多场协同诱导三支柱绝缘子缺陷级联放电脆裂的竞争机制OA

Gas-insulated metal-enclosed transmission lines(GIL)have been widely used in the new power system in recent years.However,the key insulating component,the tri-post insulator,is prone to discharge brittleness faults due to its complex structure and interface defects generated during production,transportation and operation.It is urgent to carry out relevant research to clarify the brittleness mechanism.Based on the 550 kV true insulator scale model,this paper constructed a tri-post insulator electro-thermal-mechanical synergistic discharge brittle fracture test platform.The platform mainly includes a high-voltage power supply,a closed cavity,a pressurization device,an ultrasonic partial discharge device,a high-speed camera,and an oil bath heating device.The dynamic evolution process of the crack was observed.The discharge embrittlement laws under the influence of different voltage types,defect sizes,mechanical stress magnitudes and other factors were analyzed.The mechanism of cascade discharge embrittlement was revealed by experimental results and simulation analysis.By combining electric potential energy,elastic potential energy and thermal energy,a model of crack driving energy release rate was established and the fracture criterion was proposed,clarifying the mechanism of different energy competition with voltage and stress changes. The experimental results and phenomena show that the crack development is divided into crack propagation,breakdown flashover and brittle fracture stages.The weak discharge signal becomes stronger from weak and gradually develops to breakdown flashover.Due to the coupling effect of electric field distortion and stress concentration at the epoxy bonding interface,the breakdown voltage is reduced by 20.9%and 9.5%respectively compared with the outriggers.As the depth of the crack increases,the probability of brittle cracking rises to up to 75%at most.The longer the crack length and the narrower the thickness,the more likely it is to break through and become brittle.Negative polarity direct current is more prone to cracking than positive polarity.Under the action of alternating current,the breakdown voltage drops by 25.13%,and the drop is more obvious after superimposing the impulse voltage.The external stress causes severe impact.The difference between the breakdown voltage and the brittle fracture voltage is relatively small,and the decrease is significant after 1.5 kN.Stress exceeding 2 kN can shorten the brittle fracture time by approximately 43%.Simulation analysis reveals that the coupling effect of high electric field and stress concentration at the crack tip leads to damage and propagation of the crack tip and provides a channel for the formation of flow injection. Based on the criterion of the critical energy release rate of the electric-thermal-force coupling,it is concluded that at 2 kN,the critical extended calculated voltage is 63 kV,which is close to the experimental 67 kV.The average error under different stresses is 6.9%,verifying the validity of the criterion.The crack propagation voltage and experimental error are 6.9%.Under low load,the competition among elastic potential energy,electric potential energy and thermal energy is fierce,and the dominance alternates with the increase of voltage.However,under high stress,mechanical potential energy dominates,always accounting for more than 60%.Four-parameter Logistic fitting is adopted for this competition model.By changing the corresponding parameters,the specific gravity variation laws can be obtained for different stress magnitudes.