INTRODUCTION OF THE TRANSFORMER
CONTENT
1) DEFINITION OF A TRANSFORMER
2)WORKING PRINCIPLE
3) PRINCIPLE OF TRANSFORMER OPERATION IN DETAIL
4) PARTS OF A TRANSFORMER
5) TYPES OF TRANSFORMER
6) CONSTRUCTION
7) LOSSES OF TRANSFORMER
8) EMF EQUATION OF THE TRANSFORMER
9) TURNS RATIO OF THE COIL OF THE TRANSFORMER
10) OPEN CIRCUIT & SHORT CIRCUIT TEST
11) EFFICIENCY
12) APPLICATION
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| A TRANSFORMER |
Definition of a transformer:- A transformer is a static electrical device that transfers electrical energy from one electrical circuit to another (one or more) circuit.
An alternating current in any one coil of the transformer produces a varying magnetic flux which in turn produces or induces a varying electromotive force across any other coils wound around the same core. Electrical energy can be transferred between the (possibly many) coils, without a metallic connection between the two circuits.
WORKING PRINCIPLE OF A TRANSFORMER
Our transformer works on the principal of “FARADAY’S LAWS OF INDUCTION” which was discovered in 1831. It also described the induced voltage effect in any coil due to changing magnetic flux encircled by the coil. This is used for increasing alternating voltage at low current or decreasing the alternating voltage at high current in electrical power application and for coupling the stages of signal processing circuits
FARADAY'S LAWS OF INDUCTION :-
FIRST LAW :- Any change in the magnetic field of a coil of wire will cause an emf to be induced in the coil. This emf induced is called induced emf (ELECTRO MOTIVE FORCE) and if the conductor circuit is closed , then the current will also circulate through the circuit and this current is called induced emf.
SECOND LAW :- It states that the magnitude of emf induced in the coil is equal to the rate of change of flux that linkages with the coil. The flux linkages of the coil is the product of the number of turns in the coil and flux associated with the coil.
FARADAY'S LAWS OF INDUCTION :-
FIRST LAW :- Any change in the magnetic field of a coil of wire will cause an emf to be induced in the coil. This emf induced is called induced emf (ELECTRO MOTIVE FORCE) and if the conductor circuit is closed , then the current will also circulate through the circuit and this current is called induced emf.
SECOND LAW :- It states that the magnitude of emf induced in the coil is equal to the rate of change of flux that linkages with the coil. The flux linkages of the coil is the product of the number of turns in the coil and flux associated with the coil.
A small history of a transformer
The invention of the first constant-potential transformer in 1885, transformers have become essential for the transmission, distribution, and utilization of alternating current electric power.
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PRINCIPLE OPERATION OF TRANSFORMER
The main principle of operation of a transformer is mutual inductance between two circuits which is linked by a common magnetic flux. A basic transformer consists of two coils that are electrically separate and inductive, but are magnetically linked through a path of reluctance.
The core laminations are joined in the form of strips in between the strips you can see that there are some narrow gaps right through the cross-section of the core.
Both the coils have high mutual inductance. A mutual electro-motive force is induced in the transformer from the alternating flux that is set up in the laminated core, due to the coil that is connected to a source of alternating voltage. Most of the alternating flux developed by this coil is linked with the other coil and thus produces the mutual induced electro-motive force. The so produced electro-motive force can be explained with the help of Faraday’s laws of Electromagnetic Induction as (e=M*dI/dt). If the second coil circuit is closed, a current flows in it and thus electrical energy is transferred magnetically from the first to the second coil. The alternating current supply is given to the first coil and hence it can be called as the primary winding. The energy is drawn out from the second coil and thus can be called as the secondary winding.
In short, a transformer carries the operations:
1)Transfer of electric power from one circuit to another.
2)Transfer of electric power without any change in frequency.
3)Transfer with the principle of electromagnetic induction.
4)The two electrical circuits are linked by mutual induction.
