Table of Contents
Definition of Transformer | Definition of transformer
The device that gives it more or less voltage, without changing the frequency and power given to it. That stationary device is called a transformer. Through a transformer, the frequency and power of one circuit is transferred to another circuit by maintaining the same frequency and power.
Why do we need a transformer?
The 3 phase supply system has more advantages over the single phase supply system. Therefore, generation, transmission and distribution of 3 phase supply systems are done nowadays. In order to make this supply system more efficient, the Indian Standards Association has fixed a standard voltage for each stop.
Generation Voltage = 11 KV.
Transmission Voltage = 440 KV, 220 KV
Distribution Voltage = 132KV, 66KV, 33KV, 11KV
Utilisation Voltage= 440 V or 230 V
If this voltage limit is understood carefully, then 11000 volts which is generated, and the voltage directly reaching the customers which is used by the customers. That is 3 phase 440 volt and single phase 230 volt.
From all this we understand that only 11000 volts created are reduced to 440 volts and 230 volts.
In this way, while reducing the high voltage in the AC supply system or increasing the low voltage, its supply frequency and power should not change. The device required for this is a transformer.
Why is a transformer called a stationary device?
No part in the transformer is rotating or making noise like a motor. That’s why a transformer is called a stationary device.
On what principle does a transformer work?
Transformer works according to the Self or Mutual Induction element of Electromagnetic Induction.
Means when another coil is kept stationary in a changing magnetic field. Then those changing magnetic lines get cut due to the conductor of the coil kept stationary. And because of this, EMF is created in the coil kept stationary according to Ferede’s Element of Electromagnetic Induction.
Simple Structure of Transformer
There are mainly two main parts in the composition of the transformer, the core and the winding.
Chore It is made up of L type, E type, I type or rectangular shaped steppings of English. These steppings are made of silicon steel as thick as 0.35 mm to 0.5 mm.
Many such steppings are insulated from each other to form a laminated core. Silicon steel is used to make the core. Because it reduces the hysteresis loss. And by making a laminate, the eddy current loss is reduced.
The primary and secondary winding is done by insulating from the core on the transformer core mentioned above. The winding to which the supply is given is called the primary winding.
The winding from which supply is taken for the load is called secondary winding. The way the windings are insulated from the core. Similarly, the primary winding and the secondary winding are also insulated.
Working of Transformer | How does a transformer work?
When AC supply is given to the primary winding of the transformer. Then changing magnetic lines are formed around the primary winding. Due to changing magnetic lines, they are cut off from the stationary conductor.
And self induced EMF is created in the primary winding. AC current flows through the primary winding, due to which changing flux is created around the primary winding.
The primary flux flows through the core and reaches the secondary winding. Mutual Induced EMF is created in the secondary winding by taking cutting action between the flux and the turns of the secondary winding.
According to Faraday’s second law of electromagnetic induction, the induced EMF produced is proportional to the turns of the winding. Meaning, the more turns in the winding, the more the cutting action, the more static EMF is created.
When the secondary winding is connected to the load, then the circuit of the secondary is completed and current starts flowing through the winding. And thus electric power is provided to the load. This is how the transformer works.
Types of Transformer on the basis of construction
On the basis of the composition of the core of the transformer, there are 3 types of transformers.
- Core Type Transformer
- Shell Type Transformer
- Berry Type Transformer
Core Type Transformer
As shown in the figure, the steppings of the core of a core type transformer are L type. All steppings are laminated to each other. On the core where the primary and secondary winding is done. There both the windings are also insulated from each other. The partner itself is also insulated from the core. The windings on this core are done one after the other in this way. The windings are shown separately from each other in the figure so that you can understand easily. But in reality both the indices are on top of each other.
In such a core, there is only one path for the flux to flow. Because of this, the proof of leakage flux is very less in it. This type of core has a longer average length, but has a smaller cross-sectional area. So more turns have to be done on this core. This transformer is used for High Output Voltage.
Shell Type Transformer
As shown in the figure, the steppings of the core of a shell type transformer are E type and I type. All steppings are laminated to each other. Between the core where the primary and secondary winding is done. There both the windings are also insulated from each other. And both these inductions primary and secondary are done one after the other.
While winding on the core, first the primary winding is done, then after that the secondary winding is done on the primary winding. Doing so reduces the proof of leakage flux. There are 2 routes for the flux to flow in the core of this transformer. Since the winding is located on the middle limb, it is more prone to leakage flux. Shell type transformer cores have less average length, but larger cross-hole area, so fewer turns have to be done on this core.
This transformer is used for low output voltage. Shell type transformer is used in most of the single phase transformers.
Berry Type Transformer
It is also called a distributed core type transformer. as shown in Figure. The core of a Berry type transformer is made up of a rectangular disc. A group of one side of each disc is made and the winding is done on that group.
The number of steppings in a Berry type transformer, the number of paths to drain the flux.
Problems in Berry Type Transformer
- The construction of a Berry type transformer is a bit confusing.
- Its maintenance is also a bit difficult.
- Winding is difficult.
- Leakage proof is high.
For this reason, Berry type transformers are not very popular.
What is the difference between a core type transformer and a shell type transformer?
Core Type Transformer
Shell Type Transformer
There is only one way for the flux to flow.
