Question

For a C.T. the nominal ratio is given by which of the following relation?

(a) Kn = \(\frac{I_{p(rated)}}{I_{s(rated)}}\)

(b) Kn = \(\frac{I_{s(rated)}}{I_{p(rated)}}\)

(c) Kn = \(\frac{1}{I_{s(rated)}}\)

(d) Kn = Ip(rated)

I have been asked this question in semester exam.

The question is from Ratios of Instrument Transformers in portion Extension of Instrument Ranges of Electrical Measurements

Answer 1

Correct answer is (a) Kn = \(\frac{I_{p(rated)}}{I_{s(rated)}}\)

For explanation I would say: In a current transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current.

Kn = \(\frac{I_{p(rated)}}{I_{s(rated)}}\)

where, R is the transformation ratio

       Ip(rated) is the rated primary winding current

       Is(rated) is the rated secondary winding current.