Voltage Transformer Working Principle

Voltage Transformer Working Principle

A transformer is an electronics device that can convert electrical energy from one circuit to another without changing the frequency of electricity. It can determine the rate of increase or decrease in proportion to the current rating of the load.

Using magnetic induction, the transformer performs the primary function of its operation. This principle is known as Faraday’s “law of electromagnetic induction.”

There is always a need to maintain a specific voltage in the transmission line and the distribution line. Voltage transformers are used to measure these high voltages. This blog will discuss how a voltage transformer works and the basic principles of its operation.

Voltage Transformer Working Principle
Voltage Transformer

Basic Construction of Voltage Transformer

A transformer consists of primary and secondary windings. The initial voltage of a step-down transformer is higher than the secondary voltage, and the number of turns of the primary winding is higher than that of the secondary winding.

The opposite is true of step-down transformers. The conductors used in the windings are more prominent in size to accurately measure the voltage, and the windings are capitalized to reduce the leakage response.

The design for the construction of the transformer should be the most efficient to achieve high accuracy of measurement. The windings of the high voltage rating (above 7kV) transformers are immersed in the oil-filled tank. The oil acts as a good insulator.

The magnetic core of the transformer is made of silicon lamination. The type of magnetic shell or core of a transformer is usually determined based on the type used. Cotton or paper is used as insulation in secondary windings. The oil-filled bushing connects to the source and loads to the tank.

Working Principle of a Voltage Transformer

Voltage must always be measured on the transmission line and the distribution line. A sudden increase or drop in voltage can lead to a significant accident. Electricity is transferred by magnetic induction from one winding to another winding in the transformer.

A transformer consists of two or more windings. Primary windings are connected with the source, and secondary windings are connected with the load.

There are three kinds of voltage transformers. Electromagnetic (a), Capacitor (b), and Optical (c). The basic working principle of these kinds of transformers information is given below:

We know the transformer has primary and secondary windings. The voltage is measured across the transmission line with the initial winding of the transformer. The transformer is connected in series with the current line. A range voltmeter can easily measure volts up to 0-110V. A portion of the transformer winding is grounded with the ground to ensure safety.

The voltage of a transmission or distribution line is usually determined by measuring the small voltage obtained in the transformer’s secondary. The output can be easily extracted using a formula. The formula is, Np /Ns = Vp /Vs=Is /Ip.


  • Vp= Primary Voltage
  • Vs= Secondary Voltage
  • Np= Number of the primary winding
  • Ns= Number of the secondary winding
  • Ip= Primary Current
  • Is= Secondary Current

If a potential transformer has a voltage ratio of 1000:10, the voltage measured at the primary Vs. is 100V. What is the secondary or high voltage line Vp is?

According to the question,

Np= 1000
Ns= 10
Vs= 100
Vp= ?

Solution: Np /Ns = Vp /Vs

Vp= (Np*Vs) /Ns= (1000*100) /10 =10,000= 10kV

The voltage transformer protects against significant losses by measuring the voltage and balancing the transmission and distribution lines. So voltage transformers are used in transmission and distribution lines. Sometimes it can give wrong readings.

So it is necessary to check the voltage transformer regularly. Due to the small size of the voltage transformer, its construction and operation costs are much lower than other transformers.


About the Author: Mehedi Hasan

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