| Zinc oxide lightning arrester on the roof is an important overvoltage protection device for multiple units.During on-site operation,it can suffer from various types of overvoltage effects,as well as long-term thermal aging.The MOA valve plate can deteriorate due to vibration,high temperature,moisture intrusion,etc.The above phenomena can cause safety hazards to the operation of the lightning arrester.Timely detection and elimination of safety hazards can avoid causing safety accidents,Therefore,studying the temperature rise characteristics of the valve under typical overvoltage,the performance of the lightning arrester under long-term electrothermal aging,and the degradation performance and mechanism of the valve have important significance for improving the reliability of the traction power supply system operation.The voltage of the EMU during operation was collected,and the characteristics of overvoltage were analyzed.A network voltage simulation test platform was established to study the current response and temperature changes of the valve piece.The research shows that the maximum amplitude overvoltage type is steep wave impulse overvoltage,with a maximum peak value of 139.0 kV;The maximum probability of over phase overvoltage is 51.43%.After 1 hour of continuous pressurization,the maximum temperature rise of the valve plate under the action of excessive phase voltage is 5.2℃;Under the action of pantograph lifting overvoltage,the maximum temperature rise of valve plate is 5.1℃;Under the action of higher harmonic voltage,the maximum temperature rise of the valve piece is 23.6℃;Under the action of steep wave impulse voltage,the maximum temperature rise of the valve plate is 11.2℃;The research shows that under the action of voltage waveforms containing higher harmonics,the temperature rise of the valve plate increases significantly with the increase of the number of harmonics.Under the action of other overvoltage waveforms,the current of the arrester valve plate has little relationship with the waveform,and is determined by the voltage amplitude.The temperature rise is determined by the voltage and the power generated by the current.The electrical aging test of the roof arrester was conducted,and the electrical performance of the arrester with different aging degrees was tested.The arrester aged for 1000 hours was disassembled and inspected.The research shows that with the increase of aging time,the leakage current of lightning arrester U1mA gradually increases,and the leakage current at 0.75 times U1mA gradually decreases.During disassembly inspection,it was found that there were many micro cracks on the surface of the epoxy cylinder,and SEM testing showed that the porosity of the aged zinc oxide valve piece increased.In order to quantitatively evaluate the performance changes of roof lightning arresters during thermal aging,the entropy weight method was used to calculate the weight of key electrical characteristics during thermal aging.The calculation results show that U1mA has the largest weight,which is 0.3216;Weighting electrical performance based on the objective relationship between various electrical performance parameters can provide a basis for accurately evaluating the status of on-board zinc oxide lightning arresters.A series of simulation tests have been carried out on the deterioration of the arrester valve under complex operating conditions,and their performance tests have been carried out.The test results show that compared to the new valve piece,the surface of the valve piece subjected to vibration aging has different degrees of wear,and the glass fiber layer near the discharge port of the epoxy cylinder has been significantly damaged.After testing,the insulation resistance of the valve piece insulation layer has decreased by up to 166MΩ.A DC electrical performance test has been conducted on the valve piece,and the results show that the uniformity between the valve pieces has decreased;After high-temperature aging,the appearance of the valve piece changes,and it is calculated that compared to the new valve piece,the deep trap density of the insulation layer on the side of the valve piece after high-temperature aging significantly decreases,and the insulation performance decreases.The DC electrical quantity test shows that the valve performance fails after the temperature reaches 800℃;The results of boiling aging show that even after the insulation sheath is damaged,the electrical performance of the boiled lightning arrester and the disassembled valve piece is fully dried,and still meets the standard.After disassembly,it is found that there are traces of water intrusion in the aluminum spray layer and side insulation layer of the valve piece.Although the electrical and pneumatic performance of the valve piece remains almost unchanged after drying,a water intrusion test is conducted with the new valve piece,and the results show that the DC reference voltage of the valve piece decreases significantly after boiling aging. |
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