Basic Parts of a Transformer
These are the basic components of a transformer.
1) Laminated core
2) Windings
3) Insulating materials
4) Transformer oil
5) Tap changer
6) Oil Conservator
7) Breather
8) Cooling tubes
9) Buchholz Relay
10) Explosion vent
Of the above, laminated soft iron core, windings and insulating material are the primary parts and are present in all transformers, whereas the rest can be seen only in transformers having a capacity of more than 100KVA.
Now let us discuss about them
1) Laminated core -
The core acts as support to the winding in the transformer. It also provides a low reluctance path to the flow of magnetic flux. It is made of laminated soft iron (material used as silicon steel) core in order to reduce eddy current loss and Hysteresis loss. The composition of a transformer core depends on such as factors voltage, current, and frequency. The diameter of the transformer core is directly proportional to copper loss and is inversely proportional to iron loss. If the diameter of the core is decreased, the weight of the steel in the core is reduced, which leads to less core loss of the transformer and the copper loss increase. When the diameter of the core is increased, the vise versa occurs.
OPEN CIRCUIT & SHORT CIRCUIT TEST
EFFICIENCY OF THE TRANSFORMER
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PRINCIPLE OPERATION OF TRANSFORMER
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The main principle of operation of a transformer is mutual inductance between two circuits which is linked by a common magnetic flux. A basic transformer consists of two coils that are electrically separate and inductive, but are magnetically linked through a path of reluctance.
The core laminations are joined in the form of strips in between the strips you can see that there are some narrow gaps right through the cross-section of the core.
Both the coils have high mutual inductance. A mutual electro-motive force is induced in the transformer from the alternating flux that is set up in the laminated core, due to the coil that is connected to a source of alternating voltage. Most of the alternating flux developed by this coil is linked with the other coil and thus produces the mutual induced electro-motive force. The so produced electro-motive force can be explained with the help of Faraday’s laws of Electromagnetic Induction as (e=M*dI/dt). If the second coil circuit is closed, a current flows in it and thus electrical energy is transferred magnetically from the first to the second coil. The alternating current supply is given to the first coil and hence it can be called as the primary winding. The energy is drawn out from the second coil and thus can be called as the secondary winding.
In short, a transformer carries the operations:
1)Transfer of electric power from one circuit to another.
2)Transfer of electric power without any change in frequency.
3)Transfer with the principle of electromagnetic induction.
4)The two electrical circuits are linked by mutual induction.
THE PARTS OF A TRANSFORMER
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| SOME PARTS ARE MENTIONED |
Basic Parts of a Transformer
These are the basic components of a transformer.
1) Laminated core
2) Windings
3) Insulating materials
4) Transformer oil
5) Tap changer
6) Oil Conservator
7) Breather
8) Cooling tubes
9) Buchholz Relay
10) Explosion vent
Of the above, laminated soft iron core, windings and insulating material are the primary parts and are present in all transformers, whereas the rest can be seen only in transformers having a capacity of more than 100KVA.
Now let us discuss about them
1) Laminated core -
The core acts as support to the winding in the transformer. It also provides a low reluctance path to the flow of magnetic flux. It is made of laminated soft iron (material used as silicon steel) core in order to reduce eddy current loss and Hysteresis loss. The composition of a transformer core depends on such as factors voltage, current, and frequency. The diameter of the transformer core is directly proportional to copper loss and is inversely proportional to iron loss. If the diameter of the core is decreased, the weight of the steel in the core is reduced, which leads to less core loss of the transformer and the copper loss increase. When the diameter of the core is increased, the vise versa occurs.
2) WINDINGS :-
Two sets of winding are made over the transformer core and are insulated from each other. Winding consists of several turns of copper conductors bundled together, and connected connected in series. Now we should know why we use copper. 1)Copper has high conductivity. 2)This minimizes losses as well as the amount of copper needed for the winding (volume & weight of winding).
