Question

Ratio error in a P.T. depends on _________

(a) secondary current

(b) primary voltage

(c) secondary current

(d) turns ratio

I have been asked this question in an interview for internship.

The doubt is from Reduction of Errors in Potential Transformers in section Extension of Instrument Ranges of Electrical Measurements

Answer 1

The correct answer is (c) secondary current

The best I can explain: In a P.T., the difference between actual ratio and turns ratio is given by the relation,

where, R is the ratio error

       n is the turns ratio

       Is is the secondary winding current

       Ie is the iron loss component

       Im is the magnetising component

It is seen from the above equation that the ratio error in a P.T. depends on the secondary current, magnetising and iron loss components of current.