absolute permeability and relative permeability. The term absolute permeability refers to the permeability of a material when the surrounding medium is free air.
So, from the definition absolute permeability of a material = B / H .
Where, B is the magnetic flux density & H is the magnetic field. Being a standard value, absolute permeability is also known as the magnetic constant of free space. The standard value of the absolute permeability is equal to 4π × 10-7 Weber per ampere-meter.
Typically it is a simple ratio of the magnetic flux density to the intensity of the magnetic field in a particular medium. Where, magnetic flux density refers to a vector quantity that measuring the strength and direction of the magnetic field. So, the permeability of a material varies with the medium used, that is if the permeability of a material is " a " when the surrounding medium is air, it is possible that the permeability becomes " b " when the surrounding medium is water. To solve the confusions regarding this issue, permeability is classified in two categories namely absolute permeability and relative permeability. The term absolute permeability refers to the permeability of a material when the surrounding medium is free air.
So, from the definition absolute permeability of a material = B / H .
Where, B is the magnetic flux density & H is the magnetic field. Being a standard value, absolute permeability is also known as the magnetic constant of free space. The standard value of the absolute permeability is equal to 4π × 10-7 Weber per ampere-meter.
What is electromagnetic wave?
We know that energy is transferred from one place to another by means of some kind of medium and the medium is pretty essential as it determines the rate of energy transfer. But what happens when there is no medium to transfer energy. How energy can be transferred via vacuum ? The most common example is the sun. Every second huge amount of energy is emitted from the sun which travels in the space and reaches various planets. The energy is transferred by electromagnetic waves. Electromagnetic waves are produced by the electric fields and magnetic fields when they oscillate perpendicular to each other.
The light itself is an electromagnetic wave. So, it can be easily said that the speed of electromagnetic wave is the speed of light i.e., 3 × 108 m/s.
Electromagnetic waves are caused by electromagnetic field. Electromagnetic field is that where both electric field and magnetic field are present. When both of these oscillate perpendicularly to each other, electromagnetic wave is generated which can travel through even vacuum. The energy carried by the electromagnetic wave is called radiant energy. In general, now a days electromagnetic waves transmit radio waves, infra-red radiation, gamma Rays. The wave length of the waves determine the visibility of these electromagnetic waves i.e. depending on the wavelength some waves are visible to bare eyes and some are invisible, it also determines the colour of the wave.
The light itself is an electromagnetic wave. So, it can be easily said that the speed of electromagnetic wave is the speed of light i.e., 3 × 108 m/s.
Electromagnetic waves are caused by electromagnetic field. Electromagnetic field is that where both electric field and magnetic field are present. When both of these oscillate perpendicularly to each other, electromagnetic wave is generated which can travel through even vacuum. The energy carried by the electromagnetic wave is called radiant energy. In general, now a days electromagnetic waves transmit radio waves, infra-red radiation, gamma Rays. The wave length of the waves determine the visibility of these electromagnetic waves i.e. depending on the wavelength some waves are visible to bare eyes and some are invisible, it also determines the colour of the wave.
What is electromagnetic induction ?
Actually, the word 'Induction' comes from the word induced. That means some result coming without direct contact or by induction method. So, electromagnetic induction is the induction of electric current in a coil or circuit due to the magnetic field. So, it can be said that electromagnetic induction is the process where a conductor (coil) is placed in a magnetic field which is changing. Now from Faraday’s law, it can be said that there will be a development of potential in the conductor. Now due to build up of voltage across the conductor a current flows in the circuit which is said to be induced current.
Now coming to the history of electromagnetic induction, Michael Faraday and Joseph Henry first discovered and explained the theory of electromagnetic induction in 1831. In the first practical demonstration of electromagnetic induction Faraday wrapped a ‘torus’ with wires and after sending current through the wires it was seen that there is also current flow in the ring. This practically proved the law of electromagnetic induction.
The quantitative statement of Faraday’s law can be stated as -------
The induced electromagnetic force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux through the circuit.
The main advantage of the electromagnetic induction is that it physically isolates two circuits but electrically connects them. Depending on this principles many costly equipments are provided safety from accidents. Transformer also works on the principle of electromagnetic induction.
Now coming to the history of electromagnetic induction, Michael Faraday and Joseph Henry first discovered and explained the theory of electromagnetic induction in 1831. In the first practical demonstration of electromagnetic induction Faraday wrapped a ‘torus’ with wires and after sending current through the wires it was seen that there is also current flow in the ring. This practically proved the law of electromagnetic induction.
The quantitative statement of Faraday’s law can be stated as -------
The induced electromagnetic force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux through the circuit.
