Polarity-reversed voltage pulse propagation analysis for power cable insulation diagnosis

Water tree degradation is major problem for power transmission cables. Water treeing is typical of the processes involved in the aging of XLPE cables, and it is known that it causes degradation of insulation performance. To avoid catastrophic failure, a method for localization of this water-treed section is required. We here propose a water-tree detection using polarity-reversed voltage pulses propagation. The polarity-reversed voltage pulses are impulse-like voltages having a exponential tail. We obtained a water tree degradation cable by accelerated deterioration aging test and measured the voltage pulse propagation. The measured pulse waveform involves a signal reflected by non-50 Ω. Although the reflection signal is a small peak, the experimental results qualitatively agreed with calculation results.