Question

Phase angle in a C.T. is defined as ____________

(a) \(\frac{180}{π} [\frac{I_m cosδ}{nI_s}]\) degrees

(b) \(\frac{180}{π} [\frac{I_c sinδ}{nI_s}]\) degrees

(c) \(\frac{180}{π} [\frac{I_m cosδ – I_c sinδ}{nI_s}]\) degrees

(d) \(\frac{180}{π} [\frac{I_m sinδ – I_c cosδ}{nI_s}]\) degrees

I had been asked this question during an online interview.

My doubt is from Errors in Current Transformers in section Extension of Instrument Ranges of Electrical Measurements

Answer 1

The correct choice is (c) \(\frac{180}{π} [\frac{I_m cosδ – I_c sinδ}{nI_s}]\) degrees

For explanation I would say: During power measurement, there exists phase angle error in a C.T. The phase angle is defined as

Phase angle = \(\frac{180}{π} [\frac{I_m cosδ – I_c sinδ}{nI_s}]\) degrees.

where. Im is the magnetising component of the excitation current

       Ic is the core loss component of the excitation current

            Is is the secondary winding current.