| Résumé | The on-site diagnostics of medium-voltage underground cross-linked polyethylene cables were investigated. The measurement instrumentation, equipped with a portable generator and power amplifier for obtaining clean 60-Hz power and dc voltage up to -10 kV, can be fitted into a mid-size van. The connections to remote terminals, as far as 100 m from the van, are made by coaxial cable. The HF components of the depolarization current can have amplitudes of the order of amperes and a very short decay time, of the order of microseconds. The low-frequency components are of the order of picoamperes but of a much longer duration, of the order of tens of seconds. The increase of depolarization current magnitude with the poling time is an indication of the presence of slow dipolar polarization processes such as those involving hydrated ionic contaminants often found in water trees. The dependence of the depolarization current on the dc charging time indicated a significant population of water trees in the tested cables. |
|---|
