Introduction to Instrument Transformers

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Introduction to Instrument Transformers

Instrument transform are widely are used in protection circuits of power system for the operation of over current, under voltage, each fault and various other types of relays. Transformers used in addition with the measuring instruments for measurement purposes are called “Instrument Transformers”.

Types of Instrument Transforms

There are two types of instrument transformer:

1. Current Transform (CT):

It is used for the measurement of current.

2. Potential Transform (PT):

It is used for the measurement of voltage. It is also called voltage transform. Below Figures show both types of instrument transforms.

Current Transformer Diagram

Advantages of Instrument Transformers

Instrument transformers are widely used for the precise and routine measurement of voltage and current because of the following advantages:

• Several instruments can be operated from a single instrument transformer (CT or PT).
• The measuring circuit is isolated from the high voltage power-circuit which ensures safety of the operator.
• There is low power consumption in the measuring circuit.
• The replacement of instrument transformer is earlier.
• Instrument transformers are used for the measurement of large magnitude of current and voltages.
• Instrument transformers produce practically the same instrument reading regardless of the constants of the instruments.