Electrical Engineering ⇒ Topic : Instrument Transformers

INSTRUMENT TRANSFORMERS

Instrument transformers are generally used to extend the range of ac instruments like ammeters,voltmeters, wattmeters, VAR meters. They have the following advantages: (i) They serve to isolate the measuring instrument from high voltages ensuring safety to both the instrument and the operating personnel, and (ii) The circuits need not be disturbed for measurement purposes.Instrument transformers are of two types: (i) Potential transformer, and (ii) Current transformer.

Instrument Transformers

For measuring a large current in a d.c. circuit, we use low-range ammeter with a suitable shunt. The measurement of high d.c. voltage is made using a low-range voltmeter with a multiplier.However, this method is not used for the measurement of high alternating currents and voltages for many good reasons. In order to measure high alternating currents and voltages, we employ specially designed transformers, called instrument transformers. These transformers facilitate the a.c. measurements with low-range a.c. instruments. There are two types of instrument transformers viz.

(i) Current transformers

(ii) Potential transformers