GATE Electrical Engineering Practice Quiz

Question 1

A percentage differential protection scheme is used for a power transformer. Which quantity is primarily used as the restraining quantity in a biased differential relay?

Accepted Answer

Average of the magnitudes of currents entering and leaving the protected zone

Question 2

For a transmission line protected by a distance relay, the relay fundamentally measures which electrical quantity to estimate the fault location?

Accepted Answer

Apparent impedance seen from the relay location

Question 3

A distance relay on a long EHV line may underreach during a close-in fault with heavy DC offset and CT saturation. The most direct reason is that

Accepted Answer

the measured current is reduced, so the apparent impedance V/I becomes larger than actual

Question 4

For a single line-to-ground fault on a solidly grounded system, a ground distance relay commonly uses a residual compensation factor because

Accepted Answer

zero-sequence impedance differs from positive-sequence impedance, affecting the apparent impedance seen by the relay

Question 5

A directional overcurrent relay is required in a power system mainly when

Accepted Answer

fault current can flow in either direction due to multiple sources

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