High Voltage DC Hipot Test for Power Cables Explained

What a DC Hipot Test Proves

A DC hipot (high-potential) test stresses cable insulation at a multiple of operating voltage to expose latent weaknesses—contamination, voids, partial-discharge sites—that an insulation resistance test alone cannot find. For medium-voltage XLPE cables in commissioning or maintenance, IEEE 400.1 still recognizes DC hipot as a go/no-go acceptance method, although VLF and tan-delta are increasingly preferred.

Test Voltage Selection

Standard practice for new XLPE cables is 3× rated phase-to-ground voltage for 15 minutes. For service-aged cables, reduce to 2× to avoid overstressing aged insulation. Always check the cable manufacturer datasheet for absolute maximum DC voltage.

Ramp Rate and Hold Time

• Ramp from 0 to test voltage at 1 kV/s or slower
• Hold for 15 minutes at full voltage
• Log leakage current at 1 min, 5 min, 10 min, 15 min
• Discharge ramp at the same rate, not by sudden grounding

Reading Leakage Current Trends

A healthy cable shows leakage current that rises during ramp-up, then settles to a stable plateau or slowly decreases due to dielectric absorption. Warning signs:

• Continuously rising current = thermal runaway, abort test
• Sudden current spikes = partial discharge or imminent breakdown
• Current that does not stabilize after 5 minutes = damp or contaminated insulation

Safety Procedures

DC hipot stores significant energy. Required precautions include grounded work mats, hot sticks for connection, two-person test crews, and a discharge stick that remains connected to the cable for at least 4× the test duration before any contact.

Reporting

EK hipot testers in the EK-9100 series automatically log voltage, leakage, temperature, and cable ID into a tamper-evident PDF report. Acceptance is documented when leakage stays below 5 µA/kV at the end of the hold period.