At present, in the electric power system, the test of the grounding resistance of the large-scale grounding grid currently mainly adopts the power frequency high current three-pole method. In order to prevent the power frequency interference generated during the operation of the power grid and improve the accuracy of the measurement results, the insulation preventive test regulations stipulate that the test current of the power frequency high current method shall not be less than 30 amperes. As a result, many problems such as heavy test equipment, complicated test process, heavy work intensity of test personnel, and long test time appeared.

The grounding resistance tester of the earth network can test the multi-purpose models of substation ground network (4Ω), hydro-thermal power plant, microwave station (10Ω), and lightning rod (10Ω). It adopts a new variable frequency AC power supply, and adopts measures such as microcomputer processing control and signal processing. , It solves the anti-interference problem in the test process, simplifies the test operation process, improves the precision and accuracy of the test results, and greatly reduces the labor intensity and test cost of the test personnel.

The earth grid grounding resistance tester is mainly composed of a different frequency power supply that provides a test current, a current and voltage measurement circuit, and a microcomputer measurement and control system. The instrument measures the ground impedance by measuring the ratio of the potential rise of the grounding device to the current flowing into the grounding device.

The different frequency constant current power supply of the earth grid ground resistance tester can output a sine wave test current with a frequency of 45Hz or 55Hz, and the output frequency is controlled by the microcomputer system. After isolation, the output is output through the E and C terminals on the instrument panel. The voltage amplifier is a high input impedance amplifier, which amplifies the voltage at both ends of P1 and P2 and sends it to the filter. The current amplifier amplifies the current signal obtained from the current transformer and sends it to the filter. The filter is used to filter out interference signals, and only allows 45Hz and 55Hz signals to pass. The A/D converter is used to convert voltage and current signals into digital signals for analysis and processing by the microcomputer system.

After the user starts the ground impedance measurement, the earth grid ground resistance tester first turns on the different frequency power supply to output a current with a frequency of 45Hz. After the current stabilizes, the microcomputer system obtains the voltage and current waveform data through the A/D converter and performs digital filtering. After calculating the voltage V45 and the current I45 and their phase difference, the impedance Z45, the resistance component R45 and the reactance component X45 are further calculated. Then, the output frequency of switching the different frequency power supply is 55Hz. After the same steps, the impedance Z55, the resistance component R55 and the reactance component X55 can be calculated. Take the average value of Z45 and Z55 as the power frequency grounding impedance Z50. *After that, turn off the inter-frequency power supply and display the measurement results on the LCD screen. Therefore, when measuring impedance, the instrument measures the ratio of the voltage between the two voltage input terminals P1 and P2 to the output current of the power supply.