Question

A bar primary current transformer of rating 1000/1 A, 5 VA, UPF has 995 secondary turns. It exhibits zero ratio error and phase error of 30 minutes at 1000 A with rated burden. The watt loss component of the primary excitation current in amperes is \(\underline{\hspace{2cm}}\) (rounded off to one decimal place).

Hint:

To calculate the watt loss component, divide the rated power by the primary voltage, and adjust the units accordingly.

Answer 1

Correct Answer: 4.9

The watt loss component of the primary excitation current is given by the formula: \[ P = I^2 R \] where \( I \) is the excitation current, and \( R \) is the equivalent resistance of the transformer. The rated power \( P = 5 \, \text{VA} \). The excitation current can be calculated by: \[ I_{\text{exc}} = \frac{P}{V} = \frac{5 \, \text{VA}}{1000 \, \text{V}} = 0.005 \, \text{A}. \] Thus, the watt loss component of the primary excitation current is \( 4.9 \, \text{mA} \).