Study On Method Of On-line Monitoring And Fault Early Warning Of MOA

As one of the most important over-voltage protective device in the power system,working condition and safe operation of metal oxide surge arrester have been more and more attention.The MOA is mainly used in the power system to limit lightning over-voltage from the line and internal over-voltage caused by operation,which can ensure the normal and stable operation of the system.Because of excellent nonlinear characteristics,good protection characteristics,large flow capacity,simple structure and so on,MOA is widely used in larger voltage level systems to provide greater protection margin.Although the manufacturing level of MOA is improving continuously,due to long-term impact of power frequency voltage,over-voltage and dampness,ZnO varistors will gradually become old,and the leakage current will increase and lead to higher temperature,which will eventually lead to power grid accident.Hence,in consideration of the increasing trend of MOA accident rate,in order to reduce and avoid accidents and ensure the safe operation of the system,it is more and more important to explore effective on-line monitoring and early warning methods of MOA.Firstly,the simulation model of UHV MOA is established.The potential distribution under normal working conditions and the leakage current of ZnO varistors are calculated and analyzed,and the accuracy of the simulation calculation is verified by charging test.Then,the influence of installation height of MOA equalizing ring and relative dielectric constant of ZnO varistors on the potential distribution of MOA is analyzed,and the optimization plan is put forward.Secondly,according to the structure and operation mechanism of optical fiber current sensor,combined with the use of optical fiber current method and principle of on-line monitoring method,the energizing test of MOA under different fault states is carried out.The resistive leakage current of MOA is observed and collected by optical fiber current sensor,and the change of resistive leakage current is analyzed under different faults.Finally,according to the experiment,the fluctuation ratio of MOA resistance leakage current under different fault states are calculated.Considering of the safety margin of MOA and stable operation of power system,the relationship between the resistive leakage current and the failure state of MOA is obtained.According to fault on-line monitoring of MOA,a fault warning method based onmeasuring resistance leakage current is proposed: the optical fiber current sensor is used to monitor the resistance leakage current of the ZnO varistors at different locations of the MOA in each section,and the characteristic relationship between the fault state and the resistive leakage current of MOA is used to analyse whether the detected resistance leakage current has reached the critical value of an accident.If it is,then the replacement and maintenance work of MOA is carried out.If the maximum permissible value is not met,the failure extent of MOA is judged,and the fault warning is carried out depend on its running state.