Numerical Analysis of Partial Discharge Behaviour Under DC Stress With Voltage Disturbance at Different Void Sizes

Partial discharge (PD) is commonly related to electrical insulator degradation. It occurs in a high electric field environment, especially in high-voltage systems. It can lead to the electrical breakdown of insulators. Knowledge of the characteristics of PD allows for testing and monitoring of insulation properties in power system equipment. PD can be observed in both AC and DC power. However, research on AC-PD is much more mature than DC-PD due to the established pattern of AC’s changing magnitude and polarity characteristics. This work uses finite element analysis to study PD activity under DC stress with voltage disturbance at different void sizes, with AC harmonic as the focused disturbance. The characteristics are evaluated based on the electric potential distribution, electric field distribution, electrical charges, and repetition rate. As the void radius increases from 1 mm to 4 mm, the inception voltage decreases by approximately 65%, while the PD repetition rate increases by 58%. In addition, a comparison between DC-PD and AC harmonic disturbance and AC-PD is performed to analyze their differences. The simulation result shows that the repetition rate for DC-PD with AC harmonics is approximately 75% lower than that of AC-PD, indicating fewer PD events in the case of DC-PD with AC harmonics. The conducted simulation provides valuable insights and guidance for the formation of DC-PD testing, and consequently, a validated method can be approved to monitor insulating material condition under DC power. ABSTRAK: Penyahcasan separa (partial discharge, PD) merupakan fenomena biasa yang berkait rapat dengan degradasi penebat elektrik. Ia berlaku dalam persekitaran medan elektrik tinggi, khususnya dalam sistem voltan tinggi, dan boleh menyebabkan kerosakan elektrik pada penebat. Pengetahuan mengenai ciri-ciri PD membolehkan ujian dan pemantauan sifat penebat dalam peralatan sistem kuasa dijalankan. PD boleh diperhatikan dalam kedua-dua kuasa arus ulang-alik (AC) dan arus terus (DC). Namun, kajian mengenai PD dalam AC adalah lebih matang berbanding dalam DC disebabkan oleh corak perubahan magnitud dan polariti AC yang telah mapan. Kajian ini meneliti aktiviti PD di bawah tekanan DC dengan gangguan voltan pada saiz kekosongan yang berbeza menggunakan analisis elemen terhingga, dengan gangguan harmonik AC sebagai tumpuan utama. Ciri-ciri yang dinilai termasuk taburan potensi elektrik, taburan medan elektrik, cas elektrik, dan kadar pengulangan. Apabila jejari kekosongan meningkat dari 1 mm kepada 4 mm, voltan permulaan menurun sebanyak kira-kira 65%, manakala kadar pengulangan PD meningkat sebanyak 58%. Selain itu, perbandingan antara PD-DC dengan gangguan harmonik AC dan PD-AC turut dilakukan bagi menganalisis perbezaannya. Hasil simulasi menunjukkan bahawa kadar pengulangan bagi PD-DC dengan gangguan harmonik AC adalah kira-kira 75% lebih rendah berbanding PD-AC, menandakan bilangan kejadian PD yang lebih sedikit dalam kes PD-DC dengan gangguan harmonik. Simulasi yang dijalankan ini memberikan pandangan yang bernilai dan panduan berguna bagi pembentukan ujian PD-DC, dan seterusnya, kaedah yang disahkan boleh diluluskan untuk memantau keadaan bahan penebat di bawah kuasa DC.