Question

A current transformer has a single turn on the primary winding and a secondary winding of 60 turns. The secondary

winding is connected to an ammeter with a resistance of 0.15Ω. The resistance of the secondary winding is 0.25Ω. If

the current in the primary winding is 300 A, determine (a) the reading on the ammeter, (b) the potential difference

across the ammeter and (c) the total load (in VA) on the secondary.

Answer 1

A) the reading on the ammeter

We know that

N₁I₁ = N₂I₂

I₂ = (N₁I₁)/N₂

= (1*300)/60

= 5 A

Hence reading of ammeter = I_m = I₂ = 5 A

B) the potential difference

I_mR_m = 5 *0.15

= 0.75 v

Hence V_m = 0.75 v

C)  the total load (in VA) on the secondary.

= V₂I₂

= (I₂(R₁+R_m))I₂

= 5 (0.25+0.15) *5

= 5*0.4*5

S = 10 VA