NETA Protective Relay Applications 3

Question 1

When testing a directional overcurrent relay (67), which reference quantity is typically used for directional discrimination?

Accepted Answer

Polarizing voltage or current

Answer

Directional relays use a polarizing quantity (voltage or current) as a reference to determine whether the fault is in the forward or reverse direction.

Question 2

A generator protection relay setting for loss-of-field (40) is based on the measurement of:

Accepted Answer

Reactive power absorption (leading current)

Answer

Loss of field causes the generator to absorb reactive power (operate in an under-excited leading power factor condition), which the impedance-based relay detects.

Question 3

What is 'CT saturation' and how does it affect differential relay performance?

Accepted Answer

CT core saturates under high current, producing distorted secondary current that can cause false differential trips

Answer

CT saturation during external faults produces distorted secondary currents that appear as differential current, potentially causing false relay operation.

Question 4

In transformer differential protection, what is the purpose of the harmonic restraint feature?

Accepted Answer

To block tripping during magnetizing inrush current which contains significant 2nd harmonic

Answer

Inrush current during transformer energization contains high 2nd harmonic content, and harmonic restraint uses this to distinguish inrush from internal fault current.

Question 5

Which ANSI device number is assigned to a breaker failure relay?

Accepted Answer

50BF

Answer

ANSI device number 50BF designates the breaker failure protection function, which initiates backup tripping if the primary breaker fails to open.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA Protective Relay Applications 3