Study On Initial Unbalanced Current Adjustment Of 500kV Filter In ±500kV Converter Station

Breakdown of capacitor is the most common fault in AC filter.Capacitor breakdown will change the filter characteristics of AC filter,and some of the capacitor breakdown will cause overvoltage running of the rest capacitors.If can not configure the appropriate protection of the signal or the removal in time,it will cause the avalanche effect of capacitive components and the expansion of the accident.Therefore,in engineering applications,in order to monitor the filter in the electrical capacitor is breakdown,the capacitor group will be in accordance with the H type combination,than monitor the internal faults of the capacitor by using the unbalanced current.But if the AC filter in service havn't the fault and unbalanced current value is too large,it is likely to cause the imbalance of current protection.At this point,the capacitor value of the AC filter is required adjustment to make the initial unbalanced current within the allowable range.In the operation of the AC filter banks,when the imbalance current exceeds the standard,it need adjusting the AC filter bank recombination scheme,according to the traditional method of high test,workload is big and the uncertainty is high.There are technical personnel using the Matlab simulation software,combined with the actual operation and maintenance of Deyang converter station,put forward a new set of AC filter unbalanced current adjustment strategy.The new strategy was constructed according to the mathematical model of field measured data,the simulation optimization principle and Matlab software,high voltage capacitor group after adjustment,determination of the unbalanced current between bridge arms using field test,verify the reliability of the simulation and optimization results.According to the results of the simulation analysis and field test,the new method is correct,and it can achieve the goal of improving work efficiency.But because there are many factors that affect the unbalance current of the capacitor group,such as environment and stray capacitance,the different between the field test and the result of the simulation is quite large.The biggest advantage between this method and the traditional method is to use mathematical tool Matlab to confirm the need to replace the capacitor,so that the efficiency is be improved.But it is not accurate to calculate the size of the unbalanced current after the adjustment.Found in the practice of Yunnan power grid 500 k V Yongren converter station,according to the traditional method of adjusting capacitor value cause not only maintenance workload,but also high uncertainty.When the value of each bridge arm capacitance unbalance is lower than 5/10000,the unbalanced current also exceed the standard.After the pen team repeated efforts,several actual experiment confirmed: traditional method according to adjust capacitor can not reduce the size of AC filter initial unbalance current,low voltage analog method does not accurately reduce the power of AC filter initial unbalance current,modified low voltage analog method can be in one step complete adjustment and accurate control of the unbalanced current size.This paper takes Yunnan power grid + 500 kV Yongren converter background,related theory has been well verified in the treatment of AC filter initial unbalance current is too large.