Fault Mechanism And Optimal Design Of Voltage Transformer On 35kV Standby Interval For Subway Power Supply

The 35 k V voltage transformer on the standby interval is an important electrical equipment in the subway power supply system.It is mainly used to replace the faulty voltage transformer on the 35 k V bus,and it can also play a great role in developing new lines.However,in recent years,the voltage transformers on the central line and the backup interval of the subways in Nanjing and Shenyang have all failed during operation,which seriously affected the normal operation of the subway trains.Therefore,this paper mainly studies the failure mechanism of the influence of the power quality of the system on the voltage transformer,analyzes the reasons for the failure of the voltage transformer in the backup bay,and makes an optimal design.This paper firstly introduces the basic situation of the subway power supply system and the concept of the backup interval,and explains that the backup voltage transformer works on the backup interval at the end of the 35 k V busbar in the way of hot backup.The power quality of the 35 k V bus is analyzed emphatically,and it is found that if it is affected,power quality problems such as harmonics,DC components,overvoltage and line faults will occur.Secondly,the failure mechanism of the voltage transformer was analyzed,and it was found that in the follow-up accident investigation of the voltage transformer failure,the insulation of the voltage transformer was mainly burned out on the primary side.And analyzed and calculated the influence of the power quality problem on the busbar on the failure of the voltage transformer,and then analyzed the reasons for the failure of the voltage transformer on the backup bay.In case of overvoltage,multiple overvoltage processes may occur to the standby interval voltage transformer,which will accelerate insulation aging.Thirdly,the simulation model of the voltage transformer on the 35 k V main line and the backup interval of the subway is established in the MATLAB software,and the situation when the above-mentioned power quality problems occur is simulated.Simulation analysis verifies the correctness of the previous theoretical analysis.Finally,according to the analysis of the fault mechanism of the voltage transformer on the backup bay,an optimization scheme is given: externally,by grounding the neutral point of the primary side of the backup voltage transformer through a nonlinear resistor and a saturable inductance,it can play a good role in the separation of Voltage and current limiting effect;internally,the scheme of increasing the wire diameter of the primary side winding of the standby voltage transformer and installing non-magnetic clips in the iron core not only increases the limit capacity,but also improves the ability of the primary winding to resist overcurrent.,also eliminates the residual magnetism in the iron core and improves the excitation characteristics.After the scheme is given,the rationality of the scheme is verified by simulation.,The optimized backup voltage transformer was put into use in Harbin Metro,and no fault has occurred so far.During the follow-up inspection,it was found that its working condition was still very good,which confirmed the feasibility of the optimization plan.