Large-scale grounding grid grounding resistance tester is suitable for testing the power frequency ground impedance, contact voltage, step voltage, and other power frequency characteristic parameters and soil resistivity of various grounding devices. This instrument adopts different frequency anti-interference technology, which can accurately measure the data under the power frequency of 50Hz in a strong interference environment. The maximum test current is 5A, which will not cause the potential of the grounding device to be too high during the test. At the same time, it also has a strong anti-interference ability, so it can be measured without power failure.

When measuring the grounding device, due to various interferences such as unbalanced zero-sequence current and radio frequency, the test results have great errors. In particular, the ground impedance of a large grounding network is generally small, and the relative error caused by interference is greater. In order to reduce the impact of on-site interference, there are two main methods currently used, one is to increase the test current, and the other is to use the inter-frequency method. One method is to increase the signal voltage and signal current by increasing the test current, thereby improving the signal-to-noise ratio and reducing the measurement error. Due to the large test current used in this method, the equipment is very cumbersome, and the wiring is labor-intensive, time-consuming and labor-intensive.

This paper introduces a method for measuring the grounding resistance of the grounding grid at different frequencies. This method can obtain stable and reliable measurement results under the condition that the frequency of the test current is equivalent to the power frequency of the system. Analyzed the source and characteristics of external interference, combined with the results of simulation test and field measurement, studied and discussed the influence of the test current frequency and the arrangement of the measurement leads on the Z, R and X of the test results.

There are power frequency current method and different frequency current method for measuring the grounding resistance of the ground grid. The former is a traditional method. The power frequency test current, test power supply capacity, and current line cross-section are all large, and the equipment is bulky. The frequency range of the test current of the different frequency measurement method used in the past ten years is about 40-250Hz. Because the test frequency is closer to the power frequency, the more difficult the hardware and software of the measuring instrument is. Therefore, the test frequency of most different frequency test instruments is far away from 50Hz. The equivalence of the different frequency test results and the power frequency test results is of concern. First, a unique hardware and software anti-interference method is developed to make the test frequency quite close to the power frequency, and stable and reliable measurement results can be obtained.