EGSA Electrical Systems Troubleshooting 3

Question 1

When a generator's output voltage collapses immediately upon applying load, the most likely cause is:

Accepted Answer

Shorted exciter diodes

Answer

Shorted exciter diodes prevent the field from building up sufficient current under load, causing voltage collapse when current demand increases.

Question 2

What is the purpose of performing a polarization index (PI) test on generator windings?

Accepted Answer

To assess insulation condition over time by comparing resistance at 1 and 10 minutes

Answer

The PI is the ratio of 10-minute to 1-minute insulation resistance readings; values above 2.0 generally indicate good insulation condition.

Question 3

A ground fault indicator lamp glows dimly on one phase of a 480V ungrounded delta system. This indicates:

Accepted Answer

A partial ground fault on that phase

Answer

In an ungrounded delta, a dim lamp indicates a partial or high-resistance ground fault; a solid ground fault would cause the lamp to go dark with the other two lamps glowing brighter.

Question 4

Which condition would cause a generator to produce voltage but fail to sustain it when a load is applied?

Accepted Answer

Weak residual magnetism in the rotor

Answer

Insufficient residual magnetism in the rotor prevents the field from self-exciting enough to sustain output voltage once load current is drawn.

Question 5

When troubleshooting a circuit with intermittent power loss, which technique is most effective for identifying a loose connection?

Accepted Answer

Thermal imaging under load

Answer

Thermal imaging detects heat generated by elevated resistance at loose connections under load, making intermittent faults visible before they cause failures.

(EGSA) Electrical Generating Systems Association Certified Practice Test

(EGSA) Electrical Generating Systems Association Certified Practice Test

EGSA Electrical Systems Troubleshooting 3