NETA Power Cable Test Methods 3

Question 1

What does a Dielectric Absorption Ratio (DAR) value greater than 1.25 typically indicate for cable insulation?

Accepted Answer

Good insulation condition

Answer

A DAR above 1.25 indicates the insulation resistance is still rising after 60 seconds, suggesting acceptably dry and clean insulation.

Question 2

When using the step voltage test on a cable, what does a sharp increase in leakage current at a specific voltage step indicate?

Accepted Answer

Incipient or existing insulation weakness at that stress level

Answer

A disproportionate current rise at a particular voltage step indicates the insulation has a defect that becomes active at that stress level.

Question 3

Which test is considered non-destructive and is recommended by IEEE 400 as a preferred diagnostic for medium-voltage XLPE cables?

Accepted Answer

VLF tan delta (dissipation factor)

Answer

VLF tan delta (loss angle) measurement is non-destructive and detects water treeing and insulation aging in XLPE cables without risk of damage.

Question 4

Before performing any hi-pot test on a cable, what must always be done first?

Accepted Answer

Perform an insulation resistance test and verify cable is de-energized and isolated

Answer

Verifying the cable is de-energized, isolated, and performing a preliminary IR test establishes baseline condition and ensures safety before applying high voltage.

Question 5

A shielded 15 kV XLPE cable fails a VLF withstand test. What is the most likely root cause indicated by this result?

Accepted Answer

Insulation has degraded below minimum withstand strength

Answer

Failure of a VLF withstand test means the insulation cannot sustain the required dielectric stress, indicating degradation such as water trees or thermal damage.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA Power Cable Test Methods 3