Q: Why is DC Hipot now strictly forbidden by standards like IEEE 400.1 for XLPE cables?
A: Because XLPE is a solid polymer. Under high DC electric fields, it suffers from a destructive phenomenon called Space Charge Accumulation.
The Damage Mechanism:
• Electron Trapping: DC voltage drives electrons/ions into insulation, trapping them at polymer interfaces.
• Trapped Charge: Static charge remains trapped inside the insulation for days or weeks after the test.
• AC Power Return: Flipped polarity 50/60 times/sec causes the AC field to double-up against trapped charge.
• Result: Local field skyrockets (E_total = E_AC + E_space), causing instant treeing and rapid breakdown.
IEEE Standard View: IEEE 400.1 states that DC testing of XLPE can cause permanent insulation damage. It doesn't find real defects; it just damages healthy parts.