The main advantage of the electromagnetic induction is that it physically isolates two circuits but electrically connects them. Depending on this principles many costly equipments are provided safety from accidents. Transformer also works on the principle of electromagnetic induction.
What is electric flux?
If we say that the cause is electric field then we can say that electric flux is the result of that. So electric flux is nothing but the flow of electrical field through an unit area. If we assume the electrical field to be perpendicular with the area it is flowing through , then there is no complexity in determining the electrical flux φ and S is the area of the surface,
φ = E.S = E.S.cosθ
For perpendicular θ = 90o and θ is the angle if the flow of electrical field is not perpendicular with the area and that angle.
The unit of electric flux is tesla which is actually Weber/m2, where Weber is the unit of electrical field which is actually nothing but V/m.
Now depending on the type of electric field the flux can be of two types. If the field is uniform then the flux will be uniform as well, i.e. the flow of field line will be equally distributed through the area, on the other hand if the field is non uniform, then the field lines are not equally distributed throughout the area, so the flux of this area will be non uniform too. The flux determines the strength of an electric field.
φ = E.S = E.S.cosθ
For perpendicular θ = 90o and θ is the angle if the flow of electrical field is not perpendicular with the area and that angle.
The unit of electric flux is tesla which is actually Weber/m2, where Weber is the unit of electrical field which is actually nothing but V/m.
Now depending on the type of electric field the flux can be of two types. If the field is uniform then the flux will be uniform as well, i.e. the flow of field line will be equally distributed through the area, on the other hand if the field is non uniform, then the field lines are not equally distributed throughout the area, so the flux of this area will be non uniform too. The flux determines the strength of an electric field.
What is the difference between emf and potential difference?
As per the definition the emf or the electromotive force describes the force required to separate two charges at a given distance. Originally, emf was supposed to relate to problems involving moving charges, but early on, emf got adopted as being synonymous with "battery" or "voltage source".
Potential difference is simply a voltage difference between two points in a closed electrical circuit with a voltage source circuit (or in free space). So, the interesting fact is the potential difference can be a source of emf if it is used to move charges. The term ‘potential difference’ is a general term and found in all the energy fields such as electric, magnetic and gravitational fields. But emf is only pertaining to electrical circuits. Although, both ‘electrical potential difference’ and emf are measured in Volts (V), there are many differences between them.
Potential Difference
Potential is a function of the location, and potential difference between point A and point B is calculated by subtracting the potential of A from potential of B. In an electric field, it is the amount work to be done to move a unit charge (+1 Coulomb) from B to A. Electric potential difference is measured in V (Volts). In an electrical circuit, current flows from the higher potential to lower potential.
EMF (Electromotive Force)
EMF is the electrical potential difference provided by an energy source like battery. Varying magnetic fields also can generate an EMF according to the Faraday’s law. Although EMF is also a voltage and measured in Volts (V), it is all about the generation of a potential difference.
So the important differences between Voltage and EMF is:
The term ‘potential difference’ is used in all energy fields (electric, magnetic, gravitational), and ‘EMF’ is only used in electric circuits.
EMF is the electrical potential difference generated by a source like battery or generator.
We can measure potential difference between any two points, but EMF exists only between the two ends of a source.
Sum of ‘potential drops’ around a circuit is equal to total EMF according to Kirchhoff’s second law.
Potential difference is simply a voltage difference between two points in a closed electrical circuit with a voltage source circuit (or in free space). So, the interesting fact is the potential difference can be a source of emf if it is used to move charges. The term ‘potential difference’ is a general term and found in all the energy fields such as electric, magnetic and gravitational fields. But emf is only pertaining to electrical circuits. Although, both ‘electrical potential difference’ and emf are measured in Volts (V), there are many differences between them.
Potential Difference
Potential is a function of the location, and potential difference between point A and point B is calculated by subtracting the potential of A from potential of B. In an electric field, it is the amount work to be done to move a unit charge (+1 Coulomb) from B to A. Electric potential difference is measured in V (Volts). In an electrical circuit, current flows from the higher potential to lower potential.
EMF (Electromotive Force)
EMF is the electrical potential difference provided by an energy source like battery. Varying magnetic fields also can generate an EMF according to the Faraday’s law. Although EMF is also a voltage and measured in Volts (V), it is all about the generation of a potential difference.
So the important differences between Voltage and EMF is:
The term ‘potential difference’ is used in all energy fields (electric, magnetic, gravitational), and ‘EMF’ is only used in electric circuits.
EMF is the electrical potential difference generated by a source like battery or generator.
We can measure potential difference between any two points, but EMF exists only between the two ends of a source.
