NETA Cable Testing and Diagnostics 4

Question 1

During a time-domain reflectometry (TDR) test, a reflected pulse with the same polarity as the incident pulse indicates which type of fault?

Accepted Answer

Open-circuit fault

Answer

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.

Question 2

What is the primary purpose of performing a partial discharge (PD) test on medium-voltage cables?

Accepted Answer

Detect internal voids and insulation defects before failure

Answer

Partial discharge testing identifies internal voids, contamination, and insulation degradation that can lead to eventual dielectric breakdown.

Question 3

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?

Accepted Answer

The standard references a comparison trend, not an absolute minimum

Answer

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.

Question 4

A tan delta (dissipation factor) test result that increases significantly with voltage indicates what cable condition?

Accepted Answer

Moisture ingress or aged/degraded insulation

Answer

A rising tan delta with increasing voltage (tip-up effect) indicates moisture ingress, water treeing, or degraded insulation that increases dielectric losses under stress.

Question 5

When performing a very low frequency (VLF) hi-pot test on a cable, what frequency is typically used?

Accepted Answer

0.1 Hz

Answer

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.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA Cable Testing and Diagnostics 4