Winding takes place on the limb on the days of the core.
Since the winding is on the outside, it helps to keep the winding cool from outside air.
The average length of the core is more.
The area of the hole cut across the core is less.
Less proof of leakage flux.
The winding being on the outer limb is easily visible, and easy to maintain.
It is suitable for high voltage.
There are two routes for the flux to flow.
There is a winding on the middle limb.
Since the windings are at the middle limb, the core is cooled.
The average length of the core is short.
The area of the hole cut across the core is more. Hence there are fewer turns.
Evidence of leakage flux is high.
Difficult to repair. And the winding is easy.
Suitable for low voltage.
How many types of transformers are there according to voltage?
There are 2 types of transformer to increase or decrease the voltage.
- Step Up Transformer
- Step Down Transformer
Step Up Transformer
The transformer which converts the voltage given to its primary winding into higher voltage and gives output voltage, that transformer is called Step Up Transformer.
Its composition is core type or shell type. The winding turns of a step up transformer are more secondary than primary. Because of this the flux of the primary is cut off by more turns of the secondary. Due to the action of mutual induction in the secondary winding, more voltage is created. Due to the high voltage of the secondary, the current of the secondary is low.
Therefore, the primary winding has fewer turns and a thicker wire. And the secondary winding is of more turns and less thick wire.
Step Up Transformer is used at the place where the voltage has to be increased.
Step Down Transformer
The transformer which converts the given voltage to its primary winding and gives output voltage, that transformer is called Step Down Transformer. The composition of this transformer is also core type or shell type. The primary of a step down transformer is of less thick wire and of more turns. The secondary is made of low turns and thick wire.
This transformer is used to reduce the voltage.
Instrument Transformer It is a type of step up transformer or step down transformer. But a short range voltmeter or ammeter is connected to its secondary winding. It is used to measure the current and voltage of HT Line. A Current Transformer (CT) is used to measure the current of the HT Line and a Potential Transformer (PT) is used to measure the voltage.
Current Transformer- CT
It is a step up transformer. As shown in the figure. The primary winding of a current transformer is of thick wire and of short turns (one or two turns in many places only one turn key). The primary winding of the current transformer is connected in series with the HT line. The secondary winding is of fine wire. And there are more turns. A flame range ammeter is connected at the end of the secondary winding, one side of which is earthed. Ammeter is of low range interest, but its scale is divided according to the ratio of the transformer.
Working of Current Transformer
Due to the primary HT line of the current transformer being in series, the entire current flows through the primary winding. Because of this flux builds up around the primary. The flux created in the primary is cut off from the turns of the secondary ends. Due to the high turns of the secondary, high voltage builds up in the secondary. But the current of the secondary is less than the proof of the ratio of the transformer. This low current flows through the ammeter. The current flowing in the ammeter is really small but the scale of the ammeter is divided according to the ratio of the transformer. Because of which we get the reading of the actual current flowing through the HT Line on the ammeter. In this way, it is easy to measure HT Line’s High Current Low Range ammeter. Which is impossible without a current transformer. Because if a short range ammeter is used at high current, it will burn. Therefore The current of the HT Line is reduced before the current transformer. And then it is measured with a low range ammeter.
Why is the secondary side of a current transformer earthed?
If the secondary winding of the current transformer is opened due to some reason, then no current flows through the secondary. Because of this flux does not build up in the secondary. Now at this time, due to the absence of flux opposing the primary flux, more and more flux starts flowing through the core. High Voltage is manufactured in the secondary. Due to high voltage, the insulation between the core and the winding starts to deteriorate. The core of the current transformer gets very hot. Due to excessive heat, the magnetic property of the core disappears forever. And sometimes after some time there is also a possibility of a current transformer blast. If this should not happen, because of this, the secondary winding of the current transformer is never kept open. The circuit of the secondary winding is always kept closed by adding a low range ammeter to the secondary side. One side meaning is given to it.
There is always a possibility of suddenly opening the secondary winding due to some fault in the ammeter or due to some other reason. Due to this, the above mentioned risk occurs to the current transformer. Therefore, even after adding an ammeter to the secondary, one side of it is always earthed. Whenever the ammeter is removed from the circuit, the secondary side is shorted. So that the circuit is always closed.
Potential Transformer (PT)
Potential Transformer This is a step down transformer. The turns of the secondary winding are of thick wire and of lesser turns. This is a Shell Type Transformer. As shown in figure, the primary winding of PT is of fine wire and more turns. The primary winding of the potential transformer is parallel to the HT line. A low range voltmeter is connected at the end of the secondary winding. (Generally the voltage of the secondary is stepped down to 110 V.)
Working of Potential Transformer (PT) | How does a Potential Transformer (PT) work?
The primary winding of the potential transformer PT is connected parallel to the HT line. The flux of the primary is cut off from the turns of the secondary winding. Due to the low voltage of the secondary, less voltage builds up in the secondary. This low voltage gets to the voltmeter connected to the secondary. In fact the voltmeter gets less voltage. But the scale of that voltage is divided according to the ratio of the transformer. Therefore, the reading received on the voltmeter appears to be equal to the actual voltage of the HT line at that time. In this way, the High Voltage of HT Line is easily measured with a low range voltmeter.