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
When replacing a failed contactor, which specification is MOST critical to match for motor protection?
Answer: Continuous current rating and interrupting capacity
The continuous current rating must handle full-load amperes and the interrupting capacity must safely break fault currents without damage.
In a variable frequency drive (VFD), what is the function of the DC bus capacitor bank?
Answer: Filter and smooth the rectified DC voltage for the inverter section
DC bus capacitors smooth the pulsating rectified voltage into steady DC, reducing ripple and providing energy storage for the inverter section.
What does a high dielectric absorption ratio (DAR) value indicate about transformer oil?
Answer: Oil is in good condition with high dielectric strength
A high DAR (ratio of 60-second to 30-second insulation resistance) indicates clean, dry insulating oil with good dielectric properties.
A power factor correction capacitor bank is found to have one failed (open) capacitor unit. What is the immediate effect on the bank?
Answer: Remaining units in that phase see increased voltage stress
With one capacitor open in a series-parallel bank, remaining parallel capacitors in that section carry the full voltage, increasing stress and risk of cascading failure.
During preventive maintenance on switchgear, vacuum bottle integrity is verified by:
Answer: Applying a high-potential (hi-pot) test across open contacts
A high-potential test across the open vacuum interrupter verifies that the vacuum is intact and can withstand the required dielectric strength.
What is the purpose of a load bank test on a standby generator?
Answer: Exercise the generator at rated load to prevent wet-stacking and verify performance
Load bank testing runs the generator at rated capacity, preventing wet-stacking in diesel engines and confirming the unit can carry its full rated load.
When using thermal imaging (infrared) on electrical panels, a three-phase load imbalance typically appears as:
Answer: One phase significantly hotter than the other two
An overloaded or unbalanced phase shows elevated temperature compared to the other two balanced phases due to higher I²R losses.