If a relay fails to operate inspite of a fault in its own zone of protection, it is said to

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

A 3 phase, 6 pole induction motor operates on 440 V, 50 Hz, supply. If the actual speed of the motor is 960 rpm the slip will be

Ns = 120f/P
Slip=(Ns-Nr)/Ns
Ns = 1000 and Nr = 960
from equation of slip, S = (1000-960)/1000
S = 0.04 or 4%

The positive and negative sequence impedance of a transmission line are

Due to skin effect

Skin Effect:
tendency of the current to crowd near the conductor surface.

Skin effect is proportional to frequency, conductor diameter and permiability.
Skin effect increases effective resistance of conductor.
In DC, no skin effect.

In carrier current protection, the purpose of the wave trap is for