3)Copper has high ductility. This means it can be easily bend conductors into tight windings around the transformer's core, thus minimizing the amount of copper needed as well as the overall volume of the winding.
The transformer windings are classified into many ways such as a) based on voltage range and 2)based on input and output voltage.
BASED ON INPUT AND OUTPUT
1) PRIMARY WINDING - These are the winding to which the input voltage is applied.
2) SECONDARY WINDING - These are the winding to which the output voltage is taken.
BASED ON VOLTAGE RANGE
1) HIGH VOLTAGE - It is made of copper conductor. The number of turns made shall be the multiple of the number of turns in the low voltage winding. The conductor used will be thinner than that of the low voltage winding.
2) LOW VOLTAGE - It is made of thick copper conductors. This is because the current in the low voltage winding is higher than that of high voltage winding.
Input supply to the transformers can be applied from either low voltage (LV) or high voltage (HV) winding based on the requirement.
3) INSULATING MATERIALS
Insulating paper and cardboard are used in transformers to isolate primary and secondary winding from each other and from the transformer core.
4) TRANSFORMER OIL
Transformer oil is another insulating material. Transformer oil performs two important functions: in addition to insulating function, it can also cool the core and coil assembly. The transformer's core and winding must be completely immersed in the oil. Normally, hydrocarbon mineral oils are used as transformer oil.
5) TAP CHANGER
The output voltage of transformers vary according to its input voltage and the load. During loaded conditions, the voltage on the output terminal decreases, whereas during off-load conditions the output voltage increases. In order to balance the voltage variations, tap changers are used. Tap changers can be either on-load tap changers or off-load tap changers. In an on-load tap changer, the tapping can be changed without isolating the transformer from the supply. In an off-load tap changer, it is done after disconnecting the transformer. Automatic tap changers are also available.
6) OIL CONSERVATOR TANK
The conservator conserves the transformer oil. It is an airtight, metallic, cylindrical drum that is fitted above the transformer. The conservator tank is vented to the atmosphere at the top, and the normal oil level is approximately in the middle of the conservator to allow the oil to expand and contract as the temperature varies. The conservator is connected to the main tank inside the transformer, which is completely filled with transformer oil through a pipeline.
7) BREATHER
The breather controls the moisture level in the transformer. Moisture can arise when temperature variations cause expansion and contraction of the insulating oil, which then causes the pressure to change inside the conservator. Pressure changes are balanced by a flow of atmospheric air in and out of the conservator, which is how moisture can enter the system.
If the insulating oil encounters moisture, it can affect the paper insulation or may even lead to internal faults. Therefore, it is necessary that the air entering the tank is moisture-free.
The transformer's breather is a cylindrical container that is filled with silica gel. When the atmospheric air passes through the silica gel of the breather, the air's moisture is absorbed by the silica crystals. The breather acts like an air filter for the transformer and controls the moisture level inside a transformer. It is connected to the end of breather pipe.
8) COOLING TUBE
Cooling tubes are used to cool the transformer oil. The transformer oil is circulated through the cooling tubes. The circulation of the oil may either be natural or forced. In natural circulation, when the temperature of the oil rises the hot oil naturally rises to the top and the cold oil sinks downward. Thus the oil naturally circulates through the tubes. In forced circulation, an external pump is used to circulate the oil.
9) BUCHHOLZ RELAY
The Buchholz Relay is a protective device container housed over the connecting pipe from the main tank to the conservator tank. It is used to sense the faults occurring inside the transformer. It is a simple relay that is operated by the gases emitted during the decomposition of transformer oil during internal faults. It helps in sensing and protecting the transformer from internal faults.
10) EXPLOSION VENT
The explosion vent is used to expel boiling oil in the transformer during heavy internal faults in order to avoid the explosion of the transformer. During heavy faults, the oil rushes out of the vent. The level of the explosion vent is normally maintained above the level of the conservatory tank.
