SOPD Protection Systems & Relay Operations

Question 1

What is the primary purpose of a protective relay in a power system?

Accepted Answer

To detect abnormal conditions and initiate disconnection of faulted equipment

Answer

To regulate voltage levels across the system

Answer

To control reactive power flow on transmission lines

Answer

To measure and record system frequency deviations

Question 2

Which relay type operates on the principle of measuring the ratio of voltage to current (impedance) to determine fault location?

Accepted Answer

Distance relay

Answer

Overcurrent relay

Answer

Differential relay

Answer

Directional relay

Question 3

In a zone-1 distance relay scheme, what percentage of the protected line's impedance is the reach typically set to?

Accepted Answer

80–85% to avoid overreaching into the remote bus

Answer

100% to ensure full line coverage

Answer

50% to provide an adequate time delay margin

Answer

120% to provide backup for the adjacent line

Question 4

What does a differential relay compare to determine whether a fault exists within its protected zone?

Accepted Answer

The current entering and leaving the protected equipment

Answer

The voltage at both ends of the protected equipment

Answer

The frequency difference between the two terminal buses

Answer

The impedance seen from each terminal of the line

Question 5

Which protection scheme uses a communication channel between two line terminals to achieve high-speed, simultaneous tripping for faults anywhere on the line?

Accepted Answer

Pilot protection (e.g., POTT or DCB)

Answer

Backup overcurrent protection

Answer

Step-distance protection with time delays

Answer

Thermal overload protection

Question 6

What is the function of a recloser in distribution and sub-transmission protection?

Accepted Answer

To automatically reclose a breaker after a fault to restore service for transient faults

Answer

To permanently isolate a faulted section from the system

Answer

To regulate voltage by switching capacitor banks in and out

Answer

To limit fault current by inserting impedance into the circuit

Question 7

A system operator is notified that a transformer differential relay has tripped. Before authorizing re-energization, the operator should FIRST:

Accepted Answer

Request a gas-in-oil or inspection test to determine whether an internal fault occurred

Answer

Re-energize immediately to restore load as quickly as possible

Answer

Reset the relay remotely and close the transformer breakers

Answer

Transfer all load to the backup transformer without investigation