When a cable is taken out of service for maintenance or repairs, it should undergo pressure testing before being placed back in service. This applies to both existing cables and new installations.

Reasons for Pressure Testing

• Fault Detection: Testing helps identify existing fault spots critical to the cable’s safe operation, breaking them down without further affecting the quality or lifespan of unaffected sections.
• Condition Evaluation: Testing provides insights into the condition of cable joints and accessories, assessing their quality and overall integrity.
• Failure Prevention: Proper testing minimizes the risk of failures during network operation, preventing potential damage to associated cables and components. If a cable fails under load, fault currents can travel through it, potentially damaging other sections.

DC Pressure Testing

Historically, high-voltage cables were tested with DC pressure testing, which was effective for PILC (Paper Insulated Lead Covered) cables. However, this method proved ineffective and potentially damaging for XLPE (Cross-Linked Polyethylene) cables.

Why DC Testing Is Not Suitable for XLPE Cables

DC pressure testing can cause damage to XLPE cables. Under prolonged high DC voltages, fault spots may break down, but this process can also damage undamaged cable sections, accelerating their aging. Additionally, long exposure to high DC voltage generates residual space charges that dissipate very slowly. Once the cable is re-energized, residual charges interact with the AC electrical fields, leading to an uncontrolled breakdown during operation.