Electrical Equipment & Maintenance Flashcards
7 cards from real EETC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Electrical Equipment & Maintenance flashcards as text
What is the primary purpose of a megohmmeter (megger) in electrical maintenance?
Answer: Test insulation resistance of cables and motors
A megohmmeter applies high DC voltage to measure insulation resistance, detecting degraded or damaged insulation before failures occur.
When performing a polarization index (PI) test on a motor winding, a PI ratio below 1.0 indicates:
Answer: Severely contaminated or damaged insulation
A PI ratio below 1.0 means insulation resistance decreased during the test, indicating moisture saturation, contamination, or serious deterioration.
Which type of capacitor failure mode causes an electrolytic capacitor to vent or bulge?
Answer: Excessive ripple current causing internal heating
Excessive ripple current heats the electrolyte, generating gas pressure that bulges or ruptures the vent on an electrolytic capacitor.
In a three-phase induction motor, what condition is indicated by high vibration at twice line frequency (120 Hz in a 60 Hz system)?
Answer: Loose stator laminations or electromagnetic looseness
Vibration at 2× line frequency (120 Hz) is a classic signature of electromagnetic looseness, often caused by loose stator core laminations.
A transformer's dissolved gas analysis (DGA) shows high levels of acetylene (C₂H₂). What fault does this indicate?
Answer: High-energy arcing or electrical discharge
Acetylene is produced only at very high temperatures (above 700°C), making it a definitive marker of high-energy arcing inside the transformer.
What is the correct procedure when re-energizing a motor that has been stored for an extended period?
Answer: Perform a megger test and dry out windings if resistance is low before energizing
Long storage allows moisture to accumulate in windings; a megger test verifies insulation integrity and drying out is required if resistance is below minimum acceptable values.
Which maintenance technique uses ultrasonic detection to identify problems in electrical equipment?
Answer: Detecting partial discharge, corona, and arcing in switchgear
Ultrasonic detectors pick up high-frequency sound emissions from corona, partial discharge, and arcing that are inaudible to the human ear.