Cable Testing and Diagnostics 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 Cable Testing and Diagnostics flashcards as text
During a time-domain reflectometry (TDR) test, a reflected pulse with the same polarity as the incident pulse indicates which type of fault?
Answer: Open-circuit fault
An open-circuit fault reflects the pulse with the same polarity because current cannot flow past the open, causing the voltage to double at that point.
What is the primary purpose of performing a partial discharge (PD) test on medium-voltage cables?
Answer: Detect internal voids and insulation defects before failure
Partial discharge testing identifies internal voids, contamination, and insulation degradation that can lead to eventual dielectric breakdown.
According to NETA standards, what minimum insulation resistance value (in MΩ) is generally considered acceptable for a 15 kV cable under NETA MTS acceptance criteria?
Answer: The standard references a comparison trend, not an absolute minimum
NETA MTS recommends evaluating insulation resistance trends and comparisons rather than relying on a single absolute minimum value, as cable IR varies with temperature, length, and age.
A tan delta (dissipation factor) test result that increases significantly with voltage indicates what cable condition?
Answer: Moisture ingress or aged/degraded insulation
A rising tan delta with increasing voltage (tip-up effect) indicates moisture ingress, water treeing, or degraded insulation that increases dielectric losses under stress.
When performing a very low frequency (VLF) hi-pot test on a cable, what frequency is typically used?
Answer: 0.1 Hz
VLF testing typically uses 0.1 Hz, which reduces the reactive current demand compared to 60 Hz, making it practical for testing long cable runs with portable equipment.
In a shield resistance test on a shielded cable, a high resistance reading compared to manufacturer specifications most likely indicates:
Answer: Corrosion, damage, or a break in the metallic shield
Elevated shield resistance indicates corrosion, physical damage, or continuity breaks in the metallic shield layer, which can compromise fault current return paths.
What does a negative reflected pulse polarity in a TDR trace indicate when compared to the incident pulse?
Answer: Short-circuit or low-impedance fault
A reflected pulse of opposite polarity to the incident pulse indicates a short-circuit or low-impedance anomaly, where the impedance drops below the characteristic cable impedance.