The Implementation of Needle-Plane Electrode Configuration and Test Methods for Partial Discharge Inception Voltage Characteristic Measurement of Mineral Oil

Abstract

The investigation of the Partial Discharge Inception Voltage characteristic is performed by many researchers using the needle-plane electrode configuration and various test methods. This was conducted due to the capability of Partial Discharge Inception Voltage characteristic to represent or determine the condition of insulating liquid. This paper discusses the implementation of the needle-plane electrode configuration and two test methods to find out the characteristics of Partial Discharge in Partial Discharge Inception Voltage level of mineral oil. For this purposes, the mineral oil which used was Nynas Nitro 4000x with water content less than 10 ppm. In experiment, the test circuit was set up according to IEC 60270. The Ramp Method as the first test procedure was conducted in this experiment according to IEC 61294 with ramp rate of rise test voltage 1 kV/s until Partial Discharge Inception Voltage occurred. Meanwhile, a Combine Method as the second test procedure was used as comparative Partial Discharge Inception Voltage test technique. With this combine method, the test voltage was applied to the test object with rate of rise test voltage 1 kV/s until 70% of the Partial Discharge Inception Voltage value obtained from the ramp method. Then the test voltage was increased in steps with 1 kV/step with step duration of 1 minute until Partial Discharge Inception Voltage obtained with apparent charge ≥ 100 pC. The rest time between consecutive tests was 5 minutes. The needle tip radius that used as high voltage electrode were 10 µm and 20 µm, meanwhile brass plane electrode with diameter 75mm and 50mm was used as the grounded electrode. The gap distance between the needle electrodes toward ground electrode was fixed at 50 mm. The calculation of electric field stress of the needle-plane electrode configuration was done by using simulation of Finite Element Method (FEM). Based on the Partial Discharge Inception Voltage test result, the needle electrodes with tip radius 10 µm will produce electric field stress that higher than other needle tip, meanwhile the Partial Discharge Inception Voltage is lower which tested using both test method. By using the combine method, the Partial Discharge Inception Voltage value, charge quantity and the number of Partial Discharge will be lower than the ramp method. The results also showed that the Partial Discharge pulse currents using both test method was about 0.2 - 0.85 mA. The time duration of Partial Discharge pulse was in the range of 1.01 - 8.38 µs and the rise time were between 68 - 301 ns. It was found that the Partial Discharge Inception Voltage test result agree with the Weibull distribution