The output voltage of transformers vary according to its input voltage and the load. During loaded conditions, the voltage on the output terminal decreases, whereas during off-load conditions the output voltage increases. In order to balance the voltage variations, tap changers are used. Tap changers can be either on-load tap changers or off-load tap changers. In an on-load tap changer, the tapping can be changed without isolating the transformer from the supply. In an off-load tap changer, it is done after disconnecting the transformer. Automatic tap changers are also available.
INTERNAL SYSTEM OF TAP CHANGER
ON LOAD TAP CHANGER (OLTC)
OFF LOAD TAP CHANGER
6) OIL CONSERVATOR TANK
The conservator conserves the transformer oil. It is an airtight, metallic, cylindrical drum that is fitted above the transformer. The conservator tank is vented to the atmosphere at the top, and the normal oil level is approximately in the middle of the conservator to allow the oil to expand and contract as the temperature varies. The conservator is connected to the main tank inside the transformer, which is completely filled with transformer oil through a pipeline.
7) BREATHER
The breather controls the moisture level in the transformer. Moisture can arise when temperature variations cause expansion and contraction of the insulating oil, which then causes the pressure to change inside the conservator. Pressure changes are balanced by a flow of atmospheric air in and out of the conservator, which is how moisture can enter the system.
If the insulating oil encounters moisture, it can affect the paper insulation or may even lead to internal faults. Therefore, it is necessary that the air entering the tank is moisture-free.
The transformer's breather is a cylindrical container that is filled with silica gel. When the atmospheric air passes through the silica gel of the breather, the air's moisture is absorbed by the silica crystals. The breather acts like an air filter for the transformer and controls the moisture level inside a transformer. It is connected to the end of breather pipe.
8) COOLING TUBE
Cooling tubes are used to cool the transformer oil. The transformer oil is circulated through the cooling tubes. The circulation of the oil may either be natural or forced. In natural circulation, when the temperature of the oil rises the hot oil naturally rises to the top and the cold oil sinks downward. Thus the oil naturally circulates through the tubes. In forced circulation, an external pump is used to circulate the oil.
9) BUCHHOLZ RELAY
The Buchholz Relay is a protective device container housed over the connecting pipe from the main tank to the conservator tank. It is used to sense the faults occurring inside the transformer. It is a simple relay that is operated by the gases emitted during the decomposition of transformer oil during internal faults. It helps in sensing and protecting the transformer from internal faults.
10) EXPLOSION VENT
The explosion vent is used to expel boiling oil in the transformer during heavy internal faults in order to avoid the explosion of the transformer. During heavy faults, the oil rushes out of the vent. The level of the explosion vent is normally maintained above the level of the conservatory tank.
TYPES OF TRANSFORMER
INSTRUMENTAL TRANSFORMER :-Instrument transformers are high accuracy class electrical devices used to isolate or transform voltage or current levels. The most common usage of instrument transformers is to operate instruments or metering from high voltage or high current circuits, safely isolating secondary control circuitry from the high voltages or currents. The primary winding of the transformer is connected to the high voltage or high current circuit, and the meter or relay is connected to the secondary circuit. Instrument transformers may also be used as an isolation transformer so that secondary quantities may be used in phase shifting without affecting other primary connected devices.
Examples :- current transformer (C.T)
potential transformers (P.T)
SINGLE PHASE AND THREE PHASE TRANSFORMER:-
A single-phase transformer is a type of power transformer that utilizes single-phase alternating current, meaning the transformer relies on a voltage cycle that operates in a unified time phase.
A three phase transformer is a three-legged iron core. Each leg has a respective primary and secondary winding. Most power is dispersed in the form of three-phase AC.
POWER TRANSFORMER :-Power transformers are generally used in transmission network for stepping up or down the voltage level. It operates through out the day and has maximum efficiency at percentage of full load where no load loss equal load loss. It is generally rated at higher MVA and it is used in step up and step down application in transmission. They are bigger in size.
