Potential Transformer [Explained] in Detail

What is potential transformer ?

The potential transformer is also known as an instrument transformer. Generally, is it used for alteration of voltage right from a higher value to a lower one. In simple words, we can say that a potential or voltage transformer is used to lower down the higher values of the voltage to a safer lever in order to measure currents as well as voltage associated with power transmission and distribution systems. Once stepping down of voltage to a safer value is done by the voltage transformer, voltage can be easily measured by using devices like voltmeter, watt-hours meters and wattmeter etc. Due to this property, sometimes, it is also considered as ‘step-down’ voltage transformer.

potential transformer

Apart from lowering down voltage, a potential transformer also helps in protecting the main circuit during high voltage supply. A simple transformer cut the level of current to the relay or instrument operating range. On the other hand, a potential transformer converts the high voltage to a circuit operating voltage level.

potential transformer Sketch

Construction and working of potential transformer

The basic or you can say that primary winding of the potential transformer are joined with the high voltage power circuits amid two phases and ground. This connection depends on the voltage transformer rating as well as their uses. On the other hand, the secondary winding or you can say that rest winding of the potential transformer is connected with the several measuring devices along with electrical relays. Both, primary as well as secondary windings are magnetically coupled with each other. The secondary winding has very few coil turns as compare to the primary winding. Actually, the number of coil turns in both secondary and primary winding depends upon the work for which the instrument transformer is used.

potential transformer Sketch

A potential transformer comes in two types of rating i.e. primary and secondary rating. The primary rating of the transformer ranges from 400 V to several hundred volts. And the secondary rating of most of the transformers are 110 V. the ratio in between these two ratings are known as transformation or turn ratio.

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Applications of potential transformer

  1. They are used at several places like large scale industries, school, colleges, hospitals etc. the general purpose of using it at such places is to metering voltage.
  2. Sometimes, potential or voltage transformers are also used for the protection of the feeders.
  3. Potential transformers are also used for synchronizing the feeders as well as generators.
  4. It is also used for the protection of the impedance of the generators.
  5. They are are used for protecting relying scheme.

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Types of potential transformer

These transformers are Mainly classified in two types, i.e. the capacitor voltage and the conventional wound potential transformer. These two types of instrument transformers comes in outdoor potential transformer category. Outdoor potential transformers comes in three or single phase for different purposes such as metering and relaying applications. Both types of transformers are explained at below

Conventional wound potential transformer

In this type of transformer, there is a use of insulation that makes it very expensive.

Capacitor potential transformer

The type of potential transformer is made by combining magnetic potential transformer as well as capacitor potential divider in very small ratio.

Apart from above mentioned types, potential transformer has one other type, i.e. indoor potential transformer. Like outdoor, indoor potential transformers also come in three or single phase which were molded with the help of magnetic field.

Feel free to ask any question or you may suggest any improvements as well !

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This article has 2 comments

  1. Sodoka Reply

    Is the potential transformer is simply an step down transformer ? Also Does measuring voltage uses the low capacity voltmeter with the calibrated reading ?

    • Farhan Sheikh Ahmad Reply

      Yes precisely. They are just the step down transformers with the low capacity voltmeter which are calibrated in order to measure the high quantity of voltage.

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