Research And Application Of A New Technology On Grounding Resistance Measurement Of Grounding Grid

Grounding is an important measurement to ensure the safe and reliable operation of power system,and to ensure the safety of electrical equipments and operators.The grounding resistance parameter is a macroscopic quantitative index to measure the discharge capacity of the grounding grid,which is the most important characteristic parameter of the grounding grid.Its size is directly related to the performance of the grounding grid.Non-frequency method uses variable frequency power supply,measuring grounding resistance under frequency deviating from power frequency,which can effectively eliminate power frequency and high frequency interference in the earth,so it has been widely applied.The grounding grid of power plant and substation is large,in the grounding resistance measurement,the voltage and current measuring lines need to be arranged fairly long.In order to save time and manpower,it's frequent to make an overhead transmission line out of running and use the conductor wire as the voltage and current measuring lines.Due to the electromagnetic coupling between the lines,the testing current flowing through the current line will produce different frequency interference voltage in the voltage line,affecting the accuracy of measuring voltage.If making one of the multiple transmission lines on the same pole out of running and use it as the measuring circuit,electromagnetic coupling is also present between measuring circuits and other normal running lines on the same pole,inducing different frequency interference voltage in voltage line and bring error to the measurement result.For the grounding grid of running power plants and substations,only a part of testing current injected into the grounding grid is scattered into the ground through the measured ground grid,the other part of testing current outflows into other ground loops connected to the grounding grid.The influence of shunt should be considered in the measurement of grounding resistance.Based on straight-line non-frequency method,this paper analyzes the components of the measured voltage under different measurement conditions,and deduces the accurate expression of the measured voltage in the corresponding case.A new method of grounding resistance measurement is proposed considering the influence of the electromagnetic coupling between the measuring lines,and between the measuring circuit and other normal running lines on the same pole,by changing the position of the electrode and measuring in several times,so as to eliminate the influence of the coupling interference by using the measured data.In addition,the various diversion paths of the grounding grid are analyzed,and the necessity of shunt measurement is pointed out.Then,building models in the PSCAD simulation environment and programming using MATLAB software to analyse simulation data in order to verify the accuracy of the new method of grounding resistance measurement.The shunt model is established by considering different flow patterns,and the main factors affecting the shunt effect of the grid are analyzed.This paper introduces the design idea of the grounding resistance measuring device based on the new measuring method,describes the process of the development of hardware system and software system.Finally,the new measurement method is put into use in the grounding resistance measurement using the developed measuring device,and the theoretical measurement method and the measuring device are tested by the field test results.This paper uses the research method to discuss and verify the new method of grounding resistance measurement combined with theoretical research,simulation test,device development and field measurement.Simulation and field measurement results demonstrate the accuracy of the proposed method and the reliability of the developed device.It is reasonable to assume that the new measurement technique has a high engineering application value.