43 / 2024-03-29 17:59:05

Study on Influencing Factors of Streamer Bifurcation Phenomenon in UHV GIS Disconnector Based on Phase-field Method

influencing factors,streamer bifurcation,GIS disconnector,phase-field method

In recent years, the phenomenon of breakdown to ground has been observed during the process of closing short busbar in the ultra-high voltage (UHV) gas insulated metal-enclosed switchgear (GIS) disconnector, as shown in Fig. 1, which poses a serious threat to the insulation and safe operation of UHV GIS equipment. However, there is insufficient attention on the breakdown characteristics during the operation of UHV GIS disconnector. Meanwhile, there is a lack of research on the influencing factors of streamer bifurcation phenomenon which is most likely cause of leading to the breakdown between the contactor and grounding shell of GIS disconnection. Therefore, to study the effects of different influencing factors about streamer bifurcation phenomenon, including metal particle, shielding cover of contact, voltage level, the streamer discharge model of GIS disconnector based on phase-field method is built. In this model, the principle of least action and streamer theory is integrated, which makes the development direction of phase transition equivalent to the development direction of discharge streamer. Firstly, the observation area of discharge of UHV GIS disconnector structure is focused on the area between the movable contact and static contact, as shown in Fig. 2(a), to build the discharge geometric model of UHV GIS disconnector, as shown in Fig. 2(b). Secondly, the simulation boundary conditions are set according to the UHV GIS experimental setup and circuit, including the potential of movable contact and static contact, gas medium of 0.45 MPa SF₆ between the movable contact and static contact. The initial state of the gas medium is insulation, meanwhile, initial state of surface defect and the metal particle is conductive. According to the phase field theory, the state change of order parameter of insulation medium, i.e., the phase state of SF₆ changing from insulation to conductive, is recognized as the development process of discharge streamer. Thirdly, the discharge path is obtained by analyzing variation of order parameter in the discharge process, as shown in Fig. 3. In the initial stage, a streamer with two development directions is formed at the movable contact position. The one is vertical to the static contact and the other is inclined development. After the streamer arrives at the static contact, the streamer has the probability to develop towards the ground shell, which possibly leads to a second breakdown. Finally, the discharge path of streamer is studied by controlling the variables including position of metal particle, the size of shielding cover of contact and the magnitude of voltage. The influence of metal particle on streamer is shown in Fig. 4. There is micro-discharge of metal particle in the direction near the streamer when streamer develops to the metal particle. Correspondingly, the increase of electric field strength makes it easier for the discharge streamer to break through the metal particle and streamer bifurcation phenomenon to form. Besides, the change of the size of shield cover and voltage level also affect the discharge path, and ultimately affect the formation of streamer bifurcation. This paper establishes the streamer discharge model of GIS disconnector based on phase-field method, by which the influencing factors on streamer bifurcation phenomenon and the development of the discharge path are analyzed. The study provides a theoretical basis of the ground breakdown fault causing by streamer bifurcation in GIS disconnector.