NETA Cable Testing and Diagnostics 1

Question 1

A DC hi-pot test on a shielded power cable measures:

Accepted Answer

The cable's insulation integrity by applying DC overvoltage and monitoring leakage current

Answer

The AC dielectric strength under operating conditions

Answer

The cable's impedance and capacitance per unit length

Answer

The continuity of the cable shield/sheath

Question 2

The VLF (Very Low Frequency) test for medium-voltage cables uses a test frequency of approximately:

Accepted Answer

0.1 Hz, which reduces the charging current requirement by a factor of 600 compared to 60 Hz testing

Answer

60 Hz (same as power frequency)

Answer

1000 Hz for faster testing

Answer

DC with a ripple component at low frequency

Question 3

Time Domain Reflectometry (TDR) is used on power cables to:

Accepted Answer

Locate the position of faults, splices, and discontinuities by measuring the travel time of reflected pulses

Answer

Measure the insulation resistance along the cable length

Answer

Test the cable's high-frequency attenuation characteristics

Answer

Measure the capacitance of the cable for energy calculation

Question 4

The dielectric loss tangent (tan delta) test on cables measures:

Accepted Answer

The ratio of resistive (loss) current to capacitive current, indicating insulation quality and aging

Answer

The electrical breakdown strength of the insulation at high voltage

Answer

The capacitance of the cable per unit length

Answer

The corona inception voltage of the cable insulation

Question 5

Cable jacket testing (sheath integrity testing) using DC current verifies:

Accepted Answer

That the outer jacket/sheath has no breaches allowing moisture to reach the metallic shield

Answer

The integrity of the phase conductor insulation

Answer

The ampacity of the cable under burial conditions

Answer

The bond between jacket and insulation in the cable construction

Question 6

Partial discharge (PD) measurement on a medium-voltage cable system identifies:

Accepted Answer

Localized defects in the insulation or accessories (splices, terminations) where PD activity is concentrated

Answer

The total insulation resistance of the cable run

Answer

The cable's rated voltage class and insulation level

Answer

Short-circuit current capacity of the cable