Life estimation of water tree deteriorated XLPE cables by VLF (very low frequency) voltage withstand test

The authors investigated a new life estimation method for service-aged, water tree deteriorated 22-77 kV XLPE cables by voltage withstand test. At first, they selected more suitable waveform for testing voltage from damped oscillating wave (OSW) and very low frequency wave (VLF) voltage as the instead of AC and DC. It was found that VLF voltage has high ability to detect of water tree, while was less harmful for water tree deteriorated cables. Breakdown tests under AC and VLF were carried out, using model cables and service aged XLPE cables. Based on the breakdown tests, they calculated optimal test voltage for remaining life estimation. Recently, they had onsite testing and confirmed the effectiveness of VLF testing.