Distribution of discharge magnitude under local breakdown condition in void

Insulation deterioration tests were carried out using an internal-discharge-pulse measurement system with the aim of predicting the breakdown of electrical equipment. The system analyzes the distribution of discharge magnitude relative to each phase angle of the applied voltage (AC 50 Hz). The distribution of the discharge magnitude in the sample (consisting of three polyethylene layers) was measured, which was intentionally broken down in part of a void. It was found that, when the breakdown of one side of the sample took place, the number of discharge pulses of large magnitude decreased and the number of discharge pulses of small magnitude increased. When the change in the distribution of the discharge magnitude was observed the breakdown pit in one side of the sample was confirmed. It is concluded that the change in the distribution of the discharge magnitude could be used as a tool for the diagnosis of the deterioration of insulation