Power systems miscellaneous Difficult Questions and Answers

Power systems miscellaneous

If a 100V/10V, 50 VA transformer is converted to 100/110V auto transformer, then rating of the auto transformer is _______ VA

Correct Option: D

A transformer rated for 500 kVA. 11 kv/0.4 kV has an impedance at 10% and is connected to an infinite bus. The fault level of the transformer is ___________ kVA

Correct Option: B

A 100/5 A bar primary current transformer supplies an O/C relay set at 25% pick up and it has a burden at 5 VA. The secondary voltage is _________V

Correct Option: A

If the inductance and capacitance of a system are 1 H and 0·01 μF respectively and the instantaneous value of current interrupted is 10 amps. The value of shunt resistance across the breaker for critical damping is ________ kΩ

For critical damping,

R = 0.5 √	L	= 0.5√	1	= 5 kΩ
	C		0.01 × 10^-6

Correct Option: C

For critical damping,

R = 0.5 √	L	= 0.5√	1	= 5 kΩ
	C		0.01 × 10^-6

If the inductance and capacitance of a system are 1·0 H and 0·01 μF respectively and the instantaneous value of current interrupted is 10 amp, the voltage across the breaker contacts will be __________ kV

v = i_a √	L	= 10√	1	= 100 kv
	C		0.01 × 10^-6

Correct Option: B

v = i_a √	L	= 10√	1	= 100 kv
	C		0.01 × 10^-6