Instrument Transformer and Uses

What is Instrument Transformer and how does it work?

The Instrument transformers are as same as other conventional transformers but different it is just high accuracy class electrical devices. Instrument transformers are actually used to isolate or transform voltage or current levels for using metering or controlling signals. 

Operating the instruments for controlling the system or measuring the high-level voltage or current, the instrument transformers are used to decrease to voltage or current level to measuring level for safely isolating secondary control circuitry from the high voltages or currents. 

Using of Instrument Transformer

So, if you ask what is Instrument Transformer is, In simple, we can say the Instrument Transformers are used in AC systems for the measurement of electrical quantities like- voltage, current, power, energy, power factor, frequency. Instrument transformers are also used with protective relays for the protection of the power system.

Instrument transformer Connection Procedure

The high voltage or high current end of the circuit is connected to the primary winding of the instrument transformer and the meter or relay is connected to the secondary circuit.

Instrument transformer Connection Procedure

Types of Instrument Transformers

Instrument transformers are of two types –

  1. Current Transformer (C.T.)
  2. Potential Transformer (P.T.)
Read more details on Current Transformer 

Read more details on Current Transformer 

Difference between C.T. and P.T.

Sl. No.Current Transformer (C.T.)Potential Transformer (P.T.)
1Connected in series with power circuit.Connected in Parallel with Power circuit.
2The secondary is connected to Ammeter.The secondary is connected to Voltmeter.
3Secondary works are almost in short-circuited condition.Secondary works are almost in open-circuited condition.
4The primary current depends on the power circuit current.The primary current depends on the secondary burden.
5Primary current and excitation vary over a wide range with the change of power circuit currentPrimary current and excitation variations are restricted to a small range.
6One terminal of the secondary is earthed to avoid the insulation break down.One terminal of secondary can be earthed for safety.
7The secondary is never open-circuited.Secondary can be used in open circuit conditions.

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