Research On Lightning Electromagnetic Radiation For Depot Facilities By FDTD Method

Lightning is an essential part of natural physical process.The strong electromagnetic radiation generated by lightning is a strong source of electromagnetic interference.It can not only affect the electromagnetic environment in depot area,but enter depot power systems by coupling,causing high voltage power supply line outage,DCS crash and other accidents.These do great harm to communication equipment and power systems.Therefore,knowing the radiation circumstances causing by LEMP to surroundings,and its coupling to power systems has an important practical significance to lightning protection in depot area.This paper started with the construction of lightning return-stroke model,simulated the measured lightning current in Beijing,and conducted spectral analysis to it.The results show that the energy of this lightning current mainly appears in the range of ULF and VLF,whose frequency is under tens of kHz.In order to reduce the harm of lightning to oil depot automation systems,RLC filter can be used to discharge lightning(Low frequency)and protect useful signal(High frequency).Then the paper premising on the lightning current model,using FDTD method,calculated the electromagnetic field generated by the current in depot area and underground space where underground tank exists.The calculation results show that the ground electromagnetic field is mainly affected by the lightning current within 500 m height.Its strength increases rapidly in the rising phase of lightning current.Within 25 m radial distance from lightning return-stroke channel,the strength of ground electromagnetic field is large and decay about one order of magnitude with increasing radial distance.When the lightning electromagnetic wave propagates in the underground,the soil has a great attenuation on vertical electric field component,and the strength of Ez in underground space is higher than which contacting with the soil.Finally,the paper simplified the depot power system into load resistors at the terminal of a cable and power lines only considering inductance effects,calculated their induction to the near lightning electromagnetic field by FDTD method,and proposed some lightning protection measures.The calculation results show that the lightning induced peak voltage and current on load resistors can up to hundreds of kilo-volts and hundreds of amperes,and after the spike,there is an oscillating process whose oscillating voltage peak is still up to ten kilo-volts.The coupling effect enhances with increase of the cable length.The surge voltage,which is induced on a power line by inductive coupling,appears in the rising phase of lightning current.The induced voltage on a power line and induced current at the end of a power line will be higher when the line is laid radially to the lightning return-stroke channel or perpendicularly to the floor,and their peak value can up to thousands of volts and hundreds of amperes.