EGSA Electrical Systems Troubleshooting 4

Question 1

Excessive third-harmonic distortion in a generator's output is most commonly caused by:

Accepted Answer

Non-linear loads such as UPS systems and VFDs

Answer

Non-linear loads draw current in pulses rather than sinusoidal waves, generating third and other odd harmonics that distort the generator output waveform.

Question 2

When load testing a generator, what parameter confirms the generator is operating within its rated kVA capacity?

Accepted Answer

Both kilowatts and kVAR readings within nameplate rating

Answer

kVA capacity is determined by both the real power (kW) and reactive power (kVAR) components, and both must be within nameplate limits to confirm proper operation.

Question 3

A parallel-connected generator is importing reactive power (absorbing VArs) instead of exporting. The likely cause is:

Accepted Answer

Under-excitation of the generator field

Answer

Under-excitation causes the generator to operate in a leading power factor mode, absorbing reactive power from the bus rather than supplying it.

Question 4

What is the most appropriate test to verify continuity of a generator's rotor winding without disassembly?

Accepted Answer

Slip ring resistance measurement with an ohmmeter

Answer

Measuring resistance across the slip rings with an ohmmeter checks rotor winding continuity and compares the reading against the manufacturer's specification.

Question 5

Which fault condition causes unequal voltage readings across each phase of a three-phase generator but normal frequency?

Accepted Answer

Partial short in one phase stator winding

Answer

A partial short in one phase stator winding reduces the turns ratio and output impedance of that phase, lowering its voltage while the other phases remain normal.

(EGSA) Electrical Generating Systems Association Certified Practice Test

(EGSA) Electrical Generating Systems Association Certified Practice Test

EGSA Electrical Systems Troubleshooting 4