Research On EMI Of GIS On Very Fast Transient Overvoltage

In recent years,the voltage level of power systems has gradually evolved to ultra-high voltage levels.Gas Insulated Substation(GIS),as one of the important components of the power system,participates in the daily operation of the power grid.The operation of the disconnector switch in GIS will generate over-voltages with high amplitude,steepness,and fast frequency in the pipeline,that is,Very Fast Transient Over-voltage(VFTO).When propagating in the pipeline,the discontinuity of the wave impedance is encountered,which will generate refraction and then couple to the shell,causing the shell potential to rise,that is,the enclosure voltage(TEV).Externally radiated electromagnetic waves will cause a strong transient electromagnetic field in space.Due to the intelligent development of GIS,such as the application of digital technology and computer hardware,the secondary equipment used for measurement,control,and protection is installed near the primary equipment,so the transient space electromagnetic field caused by the operation of the disconnector switch will lead these secondary equipment to generate strong electromagnetic interference,which is likely to cause damage to related equipment,and then affect the normal operation of the power system.Therefore,the electromagnetic interference problem of GIS space and its secondary equipment under VFTO deserves further study.Based on the calculation of the GIS transient overvoltage under the operation of the disconnector switch,the distribution of the spatial electromagnetic field generated by the VFTO in the GIS space using a combination of field and road is studied.The factors that affect the GIS spatial electromagnetic field are analyzed.In addition,the effects of radiated interference generated by VFTO on electronic transformers are studied,and the electromagnetic interference factors affecting electronic transformers are analyzed.The main research contents of the article are as follows:Aiming at the problem of GIS transient over-voltage calculation under the operation of disconnector switch,this paper takes 550 kV GIS as the research object.A typical operation mode is selected,and the key equipment in GIS is modeled equivalently based on the multi-conductor transmission line theory.A complete transient circuit model is built on the simulation software EMTP,and the transient overvoltage formed under the operation of the disconnector is calculated.The calculation results show that the most serious place of VFTO is 2.09 p.u on the power supply side of the circuit breaker,and the most serious place of TEV is 0.102 p.u on the outlet bushing.The frequency of the transient voltage waveform is high and the composition is complex.The distribution of spatial electromagnetic field generated in VFTO on GIS space is studied.The electromagnetic transient simulation software CST(Computer Simulation Technology)is used to simulate the distribution of the GIS spatial transient electromagnetic field and obtain the 550 kV GIS spatial transient electromagnetic field distribution under the operation of the disconnector switch.The simulation results show that the electric field near the GIS line can reach a strength of more than ten kilovolts per meter,and the magnetic field strength can reach tens of amperes per meter.Compared to the magnetic field,the electric field can cause greater interference to the GIS;the frequency also has a certain degree of field strength.The field strength decreases with increasing frequency.The distance has a significant effect on the field strength.The field strength near the GIS line changes significantly with increasing distance.The value of the field strength is large.As the distance increases,the field strength value becomes stable,and the field strength value is smaller.Therefore,the secondary equipment should be arranged away from the line,and shielding measures must be taken to ensure safety if it cannot be avoided.The effect of radiated interference generated by VFTO on electronic current transformers is investigated.A three-dimensional simulation model of the electronic current transformer is built in the CST,and the electromagnetic field distribution radiated by the VFTO into the electronic current transformer is obtained by simulation calculation.The simulation results show that the electromagnetic field generated by VFTO can penetrate the disk to the inside of the collection box,and generate electromagnetic interference to the equipment inside the collection box.The electric field strength inside the collection box has reached ten kilovolts per meter,and the magnetic field strength is at the tens of amperes per meter.The electric field plays a dominant role in electromagnetic interference,which can be seen.In addition,the influence of the disk radius and thickness on the electromagnetic field inside the collection box is considered.The results show that the disc radius of the terminal has a significant effect on the electromagnetic field inside the collection box.Reducing the radius,the field strength inside the collection box will become smaller.The thickness of the disk has no significant effect on the electromagnetic field inside the collection box.