DISTRIBUTION TRANSFORMER :- A distribution transformer or service transformer is a transformer that provides the final voltage transformation in the electric power distribution system, stepping down the voltage used in the distribution lines to the level used by the customer.
STEP UP AND STEP DOWN TRANSFORMERS
STEP UP TRANSFORMERS - A transformer in which the output (secondary) voltage is greater than its input (primary) voltage is called a step-up transformer. The step-up transformer decreases the output current for keeping the input and output power of the system equal.
The number of turns on the secondary of the transformer is greater than that of the primary.
APPLICATION - used in transmission lines
STEP DOWN TRANSFORMERS -
A transformer in which the output (secondary) voltage is less than its input (primary) voltage is called a step-down transformer. The number of turns on the primary of the transformer is greater than the turn on the secondary of the TRANSFORMER.
APPLICATION - used in door bells and home appliances.
CONSTRUCTION
Transformer Construction of the Core:- Generally, the name associated with the construction of a transformer is dependent upon how the primary and secondary windings are wound around the central laminated steel core. The two most common and basic designs of transformer construction are the Closed-core Transformer and the Shell-core Transformer.
In the “closed-core” type (core form) transformer, the primary and secondary windings are wound outside and surround the core ring. In the “shell type” (shell form) transformer, the primary and secondary windings pass inside the steel magnetic circuit (core) which forms a shell around the windings.
In both types of transformer core design, the magnetic flux linking the primary and secondary windings travels entirely within the core with no loss of magnetic flux through air. In the core type transformer construction, one half of each winding is wrapped around each leg (or limb) of the transformers magnetic circuit.
The coils are not arranged with the primary winding on one leg and the secondary on the other but instead half of the primary winding and half of the secondary winding are placed one over the other concentrically on each leg in order to increase magnetic coupling allowing practically all of the magnetic lines of force go through both the primary and secondary windings at the same time. However, with this type of transformer construction, a small percentage of the magnetic lines of force flow outside of the core, and this is called “leakage flux”.
Shell type transformer cores overcome this leakage flux as both the primary and secondary windings are wound on the same centre leg or limb which has twice the cross-sectional area of the two outer limbs. The advantage here is that the magnetic flux has two closed magnetic paths to flow around external to the coils on both left and right hand sides before returning back to the central coils.This means that the magnetic flux circulating around the outer limbs of this type of transformer construction is equal to Φ/2. As the magnetic flux has a closed path around the coils, this has the advantage of decreasing core losses and increasing overall efficiency.
Most of the times in industries shell type core transformers are made. This are made because the winding gets protection against the mechanical damage. It also gets better support for electromagnetic forces between current carrying conductors.
LOSSES OF TRANSFORMER
The main losses of a transformer are heat loss or copper loss (I 2R), Eddy current loss, Hysteresis loss.
Hysteresis Losses:-Transformer Hysteresis Losses are caused because of the friction of the molecules against the flow of the magnetic lines of force required to magnetize the core, which are constantly changing in value and direction first in one direction and then the other due to the influence of the sinusoidal supply voltage. This molecular friction causes heat to be developed which represents an energy loss to the transformer. Excessive heat loss can overtime shorten the life of the insulating materials used in the manufacture of the windings and structures. Therefore, cooling of a transformer is important. Also, transformers are designed to operate at a particular supply frequency. Lowering the frequency of the supply will result in increased hysteresis and higher temperature in the iron core. So reducing the supply frequency from 60 Hertz to 50 Hertz will raise the amount of hysteresis present, decreased the VA capacity of the transformer.
Eddy Current Losses or iron loss :- Transformer Eddy Current Losses on the other hand are caused by the flow of circulating currents induced into the steel caused by the flow of the magnetic flux around the core. These circulating currents are generated because to the magnetic flux the core is acting like a single loop of wire. Since the iron core is a good conductor, the eddy currents induced by a solid iron core will be large. Eddy currents do not contribute anything towards the usefulness of the transformer but instead they oppose the flow of the induced current by acting like a negative force generating resistive heating and power loss within the core.
