Study On Influence Of Transient Ground Potential Rise On Secondary System And Its Protection Technology

Electric secondary equipment of power system plays an important role in the power system.The normal operation of the secondary equipment has a great influence on the security and stability of the whole power system.With the digitization and electronization of the secondary equipment in the converter station,especially after the hierarchical and distributed protection structure is adopted in the control system of the converter station,a large number of them are protected,controlled,communication and other functions of various precision secondary equipment placed in the high-voltage switching field of the converter station,resulting in the secondary system of the converter station is greatly increased the probability of interference,in addition,the converter station due to lightning strikes,short-circuit fault,the switching operation will cause the grounding grid to be impacted by the high frequency current,which will make the grounding grid shows the phenomenon of uneven distribution of transient grounding potential.The transient potential rise caused by lightning strike is characterized by high voltage amplitude and wide frequency range.The transient potential will be coupled to the core wire by the cable sheath and invade the secondary system.The secondary equipment is seriously affected.At present,the faults caused by the rise of the transient grounding potential in the secondary loop often occxr,which makes a serious threat against the power network and affects the stable operation of the power system.At the same time,there is no uniform standard for shielding grounding design of secondary cable in converter station,and the configuration of overvoltage protection device for secondary equipment is basically not.Therefore,the transient grounding potential rise of grounding network of converter station is carried out.It is of great significance to study the influence of the secondary system and the suppression measures.Based on the multi-segmented secondary cable structure of AC filter field in converter station,the calculation model of transient potential rise to secondary cable port disturbance voltage is established by using PSCAD software,and the distribution rule of secondary cable port disturbance voltage is calculated.The secondary cable port disturbance voltage test is carried out in the UHV converter station AC filter field,and the test data and simulation data are compared and analyzed to verify the feasibility of the simulation model.On the other hand,based on the transient calculation model of secondary cables,the influence of different grounding modes of multi-segment secondary cable shielding layer and armored layer on the interference voltage of secondary cables in the ac filter field of uhv converter station is studied.The suppression effect of different overvoltage protection devices on secondary cable interference is studied from the point of view of suppressing secondary cable port disturbance voltage.Finally,the protection of transient grounding potential rise in the secondary system of UHV converter station is studied,which mainly includes the coordination of surge protectors,including interstage coordination,coordination with the protected load characteristics,taking into account the actual situation,the different operation voltage of the pre-stage and the last stage surge protectors and the different cable length will affect the matching effect of the surge protector,so the different operation voltage and cable length of the pre-stage and the last stage are selected respectively,the simplified circuit is used to analyze and calculate the matching effect,and on this basis,the physical experiment is carried out.Comparing the experimental results with the simulation results,it is found that the two results are approximately:in agreement with the results of the simulation.As a result,the correctness of the simulation calculation is proved.The research results in this paper can provide a valuable reference for the design of protection measures for transient grounding potential rise in secondary system of converter station,and have practical value in restraining transient grounding potential rise.