| Surge Arrestor is a common overvoltage protection appliance in power systems.Metal-oxide Surge Arrestor(MOA)has been more and more widely used because of its advantages of high flow capacity,short response time,excellent nonlinear characteristics,simple manufacturing structure and strong anti-pollution ability.However,during the long-term operation,the MOA resistor will cause deterioration defects due to dampness overheating,resulting from a decrease in the insulation performance of the resistor.If the defect is not discovered and handled in time,it will cause the thermal breakdown of the arrester,resulting in serious Power failure accident.Therefore,it is an important and urgent work to find the defects and the causes of the deterioration of the resistance sheet as early as possible,and accurately judge the aging degree of the resistance sheet.This thesis firstly conducted a series of accelerated degradation tests for zinc-oxide resistors.The test used a programmable box muffle furnace to heat and degrade the resistor at different temperatures.The test also used the solution to humidify the resistor to varying degrees to make it damp.It was found that the insulation resistance value of the resistance sheet will drop to a certain extent under high temperature or moisture,and as the degree of deterioration deepens,the decrease in insulation resistance value is higher.On the basis of the preliminary test,3D modeling and finite element simulation calculations are carried out for MOA.Simulation has calculated the effect of single resistors with different degrees of deterioration on the electric field distribution and current density distribution of MOA in actual operation.Observe the heat generation of MOA from the resistance sheet inside the model and the external composite jacket.It was found that the deterioration of the resistance sheet caused the current density to increase due to the decrease in the insulation resistance value.In the worst case,the temperature increased by about 1 ? compared to the normal MOA.In order to verify the simulation results,this paper builds AC and DC test platforms to compare and correct the test and simulation results.The test measured the leakage current change level and heat generation caused by the deterioration of the MOA resistor in the AC system.At the same time,the results of the DC test platform were used for comparison.The test results prove that the simulation results are more consistent with the actual operation.In order to study the development mechanism of thermal runaway caused by the deterioration of a small number of resistors.In this paper,the MOA was re-simulated after modifying the environmental parameters.In the simulation,multiple adjacent degraded resistors were introduced to analyze the electric field,current density,and temperature distribution again.Through the results,it is found that the resistor sheet that has deteriorated will cause the voltage borne by the adjacent normal resistor sheet to increase,and the current density to increase,thereby causing the temperature of the adjacent resistor sheet to increase to a certain extent.This phenomenon is particularly evident on the grounded side.Therefore,it is believed that under long-term high-temperature operating conditions,the resistors will accelerate to deteriorate.At the same time,the resistors that have already deteriorated will continue to cause changes in the operating environment of their adjacent resistors,resulting in a deeper degree of deterioration.The non-degraded resistors have a deteriorating chain reaction.If failures are not found and eliminated in time,it will eventually lead to thermal runaway of the MOA and cause serious power outages.The research work in this paper lays a certain foundation for further experiments and simulations,and provides theoretical and data support for improving the design,installation,operation and maintenance processes of MOA,and is of great significance for improving the safety and reliability of the power grid. |
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