Physical Mechanism and Critical Starting Criterion of Wire Particle Firefly Movement under DC Electric Stress
Chang Yanan1, Geng Qiuyu2, Hu Zhiying2, Li Qingmin1
1. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China; 2. Beijing Key Lab of HV and EMC North China Electric Power University Beijing 102206 China
Abstract：In the DC gas-insulated switchgear and transmission lines (GIS/GIL), wire particles may exhibit a special firefly motion, namely, reverse motion without colliding with the ground electrode or suspended motion on the surface of the high-voltage electrode, which case is one of the principal factors affecting the insulation performance of the DC GIS/GIL. To clarify the physical mechanism of the firefly motion, a test platform was established to observe the firefly movement and measure the particle charge amount. The motion and charge characteristics of the wire particles at different voltage levels showed that, the polarity change of the particle charge due to the space charge near the wire particles was the key influential factor of the firefly movement, while the corona onset voltage of the wire particles on the electrode surface tended to be the critical voltage for the polarity change of the particle charge, as shown in Fig.1. The mechanism is applicable to the flake or spiral particles with low curvature radius, which generate similar space charge at the tip and change the charged polarity, leading to the firefly. Further, based on the photoionization model of the DC rod-plate gap corona, the corona onset voltage of the wire particles on the electrode surface was calculated, and the mathematical expression of the wire particle charge considering the corona voltage was fitted together with the measurement results. The charged wire particle motion model was thereby established considering the end concentration characteristics of the charge. Based on the proposed critical starting criterion of firefly, dynamic simulation of the linear particle flying motion was implemented as to obtain the onset electric field strength of firefly particles of different sizes in DC GIL. Then, the onset electric field strength of firefly particles with different sizes in DC GIL was calculated based on the charged wire particle motion model, as shown in Fig.2, and the validity of the calculation results is verified in real GIL. The obtained results indicated that, with the particle length increase, the particle radius decrease or the pressure decrease, the onset electric field strength of firefly particles decreased under positive and negative DC voltage. The onset field strength of a wire particle with 0.2mm diameter and 5 mm length in a 100kV GIL under 0.5MPa SF6 environment was 2.78MV/m for negative DC voltage and 4.93 MV/m for positive DC voltage. This study was based on the experiment in 110kV GIS, even though the particle motion characteristics at different voltage are numerically different from those at 110kV, the calculation method of particle motion characteristics are the same for different voltages. Therefore, the proposed research is suitable for DC GIL with different voltage levels, presents useful reference for DC GIL insulation design from the firefly particle suppression point of view.
常亚楠, 耿秋钰, 胡智莹, 李庆民. 直流电应力下线形微粒飞萤运动物理机制与临界起始判据[J]. 电工技术学报, 2023, 38(3): 648-658.
Chang Yanan, Geng Qiuyu, Hu Zhiying, Li Qingmin. Physical Mechanism and Critical Starting Criterion of Wire Particle Firefly Movement under DC Electric Stress. Transactions of China Electrotechnical Society, 2023, 38(3): 648-658.
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