Power Systems Analysis & Troubleshooting Flashcards
7 cards from real NETA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Power Systems Analysis & Troubleshooting flashcards as text
A symmetrical three-phase fault calculation requires knowledge of the system's:
Answer: Positive-sequence impedance only
A balanced three-phase fault involves only positive-sequence network, so only positive-sequence impedance is needed.
When testing a motor for insulation condition using a Polarization Index (PI) test, a PI value below 2.0 for a Class B motor indicates:
Answer: Questionable insulation requiring further evaluation
A PI below 2.0 for most rotating machinery indicates questionable insulation condition that warrants further investigation before energizing.
In a power system short circuit study, the X/R ratio is important because it determines:
Answer: The DC offset component of fault current and equipment duty
The X/R ratio governs the DC offset decay rate, which affects peak asymmetrical fault current and equipment interrupting duty.
A grounded wye-delta transformer connection is commonly used as a grounding transformer primarily to:
Answer: Provide a zero-sequence current path on an otherwise ungrounded system
A grounded wye-delta (or zigzag) grounding transformer provides a zero-sequence current path, enabling ground fault protection on ungrounded systems.
During a frequency sweep (sweep frequency response analysis) test on a transformer, a change in the high-frequency signature compared to the baseline most likely indicates:
Answer: Winding deformation or displacement
High-frequency signature changes in SFRA testing indicate mechanical winding deformation or displacement, often from through-fault forces.
The primary purpose of a transfer trip scheme in transmission line protection is to:
Answer: Communicate a trip command to a remote breaker for high-speed clearing
Transfer trip sends a direct trip signal via communications channel to the remote terminal breaker to achieve simultaneous high-speed fault clearing.
When measuring zero-sequence impedance of a transformer, the test is performed by:
Answer: Connecting all three LV phases together and driving current with the neutral
Zero-sequence impedance is measured by connecting all three phase terminals together and between that junction and the neutral, measuring voltage and current.