Question

What is the effect of reducing the secondary turns in a C.T. by 1%?

(a) transformation ratio reduces by the same value

(b) no effect

(c) nominal ratio increase by the same value

(d) secondary current increases by the same value

The question was asked by my college professor while I was bunking the class.

The question is from Design Features of Current Transformers topic in portion Extension of Instrument Ranges of Electrical Measurements

Answer 1

The correct option is (a) transformation ratio reduces by the same value

Explanation: In a C.T., the transformation ratio is given by

R = n + ^Ie⁄Is

where, n is the turns ratio

            Ie is the core loss component of the excitation current

       Is is the secondary winding current

As the number of secondary turns is reduced by a factor of 1%, the transformation ratio (R) is reduced by approximately the same percentage.