Explain the measurement method of the large-scale ground network grounding resistance tester

Explain the measurement method of the large-scale ground network grounding resistance tester

Measurement wiring

1. Ground network test

Figure 3 Wiring diagram of three-pole method measurement

Measuring current wire D: wire diameter ≥1.5mm2, length is 3 to 5 times of diagonal length of ground network;

Measuring voltage line 1: wire diameter ≥ 1.0 mm2, length 0.618D;

Measuring voltage line 2: Connect to the measured ground network;

Measuring ground wire: connect to the measured ground network.

Figure 4 Four-pole method measurement wiring diagram

When measuring with the four-pole method, two connecting wires are drawn from the ground piles of the ground net and are respectively connected to the two terminals of the voltage pole P2 and the ground net C2 of the instrument, and then tested according to the measurement operation steps. The instrument will automatically eliminate wiring errors during the four-pole measurement.

Note: The measuring line is configured by the user according to the size of the ground network. If the company's wiring is required, it will be charged separately.

2. Test of contact voltage and contact potential difference

The wiring diagram for measuring the contact voltage is shown in Figure 5 below. The test can be carried out as follows.

Figure 5 Wiring diagram of contact voltage measurement

A ground pile is driven far away from the grounding device as a current pole, and the distance of the current pole from the edge of the grounding device is still more than 4 times the length D of the large diagonal of the grounding device.

Connect the C terminal of the instrument panel to the current with a wire. The structure of the large-scale grounding network resistance tester then connects the E terminal of the instrument to the device under test.

The P1 terminal of the instrument is connected to the Pa point on the equipment structure, and the height of Pa from the ground is 1.8 meters. The P2 terminal of the instrument is connected to the electrode Pb of the analog foot. The electrode can be a metal disc with a diameter of 500px wrapped with a damp cloth and pressed with a heavy object. The distance between the electrode center and the edge of the device is 1 meter.

The equivalent human body resistance Rm is connected in parallel between the P1 and P2 terminals of the instrument. The large-scale grounding network ground resistance tester generally takes Rm = 1.5KΩ. After checking the wiring is correct, turn on the instrument power, choose to perform "ground impedance measurement", and then set the test current , The instrument starts to measure, after the measurement is completed, the impedance value Z can be read from the LCD screen.

Then calculate the contact voltage Uj according to the following formula

Uj = Z * Is

Where Is is the single-phase ground fault current of the system in the grounding device under test.

In the above measurement, if the equivalent human body resistance Rm is not connected in parallel with the voltage input terminal of the instrument, the result obtained is the contact potential difference.

3. Step voltage and step potential difference test

The wiring diagram for measuring the step voltage is shown in Figure 6. The test can be carried out as follows.

Figure 6 Wiring diagram of step voltage measurement

A ground pile is driven far away from the grounding device as a current pole, and the distance of the current pole from the edge of the grounding device is still more than 4 times the length D of the large diagonal of the grounding device.

Connect the C terminal of the instrument panel to the current with a wire. Then use a wire to connect the E terminal of the instrument to the ground lead of the device.

The P1 and P2 terminals of the instrument are connected to the electrodes Pc and Pd of the simulated human foot. The electrode can be a metal disc with a diameter of 500px wrapped with a damp cloth and pressed with a heavy object. The center distance between the two electrodes is 1 meter.

The equivalent human body resistance Rm is connected in parallel between the P1 and P2 terminals of the instrument, generally Rm = 1.5KΩ. After checking the wiring is correct, turn on the instrument power, choose to perform "ground impedance measurement", set the test current, the instrument starts measurement, the measurement is completed The impedance value Z can be read from the LCD screen.

Then calculate the step voltage Uk according to the following formula

Uk = Z * Is

Where Is is the single-phase ground fault current of the system in the grounding device under test. In the above measurement, if the equivalent human body resistance Rm is not connected in parallel with the voltage input terminal of the instrument, the result obtained is the step potential difference.

4. Soil resistivity test

With this instrument, the unipolar method or the quadrupole method can be used to measure the soil resistivity. The following uses the quadrupole method as an example. The wiring for measuring soil resistivity is shown in Figure 7.