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.
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