Sum of ‘potential drops’ around a circuit is equal to total EMF according to Kirchhoff’s second law.
What is the direction of conventional current flow?
In a closed circuit with a voltage source, there should be a flow of positive charges (+) & a flow of negative charges (−) but in opposite direction to each other. The flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction.
Now the interesting fact arises, since current can be the flow of either positive or negative charges, what should be the actual direction of the conventional current flow? The solution of the mystery is the direction of conventional current is defined arbitrarily to be the direction of the flow of positive charges. As the negative charges or electrons flows from the negative terminal (−)to positive terminal(+) of the voltage source, so we can say that conventional current flows on the opposite direction, that is positive terminal(+) to the negative terminal(−) of the same voltage source.
In electrical circuits, most widely used conductors are made of metals like copper & aluminium. But in metals, positive charges are immobile, and the charge carriers are electrons, but we know that electrons carries the negative charges.
So by the above discussion ,we can say that electron motion in a conductor is in the direction opposite to that of conventional (or electric) current. It is a easy & daily application of the conventional current flow theory.
Now the interesting fact arises, since current can be the flow of either positive or negative charges, what should be the actual direction of the conventional current flow? The solution of the mystery is the direction of conventional current is defined arbitrarily to be the direction of the flow of positive charges. As the negative charges or electrons flows from the negative terminal (−)to positive terminal(+) of the voltage source, so we can say that conventional current flows on the opposite direction, that is positive terminal(+) to the negative terminal(−) of the same voltage source.
In electrical circuits, most widely used conductors are made of metals like copper & aluminium. But in metals, positive charges are immobile, and the charge carriers are electrons, but we know that electrons carries the negative charges.
So by the above discussion ,we can say that electron motion in a conductor is in the direction opposite to that of conventional (or electric) current. It is a easy & daily application of the conventional current flow theory.
What is drift current?
Drift current is the electric current, or movement of charge carriers, which is due to an electric field applied to a circuit, or may be considered as due to a electromotive force over a certain distance. When an electric field that is a potential difference applied across a semiconductor material, the drift current is produced due to flow of charge carriers. The drift velocity is the average velocity of the charge carriers present in the drift current.
If an electric field is applied to an electron (−) existing in a free space, it will accelerate the electron in a straight line from the negative(−) terminal to the positive terminal(+) of the applied voltage source. But the same thing does not happen in the case of electrons available in good conductors ,that is in metals like copper, aluminium etc. Because good conductors have huge numbers of free electrons moving randomly & this random movement of electrons will drift according to the direction of applied electric field and random movement of electrons in a straight line is known as drift current. Drift current also depends on the mobility of charge carriers in the respective conducting medium.
Drift current in a p-n junction diode:
In a p-n junction diode, electrons are the minority charge carriers in the p-region and holes(positive charges) are the minority charge carriers in the n-region. Due to the diffusion of charge carriers, the diffusion current, which flows from the p to n region, is exactly balanced by the equal and opposite drift current. But as minority charge carriers can be thermally generated, drift current is temperature dependent. When an electric field is applied across the semiconductor material, the charge carriers attain a certain drift velocity . This combined effect of movement of the charge carriers constitutes a current known as "drift current". Drift current due to the charge carriers such as free electrons and holes is the current passing through a square centimetre area perpendicular to the direction of flow.
Drift current density, due to free electrons is given by:
Jn = qnE Amp / cm2
Drift current density, due to holes is given by:
Jp = qpE Amp / cm2
n - Number of free electrons per cubic centimetre.
p - Number of holes per cubic centimetre.
E – Applied Electric Field Intensity in V /cm.
q – Charge of an electron = 1.6 × 10−19 coulomb.
If an electric field is applied to an electron (−) existing in a free space, it will accelerate the electron in a straight line from the negative(−) terminal to the positive terminal(+) of the applied voltage source. But the same thing does not happen in the case of electrons available in good conductors ,that is in metals like copper, aluminium etc. Because good conductors have huge numbers of free electrons moving randomly & this random movement of electrons will drift according to the direction of applied electric field and random movement of electrons in a straight line is known as drift current. Drift current also depends on the mobility of charge carriers in the respective conducting medium.
Drift current in a p-n junction diode:
In a p-n junction diode, electrons are the minority charge carriers in the p-region and holes(positive charges) are the minority charge carriers in the n-region. Due to the diffusion of charge carriers, the diffusion current, which flows from the p to n region, is exactly balanced by the equal and opposite drift current. But as minority charge carriers can be thermally generated, drift current is temperature dependent. When an electric field is applied across the semiconductor material, the charge carriers attain a certain drift velocity . This combined effect of movement of the charge carriers constitutes a current known as "drift current". Drift current due to the charge carriers such as free electrons and holes is the current passing through a square centimetre area perpendicular to the direction of flow.
