Mission Brief

The Buried Kilometre You Can't See

A new 22 kV XLPE feeder has been pulled between two switchrooms and jointed in a pit halfway. Before it is energized it has to be proven — but it is buried, so every judgement is made from its terminals. Is the insulation dry? Will it hold three times its working voltage? Was the jacket nicked when it was dragged in? And is it really the length the record says, with nothing wrong in between?

• Measure insulation resistance and the polarization index (PI)
• Apply the VLF withstand at the commissioning voltage (≈ 3·U₀)
• Prove the oversheath with a DC jacket test
• Verify the cable length with TDR
• Discharge the cable safely and issue the record