The Difference Between a Current Transformer and a Voltage Transformer?

What are transformers?

The purpose of a transformer is to enable electrical energy to move between two circuits through a process of electromagnetic induction. In doing this, transformers can increase or decrease the voltage or current that passes through electric power applications. It makes it possible to measure the current and voltage safely in a circuit that has a very high level of amperes and volts passing through it.


A transformer consists of a primary winding, a core and secondary winding. Wrapped around each of the windings are turns of copper wiring. In the electromagnetic induction process, it is these turns that help alter the voltage. Being able to increase or decrease the levels passing through circuit’s means that power networks can change AC voltages safely from one voltage level to another.

When it comes to current transformers, these work with currents while voltage transformers involve voltages. In both instances, these types of transformers are known as instrument transformers.

Voltage Transformers

As its name implies, a voltage transformer is a device that works with voltages. This device makes it possible to increase (step up), decrease (step down) or transfer an electrical current between circuits. The use of these devices may be more likely in high-voltage situations where it is necessary to control the voltage. That said a voltage transformer also appears in many low-voltage electronic devices.

Irrespective of the type of transformer, the device can change the voltage from one level to another due to the number of turns of copper wiring on each winding. It is the number of turns on the windings that determine whether the voltage is increased, decreased or stays the same. Whatever the type of transformer the loss in net power that occurs during the process is minimal.

Current Transformers

If a current is too high, it can make measuring it directly challenging. The same can apply if the voltage of the circuit is too high. In either case, this is where a current transformer comes in handy. They make it possible to reduce high voltage currents to a much lower and safer level. As a result, they provide a way of being able to monitor the actual electrical current that is flowing through a circuit using a standard ammeter. It can do all of this due to the turns on the windings of a current transformer. While a current transformer it will have a large number of turns on its secondary winding, the primary winding has only one. So that it can carry a full load current the primary winding is usually connected in a series so that it can handle the full electrical current.

One area where you can see current transformers is in high-voltage electrical substations and the national grid. To safely manage such large currents these devices provide the necessary protection, measurement and control required. It can do this by keeping the measurement and control circuitry separate from the high voltages that pass through circuits used in the transmission of power.

What are the differences?

While there are things that are similar there are also differences between a voltage transformer and a current transformer. Some of the differences include:

  • A current transformer uses a current while it is voltage that passes through a voltage transformer.
  • Voltage transformers decrease the voltage level by increasing the current that passes through the secondary winding. Current transformers, on the other hand, lower the current by increasing the voltage.
  • The primary winding on a voltage transformer can have several turns whereas it has only one turn in a current transformer.
  • It is possible to use a current transformer rather than an ordinary ammeter to measure the value of currents passing through high voltage power applications. When it comes to voltage transformers, it is possible to use them as either high voltage voltmeters or ordinary voltmeters.

In addition to the above, where there is a need to undertake measurements in the same line in three phase power transmission it is necessary to use three current transformers. With a voltage transformer the difference is that instead of three, only a single transformer is required.

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