1
GATE EE 2014 Set 3
+2
-0.6
The parameters measured for a 220V/110V, 50 Hz, single-phase transformer are:

Self inductance of primary winding = 45 mH
Self inductance of secondary winding = 30 mH
Mutual inductance between primary and secondary windings = 20 mH

Using the above parameters, the leakage (Ll1 , Ll2) and magnetizing (Lm) inductances as referred to primary side in the equivalent circuit respectively, are
A
5mH, 20mH and 40mH
B
5mH, 80mH and 40mH
C
25mH, 10mH and 20mH
D
45mH, 30mH and 20mH
2
GATE EE 2014 Set 3
+2
-0.6
The mean thickness and variance of silicon steel laminations are 0.2 mm and 0.02 respectively. The varnish insulation is applied on both the sides of the laminations. The mean thickness of one side insulation and its variance are 0.1 mm and 0.01 respectively. If the transformer core is made using 100 such varnish coated laminations, the mean thickness and variance of the core respectively are
A
30 mm and 0.22
B
30 mm and 2.44
C
40 mm and 2.44
D
40 mm and 0.24
3
GATE EE 2014 Set 3
+2
-0.6
An open circuit test is performed on 50 Hz transformer, using variable frequency source and keeping V/f ratio constant, to separate its eddy current and hysteresis losses. The variation of core loss/frequency as function of frequency is shown in the figure The hysteresis and eddy current losses of the transformer at 25 Hz respectively are
A
250 W and 2.5 W
B
250 W and 62.5 W
C
312.5 W and 62.5 W
D
312.5 W and 250 W
4
GATE EE 2014 Set 3
Numerical
+2
-0
The load shown in the figure absorbs 4 kW at a power factor of 0.89 lagging. Assuming the transformer to be ideal, the value of the reactance X to improve the input power factor to unity is ___________.