Question

The primary of 400/1 A, 10 VA, 0.8 p.f, current transformer (C.T.) carries a current of 200 A. If the secondary current is measured to be 0.495 A, then the value of percentage ratio error will be

• A. $-1.50\%$
• B. $+1.50\%$
• C. $-0.99\%$
• D. $+0.99\%$

Answer 1

The correct option is C $-0.99\%$

Given,
Nominal ratio,

$K_n=\frac{400}{1}=400$

Actual transformation ratio,

$R=\frac{200}{0.495}=404.04A$

Percentage ratio error

$=\frac{\left(\text{Nominal ratio - Actual ratio}\right)}{\text{Actual ratio}}\times 100$

${ϵ}_r=\frac{400-404.04}{404.04}\times 100=-0.99\%$