SOPD Protection Systems & Relay Operations 3

Question 1

Which of the following relay characteristics is best suited for protecting a high-voltage transmission line where load encroachment may be a concern?

Accepted Answer

Quadrilateral characteristic

Answer

The quadrilateral characteristic allows independent adjustment of resistance and reactance boundaries, enabling the operator to shape the trip zone to avoid load encroachment while still covering high-resistance faults.

Question 2

What is the purpose of a 'zone 3' setting in a step-distance protection scheme?

Accepted Answer

To provide remote backup protection for adjacent lines beyond zone 2

Answer

Zone 3 is set to reach beyond the adjacent line to provide remote backup protection if the relays or breakers at the far terminal fail to clear a fault; it operates with the longest time delay.

Question 3

A 'Permissive Overreaching Transfer Trip' (POTT) pilot scheme sends a permissive signal when:

Accepted Answer

The local relay detects a fault within its overreaching zone (zone 2 or beyond)

Answer

In POTT, both terminals must detect the fault in their overreaching zones and exchange permissive signals; receipt of both signals enables high-speed tripping, ensuring the fault is internal to the line.

Question 4

When a system operator is required to take protective relay equipment out of service for maintenance, which of the following actions is typically required?

Accepted Answer

Obtain approval and implement compensating measures per the applicable protection maintenance standard

Answer

PRC-005 and applicable reliability standards require approval and compensating protection measures (backup relay verification, load reduction, etc.) when primary protection is taken out of service.

Question 5

What phenomenon can cause a distance relay to 'underreach' (fail to detect a fault within its set zone)?

Accepted Answer

High fault resistance in the fault path

Answer

High fault resistance adds resistance to the measured impedance, causing the apparent impedance to appear outside the relay's set zone, resulting in underreach and failure to trip.

(SOPD) System Operator/Power Dispatching Practice Test

(SOPD) System Operator/Power Dispatching Practice Test

SOPD Protection Systems & Relay Operations 3