AEP Troubleshooting & Diagnostics 2

Question 1

A three-phase motor runs but draws unbalanced current on all three phases. What is the most likely cause?

Accepted Answer

Unbalanced supply voltage

Answer

Unbalanced supply voltage causes unequal current draw across all three phases of a motor.

Question 2

Which instrument is best suited for locating a partial discharge site on a high-voltage cable?

Accepted Answer

Oscilloscope with PD detection

Answer

Partial discharge detection equipment using an oscilloscope captures high-frequency pulses that pinpoint defect locations.

Question 3

A distribution transformer hums louder than normal but output voltage is within spec. What should you suspect first?

Accepted Answer

Loose core laminations

Answer

Loose core laminations vibrate at twice the power frequency, producing excessive humming noise.

Question 4

During a power factor test on a transformer, a high dissipation factor reading indicates:

Accepted Answer

Moisture or contamination in insulation

Answer

A high dissipation factor (tan delta) indicates moisture, contamination, or deterioration in transformer insulation.

Question 5

A relay fails to trip during a fault simulation. After checking the relay element, what should you test next?

Accepted Answer

Trip coil continuity and DC control voltage

Answer

The trip coil and control voltage supply are the most common causes of a relay failing to trip after the relay element itself is verified.

(AEP) American Electric Power Practice Test