What is the function of fuses in Instrument Transformers?

Instrument Transformers are sometimes provided with fuses. These fuses are intended to isolate the transformers in the event of internal fault.

Opinion is divided over the use of these fuses. Maloperation of these fuses can cause large scale disruption of power systems by way of unintended operation of the relays that are connected to the instrument transformers. Hence, some manufacturers provide fuses in the instrument transformers only when specifically requested.

While, the fuses cannot protect the instrument transformers from burnout during normal operation as the burnout current may be extremely low, they can ensure that a fault inside the transformers does not impact the busbar or generator in which it is mounted.

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