The Statistical Characteristics Of Partial Discharges From Discharge Development To Insulation Breakdown In Discharge Fault Models Of Power Transformers

It is known that detecting partial discharge is an effective means for monitoring and evaluating the insulating condition in power transformers. The step-rising voltage and constant voltage accelerating aging methods were used to study the statistical characteristics of typical partial discharges from Discharge Development to Insulation Breakdown in Power Transformers. The partial discharges were measured by a pulse current sensor, an UHF sensor and an ultrasonic sensor. The tested results indicate that in the step-rising voltage accelerating aging testing, the maximal amplitudes of PD obtained from the gas, floating and pin-plane discharges in transformer oil increase with the applied voltage, detected by three kinds of sensors, and the numbers of PD detected by the UHF and ultrasonic sensors increase with the applied voltage. In the constant voltage accelerating aging testing, the numbers of PD obtained from the gas and pin-plane discharges, detected by the pulse current and UHF sensors, increase rapidly when the insulation was close to breakdown. In both testing, the numbers of PD obtained from all the models, detected by the UHF sensor, increase rapidly when the insulation was close to breakdown, and the maximal amplitudes of PD come to the maximum, and it was saturated when the insulation was close to breakdown. For all the models, the stronger of the discharge, the coherence between all detection methods is better. The phase of the gas discharges reached to 0~360 degree when the insulation was close to breakdown. The researches provided experimental data for predicting the insulating conditionof power transformer.