In order to formulate relevant standards for the lightning protection grounding resistance of urban rail transit, it is necessary to further carry out actual measurement research on the grounding resistance of urban rail transit lines, count more test samples, deepen theoretical analysis, and summarize the test methods and test limits requirements for urban rail transit. 

  When testing the impulse ground resistance of the grounding body of the urban rail transit ground line, in order to avoid affecting the safety of the equipment in operation, please refer to the relevant requirements in DL/T 266-2012, and the output voltage of the impulse signal source should not be lower than 2000 V. The output surge waveform should satisfy the impulse voltage wave head/wavelength time within 1～5μs/50～80μs.

  The inrush current is affected by the inductive effect during the discharge process, and the discharge range of the grounding body is limited. According to the actual measurement results, the discharge range of the grounding body of the urban rail transit ground line is within 100m.

  The impulse voltage will have a significant impact on the test results of impulse grounding resistance, and present a non-linear corresponding relationship, which is caused by the spark discharge effect in the soil as the amplitude of the impulse voltage increases.

  During the actual measurement, it is found that it is often difficult to find an ideal open test environment around the rail transit line in the urban environment. When there are large buildings around the line, the impact ground resistance test result is easily affected by the interference of the grounding body of the surrounding buildings. Therefore, it is necessary to carry out relevant research to avoid the interference influence caused by the surrounding buildings of the line on the test results, and obtain the test method in the urban environment.

  The height of the test cable from the ground will have a significant impact on the results. Insulating materials shall be used as far as possible to keep the test cable at a certain height from the ground; At the same time, the cables are separated at a certain angle to reduce the influence of electromagnetic coupling between cables on the test results.