The possibility of using a needle plane electrode for partial discharge inception voltage measurement

Abstract

The propose of this paper is to elucidate the Partial Discharge Inception Voltage(PDIV) measurement for liquid insulation by using a needle - plane electrode. This paper presents the experimental investigation of PDIV and PD characteristics of the mineral oil tested by different electrode configuration. The experiment was performed by using a needle - plane electrode with a tungsten needle tip radius of 10 μm and a brass plane electrode with a diameter of 75 mm compared with measuring by the 10 μm tip radius needle - a steel sphere electrode with a diameter of 12.7 mm. This sphere electrode diameter is in the range of the standard sphere electrode for the PDIV test recommended by IEC 61294. Nynas nytro 4000x, with water content not more than 10 ppm was used for this research. The lengths of the needles were specified as 25 ± 0.5 mm and 45± 0.5 mm respectively. Two gap distance of 25 mm and 50 mm of the electrode system were fixed for investigation. To calculate the pattern of electric field of these electrode systems, the Finite Element Program was utilized. Then, the test experiment was carried out. The test circuit was conducted in accordance with IEC 60270. The test process was divided into two test methods. The former test method was carried out in conformity with IEC 61294. The latter test method was a ramp - step combination test method. Details of both test methods are described in this paper. The maximum electric field stress, the PDIV mean value and the phase - resolved PD characteristics of both electrode systems are analyzed. The test results revealed that the needle-plane electrode system can detect the PDIV value at the lower test voltage and gives the higher QIEC value compared with testing by the needle - sphere electrode system. The PDIV test results agree with the maximum electric field stress of the electrode systems. Moreover, the ramp - step combination test method gave the lower PDIV and PD amplitude recorded for 1 minute than PDIV testing comply with the IEC standard.