Question

Following are the test results for the 4KVA, 200/400V, 50Hz, single phase transformer. O.C test : 200V, 0.8A, 70W S.C test : 17.5V, 9A, 50W. Calculate the parameters of equivalent circuit of a transformer.

Answer 1

From the open circuit test we get,

R₀ = V²/P

= 200²/70

= 571.4 ohms

CosФ = W/VI

=70/200*0.8

=70/160

=0.4375

=> sinФ = 0.894

Therefore

Iμ = I sinФ = 0.715

Iw = I cosФ = 0.35

hence,

X₀ = V/Iμ = 200/0.715 = 279.72

In the short circuit test :

W = I²R

=> R = W/I²

=50/9²

= 0.617 ohms

Z = V/I

= 17.5/9

= 1.94

X² = Z² - R²

= 3.78 - 0.38

=> X²  = 3.4

=> X = 1.84