Study on the Surface Charge Accumulation of Post Insulators Considering Particle's Influences in DC GIL Hafiz Muhammad Azib Khan 1 , Li Botao 2 , Li Qingmin 1 , Wang Jian 1 , Wang Zhiyuan 1 1. Beijing Key Laboratory of High Voltage & EMC North China Electric Power University Beijing, China 2. State Grid Rizhao Power Supply Company, Rizhao, China Email: hafizm.azib@qq.com Abstract- Aiming at the problem of conducting particle pollution in DC-GIL, surface charge accumulation on the post-insulator is analyzed based on COMSOL and the platform for surface charge measurement. In this study, two surface charge accumulation models of the post-insulator with particle pollution were established taking the particle pollution, as well as the generating, recombination, migration and diffusion of the positive and negative ions in the gas into account. Based on these models, the impacts of attached particles on charge accumulation are explored by COMSOL, and the effectiveness and correctness of the simulations were verified through the experimental results from the platform. The results illustrate that, the accumulation of surface charge is affected by the conductive particles attached to the surface of the insulator greatly. In addition, the charge surge caused by the particles contact with the electrode is more remarkable, and the charge polarity at the ends of the particle which is located at the middle of the insulator is opposite to the polarity of the electrode. However, the charge polarity at the ends of the particle which is contact with the electrode is the same as the polarity of the electrode. The effect of micro-discharge on charge generation plays an important role on charge accumulation. I. INTRODUCTION Gas-insulated lines (GIL) has tended to be used widely, particularly in some special regions, due to its advantages in compactness, high reliability and large transmission capacity [1]. However, free metal particles may inevitably exist inside the enclosed structure in multiple ways. [2]. And the surface charge accumulation and conductive particle pollution are the main factors that cause flashover in DC GIL [3]. When they work together, their cause the most serious deterioration of the insulation strength. In several cases, the rigidity of the gases is found to be as low as 10% of the uncontaminated value [4]. Aiming at solving the surface charge and particle contamination problems in coaxial cylindrical electrode system, the predecessors have carried on extensive researches. Winter A analyses surface charge accumulation of insulator in the GIS with the microscopic mechanism of ions by using COMSOL and certain results are achieved [5]. Radwan analyses the interactions between particles and the surface charge accumulation theoretically [6]. And Chengrong Li explores the detection methods of surface flashover of the spacer with conductive particles attached on the surface [7]. A platform for surface charge measurement is established. And furthermore, taking the rates of generation, recombination, migration and diffusion of the positive and negative ions into account, a surface charge accumulation model of the post-insulator with particle pollutions using COMSOL Multiphysics is built correspondingly. Based on the simulations and experiments, the distribution of post insulator surface charge and the impacts of both attached particles on charge accumulation are explored. The results of simulations and experiments verify each other and indicate that attached particles plays an important role on charge accumulation. The regularities deduced in this paper are used to deepen the understanding of the surface flashover mechanism in DC GIL. II. EXPERIMENTAL SETUP In order to study the effect of metal particles on the surface charge accumulation of insulators, an appropriate experimental platform is built. The overall structure of the experimental platform is shown in Fig. 1. The whole electrode arrangement is installed in the cavity and measurements are performed under 0.1MPa SF6 at 20 ℃. In the experiment, the surface potential measurement is made by using a TREK-347 type electrostatic meter and a 555P-4 type capacitance probe which operate on the principle of field compensation. Experimental Cavity Trek 347 Trek 50/12 Power Amplifier Agilent 33500B signal generator Motor Controller Generates a voltage waveform magnified 5000 times Control probe Detect charge signal Generate Test Voltage Charge measurem ent and Motor control Fig. 1. The platform for surface charge measurement For eliminating the influence of the residual charge of particles and insulators on the experimental results, the surface of metal particles and insulators are wiped by ethanol before each experiment, and the experiment is carried out after ethanol completely volatiles (about 15min). Of course, repeated experiments are carried out to reduce the detection error.