Direct-detect Type Residual Charge Method with Short-term Voltage Up-down for Water Tree Deterioration Diagnosis in XLPE Cable

Water tree deterioration diagnosis for 10 kV XLPE cable based on Residual Charge Method

“…The amount of residual charge was calculated using the following equation: Q=QI-QzxQZ/Q3 where Q is the amount of residual charge; Q], Qz and Q3 are the amounts of charge calculated by integrating the current flowing in the circuit during the first one-third, second one-third and third one-third of the total application time of pulse voltage. It's reported that residual charge signal will be released in several seconds or scores of seconds [2], therefore, QI contains the amounts of charges induced by noise, pulse voltage and detrapped ones while Qz and Q3 only contain the amount of charges induced by noise and pulse voltage. Then, Q ZxQZ /Q3was thought to be approximately equal to the amount of charges induced by noise and pulse voltage in QI and was subtracted from Q], thus the amount of residual charge Q was obtained.…”

“…Insulation impedance method and DC leakage current method, proposed for the diagnosis of bridged water tree in XLPE cable with the voltage class less than 6 kV, is ineffective for the detection of non-bridged water tree [2]. Residual Charge Method is well-known for its effectiveness in the diagnosis of non-bridged water tree.…”

“…In this method, DC voltage is applied to water tree degraded cable to inject charges. After grounding, the amount of residual charge serving as an indicator of water tree degradation degree is detected when AC voltage is being applied [2]. Using [4].…”