Drift current density, due to free electrons is given by:
Jn = qnE Amp / cm2
Drift current density, due to holes is given by:
Jp = qpE Amp / cm2
n - Number of free electrons per cubic centimetre.
p - Number of holes per cubic centimetre.
E – Applied Electric Field Intensity in V /cm.
q – Charge of an electron = 1.6 × 10−19 coulomb.
Over Current Relay Working Principle and Types
In an over current relay or o/c relay the actuating quantity is only current. There is only one current operated element in the relay, no voltage coil etc. are required to construct this protective relay.
Working Principle of Over Current Relay
In an over current relay, there would be essentially a current coil. When normal electric current flows through this coil, the magnetic effect generated by the coil is not sufficient to move the moving element of the relay, as in this condition the restraining force is greater than deflecting force. But when the current through the coil increased, the magnetic effect increases, and after certain level of current, the deflecting force generated by the magnetic effect of the coil, crosses the restraining force, as a result, the moving element starts moving to change the contact position in the relay.
Although there are different types of over current relays but basic working principle of over current relay is more or less same for all.
Types of Over Current Relay
Depending upon time of operation, there are various types of OC relays, such as,
Inverse time over current relay or simply inverse OC relay is again subdivided as inverse definite minimum time (IDMT), very inverse time, extremely inverse time over current relay or OC relay.
Working Principle of Over Current Relay
In an over current relay, there would be essentially a current coil. When normal electric current flows through this coil, the magnetic effect generated by the coil is not sufficient to move the moving element of the relay, as in this condition the restraining force is greater than deflecting force. But when the current through the coil increased, the magnetic effect increases, and after certain level of current, the deflecting force generated by the magnetic effect of the coil, crosses the restraining force, as a result, the moving element starts moving to change the contact position in the relay.
Although there are different types of over current relays but basic working principle of over current relay is more or less same for all.
Types of Over Current Relay
Depending upon time of operation, there are various types of OC relays, such as,
- Instantaneous over current relay.
- Definite time over current relay.
- Inverse time over current relay.
Inverse time over current relay or simply inverse OC relay is again subdivided as inverse definite minimum time (IDMT), very inverse time, extremely inverse time over current relay or OC relay.
Protective Relay
A relay is automatic device which senses an abnormal condition of electrical circuit and closes its contacts. These contacts in turns close and complete the circuit breaker trip coil circuit hence make the circuit breaker tripped for disconnecting the faulty portion of the electrical circuit from rest of the healthy circuit.
Pickup level of actuating signal: The value of actuating quantity (voltage or current) which is on threshold above which the relay initiates to be operated.
If the value of actuating quantity is increased, the electromagnetic effect of the relay coil is increased and above a certain level of actuating quantity the moving mechanism of the relay just starts to move.
Reset level: The value of electric current or voltage below which a relay opens its contacts and comes in original position.
Operating time of relay -Just after exceeding pickup level of actuating quantity the moving mechanism (for example rotating disc) of relay starts moving and it ultimately close the relay contacts at the end of its journey. The time which elapses between the instant when actuating quantity exceeds the pickup value to the instant when the relay contacts close.
Reset time of relay – The time which elapses between the instant when the actuating quantity becomes less than the reset value to the instant when the relay contacts returns to its normal position.
Reach of relay – A distance relay operates whenever the distance seen by the relay is less than the pre-specified impedance. The actuating impedance in the relay is the function of distance in a distance protection relay. This impedance or corresponding distance is called reach of the relay.
Pickup level of actuating signal: The value of actuating quantity (voltage or current) which is on threshold above which the relay initiates to be operated.
If the value of actuating quantity is increased, the electromagnetic effect of the relay coil is increased and above a certain level of actuating quantity the moving mechanism of the relay just starts to move.
Reset level: The value of electric current or voltage below which a relay opens its contacts and comes in original position.
Operating time of relay -Just after exceeding pickup level of actuating quantity the moving mechanism (for example rotating disc) of relay starts moving and it ultimately close the relay contacts at the end of its journey. The time which elapses between the instant when actuating quantity exceeds the pickup value to the instant when the relay contacts close.
Reset time of relay – The time which elapses between the instant when the actuating quantity becomes less than the reset value to the instant when the relay contacts returns to its normal position.
Reach of relay – A distance relay operates whenever the distance seen by the relay is less than the pre-specified impedance. The actuating impedance in the relay is the function of distance in a distance protection relay. This impedance or corresponding distance is called reach of the relay.
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