1
GATE EE 1999
MCQ (Single Correct Answer)
+2
-0.6
The percentage resistance and percentage reactance of a 10 kVA, 400 V/200 V, 3-phase transformer are 2% and 10% respectively. If the constant losses in the machine are 1%, the maximum possible percentage efficiency of the transformer is:
A
98.32
B
97.25
C
96.25
D
96.12
2
GATE EE 1999
MCQ (Single Correct Answer)
+2
-0.6
A 10 kVA, 400 V/200 V single-phase transformers with 10% impedance draws a steady short circuit line current of
A
50 A
B
150 A
C
250 A
D
350 A
3
GATE EE 1999
MCQ (Single Correct Answer)
+2
-0.6
The windings of a Q kVA, $$\frac{V_1}{V_2}$$ Volt, three-phase, Delta connected, core type transformer are reconnected to work as a single phase transformer. The maximum voltage and the power ratings of the new configuration are,
A
$$\frac{3V_1}{3V_2},\;3Q$$
B
$$\frac{V_1}{V_2},\;Q/3$$
C
$$\frac{\sqrt3V_1}{\sqrt3V_2},\;2Q$$
D
$$\frac{\displaystyle\frac32V_1}{\displaystyle\frac32V_2},\;\frac Q2$$
4
GATE EE 1998
MCQ (Single Correct Answer)
+2
-0.6
A 50 Hz transformer having equal hysteresis and eddy current losses at rated excitation is operated at 45 Hz at 90% of its rated voltage. Compared to rated operating point, the core losses under this condition:
A
reduce by 10%
B
reduce by 19%
C
reduce by 14.5%
D
remain unchanged
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