Copper Losses:- But there is also another type of energy loss associated with transformers called “copper losses”. Transformer Copper Losses are mainly due to the electrical resistance of the primary and secondary windings. Most transformer coils are made from copper wire which has resistance in Ohms. This resistance opposes the magnetizing currents flowing through them. When a load is connected to the transformers secondary winding, large electrical currents flow in both the primary and the secondary windings, electrical energy and power (or the I2 R) losses occur as heat. Generally copper losses vary with the load current, being almost zero at no-load, and at a maximum at full-load when current flow is at maximum.
EMF EQUATION OF THE TRANSFORMER
The transformer works based on the FARADAY'S LAWS OF ELECTROMAGNETIC INDUCTION.
CONSTRUCTION
Transformer Construction of the Core:- Generally, the name associated with the construction of a transformer is dependent upon how the primary and secondary windings are wound around the central laminated steel core. The two most common and basic designs of transformer construction are the Closed-core Transformer and the Shell-core Transformer.
In the “closed-core” type (core form) transformer, the primary and secondary windings are wound outside and surround the core ring. In the “shell type” (shell form) transformer, the primary and secondary windings pass inside the steel magnetic circuit (core) which forms a shell around the windings.
In both types of transformer core design, the magnetic flux linking the primary and secondary windings travels entirely within the core with no loss of magnetic flux through air. In the core type transformer construction, one half of each winding is wrapped around each leg (or limb) of the transformers magnetic circuit.
The coils are not arranged with the primary winding on one leg and the secondary on the other but instead half of the primary winding and half of the secondary winding are placed one over the other concentrically on each leg in order to increase magnetic coupling allowing practically all of the magnetic lines of force go through both the primary and secondary windings at the same time. However, with this type of transformer construction, a small percentage of the magnetic lines of force flow outside of the core, and this is called “leakage flux”.
Shell type transformer cores overcome this leakage flux as both the primary and secondary windings are wound on the same centre leg or limb which has twice the cross-sectional area of the two outer limbs. The advantage here is that the magnetic flux has two closed magnetic paths to flow around external to the coils on both left and right hand sides before returning back to the central coils.This means that the magnetic flux circulating around the outer limbs of this type of transformer construction is equal to Φ/2. As the magnetic flux has a closed path around the coils, this has the advantage of decreasing core losses and increasing overall efficiency.
Most of the times in industries shell type core transformers are made. This are made because the winding gets protection against the mechanical damage. It also gets better support for electromagnetic forces between current carrying conductors.
LOSSES OF TRANSFORMER
The main losses of a transformer are heat loss or copper loss (I 2R), Eddy current loss, Hysteresis loss.
Hysteresis Losses:-Transformer Hysteresis Losses are caused because of the friction of the molecules against the flow of the magnetic lines of force required to magnetize the core, which are constantly changing in value and direction first in one direction and then the other due to the influence of the sinusoidal supply voltage. This molecular friction causes heat to be developed which represents an energy loss to the transformer. Excessive heat loss can overtime shorten the life of the insulating materials used in the manufacture of the windings and structures. Therefore, cooling of a transformer is important. Also, transformers are designed to operate at a particular supply frequency. Lowering the frequency of the supply will result in increased hysteresis and higher temperature in the iron core. So reducing the supply frequency from 60 Hertz to 50 Hertz will raise the amount of hysteresis present, decreased the VA capacity of the transformer.
Eddy Current Losses or iron loss :- Transformer Eddy Current Losses on the other hand are caused by the flow of circulating currents induced into the steel caused by the flow of the magnetic flux around the core. These circulating currents are generated because to the magnetic flux the core is acting like a single loop of wire. Since the iron core is a good conductor, the eddy currents induced by a solid iron core will be large. Eddy currents do not contribute anything towards the usefulness of the transformer but instead they oppose the flow of the induced current by acting like a negative force generating resistive heating and power loss within the core.
