EGSA Electrical Systems Troubleshooting 5

Question 1

During a voltage dip test, a generator's voltage recovers but takes longer than the manufacturer specifies. What is the most likely cause?

Accepted Answer

Sluggish AVR response due to incorrect gain setting

Answer

The AVR gain setting controls response speed; too-low gain causes slow voltage recovery after transient load application, exceeding the specified recovery time.

Question 2

What is the significance of a high kW but low kVA reading on a generator under load?

Accepted Answer

The power factor is near unity, indicating mostly resistive load

Answer

When kW approaches kVA, the power factor is near 1.0 (purely resistive load), meaning little reactive power is being consumed, which is an efficient operating condition.

Question 3

A generator produces correct voltage at no-load but the output collapses when connected to a motor starting load. What should be evaluated?

Accepted Answer

Generator's transient reactance and short-circuit capability

Answer

Motor starting draws large inrush current; if the generator's transient reactance is too high or it is undersized, its terminal voltage will sag excessively or collapse during motor acceleration.

Question 4

Neutral-to-ground voltage above 2V in a solidly grounded 120/208V system typically indicates:

Accepted Answer

Excessive neutral current due to unbalanced or non-linear loads

Answer

High neutral current from load imbalance or harmonic-generating equipment causes a measurable voltage drop along the neutral conductor, raising neutral-to-ground voltage above acceptable levels.

Question 5

When a generator fails to build voltage after a field flash attempt, the next step is to:

Accepted Answer

Test the rotating rectifier diodes for open or short circuit

Answer

If field flashing doesn't build voltage, the rotating rectifier diodes that supply DC to the main rotor field should be tested, as a failed diode prevents field current flow.

(EGSA) Electrical Generating Systems Association Certified Practice Test

(EGSA) Electrical Generating Systems Association Certified Practice Test

EGSA Electrical Systems Troubleshooting 5