Research On Grounding Impedance Testing Technology Of Live Tower

With the rapid development of smarrt grid,lightning tripping accidents of tower lines caused by excessive grounding impedance of live poles and towers occur from time to time.This phenomenon has attracted more and more attention of the power industry.Ensuring that the tgrounding impedanc.e of l.ive pole towers meets the requirements of regulations is of great engineering significance to the safe and stable operation of power system and the prevention of accidents.Therefore,ac.curate and effective measurement of grounding impedance of live pole towers is essential.Firstly,this paper analyses the common measuring technology of grounding impedance of live pole and tower in detail.Aiming at the shortcomings of large error,disconnection of grounding lead and high labor intensity,a frequency conversion on-line measuring method of grounding impedance of live pole and tower is designed.An equivalent circuit model for measuring grounding impedance of live pole tower with continuous grounding leads is established.The law of grounding impedance varying with current frequency is analyzed,and the necessarv conditions for on-line measuring grounding impedance are deduced,Multisim software is used to simulate and analyze the main factors affecting tlhe measurement of grounding impedance(tower number,grounding resistance,lightning arrester inductance,equivalent inductance of grounding body),and to verify the feas.ibility of frequency conversion on-line measurement method.Secondly,based on the theory of frequency conversion on-line measurement method,the device of frequency conversion on-line measurement system for grounding impedance of live pole tower is designed and implemented.Based on DDS technology and Howland current pulmp principle,a variable frequency excitation current source is designed.A hardware measurement system is constructed by combining data acquisition module,preprocessing module,CPU module and display module.Based on the fiunctional requirements of the measurement system,the software program of the hardware is compiled and debugged by using CCS(Code Composer Studio)software.Realize the assembly,construction and testing requirements of the measurement system.Finally,the validation experiments under laboratory conditions and the field tower environment measurement experiments are completed by using the designed measuring system.Under laboratory conditions,the equivalent analog circuit is measured and compared with the high frequency parallel method.The results show that the on-line frequency conversion measurement method can realize the accurate measurement of the grounding impedance of the live pole tower,and the overall accuracy is better than the high frequency parallel method.The tripole method is used as the scalar value of the measurement results to measure the pole tower environment in Xi'an;parallel with the clamp meter method and the high frequency parallel method.Compared with the three-pole method,the on-line frequency conversion method has better accuracy than the clamp meter method and the high-frequency parallel method,and the relative error is about 5%,which meets the engineering measurement error requirements.