Question

The observation when the secondary winding of a current transformer is open-circuited is?

(a) The whole of the primary current produces a large value of flux in the core thereby producing a large voltage in the secondary winding

(b) The large voltage may act as a safety hazard for the operators and many even raptures the insulation

(c) When the large magnetizing force is taken off, it leaves a large value of residual magnetism

(d) When the large magnetizing force is taken off, it leaves a small value of residual magnetism

This question was posed to me in exam.

I'm obligated to ask this question of Advanced Problems on C.T. and P.T. topic in division Extension of Instrument Ranges of Electrical Measurements

Answer 1

Right answer is (b) The large voltage may act as a safety hazard for the operators and many even raptures the insulation

Easy explanation: Never open the circuit of the secondary winding of a current transformer while to the primary winding is energized. Failure to observe this precaution may lead to serious consequences both to the operating personnel and to the transformer.