Copper Losses:- But there is also another type of energy loss associated with transformers called “copper losses”. Transformer Copper Losses are mainly due to the electrical resistance of the primary and secondary windings. Most transformer coils are made from copper wire which has resistance in Ohms. This resistance opposes the magnetizing currents flowing through them. When a load is connected to the transformers secondary winding, large electrical currents flow in both the primary and the secondary windings, electrical energy and power (or the I2 R) losses occur as heat. Generally copper losses vary with the load current, being almost zero at no-load, and at a maximum at full-load when current flow is at maximum.
EMF EQUATION OF THE TRANSFORMER
The transformer works based on the FARADAY'S LAWS OF ELECTROMAGNETIC INDUCTION.
The sinusoidal waveform of flux is given below
Change in flux d⍉=⍉ₘ-0=⍉ₘ
Change in time dt= T/4 sec
Average value of emf induced
(d⍉/dt)=⍉ₘ4/T........... (1)
and 1/T=f (frequency in Hz)
∴ Average emf induced per conductor =4f⍉ₘ volts............. (2)
For the N number of Conductors, the average emf =4f⍉ₘN volts
RMS value = 1.11×Average value (for sinusoidal signal)
RMS value of emf induced =4•44 f⍉ₘN
For primary side N =N₁
For secondary side N=N₂
Induced emf for primary side e₁= 4•44f⍉ₘN₁
Induced emf for secondary side e₂=4•44f⍉ₘN₂
For an ideal transformer in which there is no losses and no impedance drops V₁=e₁ and V₂=e₂ where V₂ is the terminal voltage.
VOLTAGE TRANSFORMATION RATIO (K)
It may be obtained as
e₂/e₁=N₂/N₁=K
The constant (K) is known as voltage transformation ratio.
N₂>N₁ i.e K>1 then the transformer is known as STEP UP transformer.
N₂<N₁ i.e K<1 then the transformer is known as STEP DOWN transformer.
Again for an ideal transformer INPUT V A = OUTPUT V A.
∴V₁I₁=V₂I₂
I₂/I₁=V₁/V₂=1/K
Hence currents are in the inverse ratio of the (voltage) transformation ratio.
TURNS RATIO OF THE COIL OF THE TRANSFORMER
The transformer turns ratio is the number of turns in the primary windings to the number of turns in the secondary windings.
N₁/N₂
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OPEN CIRCUIT & SHORT CIRCUIT TEST
OPEN CIRCUIT :-The purpose of the open circuit test is to determine the no-load current and losses of the transformer because of which their no-load parameter are determined. This test is performed on the low voltage winding of the transformer. The wattmeter, ammeter and the voltage are connected to their primary winding. The nominal rated voltage is supplied to the winding with the help of the ac source.
The other winding of the transformer is kept open. As the other winding of the transformer is open the no-load current flows through the L.V winding.
The value of no-load current is very small as compared to the full rated current. The copper loss occurs only on the primary winding of the transformer because the secondary winding is open. The reading of the wattmeter only represents the core and iron losses. The core loss of the transformer is same for all types of loads.
SHORT CIRCUIT :- The short circuit test is performed for determining the below mention parameter of the transformer. It determines the copper loss occur on the full load. The copper loss is used for finding the efficiency of the transformer. The equivalent resistance, impedance, and leakage reactance are known by the short circuit test.The short circuit test is performed on the secondary or high voltage winding of the transformer. The measuring instrument like wattmeter, voltmeter and ammeter are connected to the High voltage winding of the transformer. The other winding is short circuited by the help of thick strip of copper link which is connected to their terminal. The low voltage variable source is connected across the secondary winding because of which the full load current flows from both the secondary and the primary winding of the transformer. The full load current is measured by the ammeter connected across their secondary winding.
