The efficiency of a transformer at full load, 0.8 p.f. lag is 90%. Its efficiency at full load, 0.8 p.f. lead will be

Efficiency= output power/input power
efficiency = (v*i*cosφ)/((v*i*cosφ)+(x² Pc)+(Pi)) x=fractional part of full load

An over excited synchronous motor draws current at

Over excitation : leading current
Under excitation : lagging current
Normal excitation : current with unity PF (in phase current)

At time t= 0+ , with zero initial condition, which of the following acts as a short circuit?

Which type of back up protection is widely used for the protection of transmission lines?

It is difficult interrupt a capacitive current because

In the protection of transformers, harmonic restraint is used to guard against

Initial inrush of magnetizing currents have high component of even and odd harmonics.
2nd - 63%
3rd -26.8%
4th- 5.1%
5th- 4.1%
6th- 3.7
7th-2.4