Different Types of Transformers and Their Applications

There are four main types of transformers viz.

• Distribution Transformers
• Power Transformers
• Autotransformers
• Instrument Transformers

Distribution Transformers

The transformers which are used to step down the transmission voltage to the distribution voltage or the distribution voltage to a standard service voltage are known as distribution transformers. These transformers have variable load which is considerably less than the full load rating of the transformer. Hence, the distribution transformers are designed to have their maximum efficiency at between ½ and ¾ of the full load.

These transformers are kept in operation 24 hours a day whether they are carrying any load or not. The distribution transformers have a good voltage regulation and are designed for a small value of leakage reactance.

Power Transformers

Power transformers are used in generating stations and substations at both ends of the power transmission lines for step-up or step-down the voltage. These transformers are operated during the load periods and are disconnected during light load periods.

Power transformers are designed to operate with an almost constant load which is equal to their full load rating i.e. they are designed to have maximum efficiency at or near full load. This means that full load variable losses must be equal to the constant losses. Power transformers are designed to have considerably higher leakage reactance. For power transformers, the voltage regulation is less important as compared to the current limiting effect of higher leakage reactance.

Autotransformer

An autotransformer is a one winding transformer in which a portion of the winding is common to both the high voltage and low voltage sides. The autotransformer is used in the applications where the transformation ratio (K), either step-up or stop-down, differs little from unity.

For the same ratings, an autotransformer requires less conductor material than an ordinary two winding transformer. The autotransformers are used for starting induction motors and in boosters for rising the voltage of feeders.

Instrument Transformers

The instrument transformers are used to reduce the high voltages and currents to safe and practical values which can be measured by using conventional instruments (voltmeters and ammeters). The instrument transformers facilitate the AC measurement with low range AC instruments.

There are two types of Instrument Transformers viz.

• Current Transformer (CT) – A current transformer is the one which is used for the transformation of current from a higher value to a lower value so that it can be measured with a low range AC ammeter.
• Potential Transformer (PT) – The potential transformer can be defined as an instrument transformer which is used for the transformation of the voltage from a higher value to a lower value so that the high alternating voltage can be measured with a low range AC voltmeter. The PT should be designed so that the variation in the voltage ratio with the load is minimum and also, the phase between the input and output voltages is minimum.

Applications of Transformers

The transformers are used in several applications such as

• To change the voltage level and current level in the electrical power systems.
• As a coupling device.
• To isolate one circuit from the other electrically, as the primary and secondary are electrically isolated.
• To measure the currents and voltages in the form of instrument transformers.
• As impedance matching device.