The low voltage source is applied across the secondary winding which is approximately 5 to 10% of the normal rated voltage. The flux is set up in the core of the transformer. The magnitude of the flux is small as compared to the normal flux.The iron loss of the transformer depends on the flux. It is less occur in the short circuit test because of the low value of flux. The reading of the wattmeter only determines the copper loss occur on their windings. The voltmeter measures the voltage applied to their high voltage winding. The secondary current induces in the transformer because of the applied voltage.
Just like any other electrical machine, efficiency of a transformer can be defined as the output power divided by the input power. That is efficiency = output / input . Transformers are the most highly efficient electrical devices. Most of the transformers have full load efficiency between 95% to 98.5%
Transformers are the most highly efficient electrical devices. Most of the transformers have full load efficiency between 95% to 98.5% . As a transformer being highly efficient, output and input are having nearly same value, and hence it is impractical to measure the efficiency of transformer by using output / input. A better method to find efficiency of a transformer is using, efficiency = (input - losses) / input = 1 - (losses / input).
efficiency of a transformer will be maximum when copper loss and iron losses are equal.
That is Copper loss = Iron loss.
All Day Efficiency Of Transformer
But in some types of transformers, their performance can not be judged by this efficiency. For example, distribution transformers have their primaries energized all the time. But, their secondaries supply little load all no-load most of the time during day (as residential use of electricity is observed mostly during evening till midnight).
That is, when secondaries of transformer are not supplying any load (or supplying only little load), then only core losses of transformer are considerable and copper losses are absent (or very little). Copper losses are considerable only when transformers are loaded. Thus, for such transformers copper losses are relatively less important. The performance of such transformers is compared on the basis of energy consumed in one day.
All day efficiency of a transformer is always less than ordinary efficiency of it.
APPLICATIONS OF THE TRANSFORMER
1)Most of the transformers are used in transmission and distribution systems i.e Electricity and Power utility Boards.
2)Applications in Automobile Industry:-Electric vehicles are the up and coming automobiles to create buzz in the market. Their batteries are charged by a power source. However, custom transformer is needed to monitor and control the voltage of electricity that is being used for charging the batteries. Advanced technology and innovations have led to development of “smart transformers” that can be used for charging multiple electric vehicles at a time.
3)Applications in the Steel Manufacturing Industry:-Steel manufacturing plants rely on the delivery of high currents over a varied range of voltages for their functioning. This requirement is fulfilled by specialized high voltage transformers. Such transformers can sustain the extreme dielectric, mechanical, and thermal constraints of a steel furnace.
4)Application in the Electrochemical Industry:-Electrolysis of elements like copper, aluminum, zinc or chlorine is essential in various electroplating processes. Rectifier transformers are specially designed to carry out such electrolysis process efficiently.
Apart from above mentioned industrial applications, electric transformers are also useful in following sectors:
a) Aerospace
b) Audio Systems
c) Military Subcontractors
d) Current Transformation
e) Biochemical and Biomedical
f) Communications
g) Data Processing
h) Clock and Timer Circuits
Based on the type of industrial application, you can select the best suited transformer to carry out the operations efficiently.
CONCLUSION
A transformer consists of two coils 1) primary winding and 2) secondary winding .
An ac voltage is put across the primary winding inducing a voltage in the secondary winding.
Transformers allow an ac signal to be transferred from one circuit to another circuit.
Transformers allow stepping up, stepping down, or passing the signal unchanged.
Transformers are designed to operate at certain frequencies.
The turns ratio determines whether a transformer is used to step up , step down ,or pass voltage unchanged.
The ratio of secondary to primary voltage is equal to the ratio of secondary to primary turns.
A transformer that produces a secondary voltage greater then its primary voltage is called step-up transformer.
The turns ratio of a step-up transformer is always greater then one.
A transformer that produces a secondary voltage less than its primary voltage is called step-down transformer.
The turns ratio of a step-down transformer is always less than one.
The amount of voltage is stepped-up or stepped-down is determined by the turns ratio.
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Click here for commentsThis article is too good and here all information ar so easy for understanding this topic...
ReplyThank you
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