The main grounding network of power plants and substations plays a decisive role in ensuring the safe operation of power equipment and personal safety. The grounding resistance value is an important technical indicator of the grounding grid. Due to the significant difference between the design value and the actual value of the grounding resistance, in order to have a true and accurate grasp of the grounding resistance of the grounding grid, it is necessary to measure the grounding resistance of the grounding grid. This is of great significance for accurately estimating the safety of substations and ensuring the safe operation of the power system.
When measuring grounding resistance, the following points should be noted:
1. Generally, the grounding device being measured during measurement should be disconnected from the lightning conductor.
2. The current and voltage poles should be arranged in a direction perpendicular to the line or underground metal pipeline.
3. It should be avoided to measure the grounding resistance immediately after rain. When measuring grounding resistance, it is best to do so in spring with low rainfall or winter with low temperatures, when the soil moisture content is the lowest, the temperature is the lowest, and the electrical resistivity is the highest.
4. When using the AC ammeter and voltmeter methods, the electrode arrangement should be triangular, and the voltmeter should use a high internal resistance voltmeter.
5. The distance between the tested grounding electrode E, voltage pole P, and current pole c should meet the requirements of the measurement method.
6. The cross-section of the connecting wire used: the current line should be greater than 2.5mm, the voltage line should not be less than 1.5mm, and the current circuit should be suitable for the measured current value; the resistance of the wire connected to the tested grounding body E should not exceed 2% to 3% of R. The test lead should be insulated from the grounding body.
7. The voltage pole lead of the instrument should be kept at least 1m away from the current pole lead to avoid interference.
8. Repeatedly measure 3-4 times and take the average value.
9. When using a hand operated grounding resistance meter for measurement, interference is found and the rotation speed of the grounding resistance meter can be changed.
10. When the sensitivity of the instrument is too high in measurement, the position of the electrode can be increased to make it inserted shallower into the soil. When the sensitivity of the instrument is insufficient, water can be injected into the insertion points of the voltage and current poles to make them moist, in order to reduce the resistance of the auxiliary grounding rod.
11. The measured current should be as much as possible greater than 20A to ensure measurement accuracy.
12. When measuring the grounding resistance on live equipment, special attention should be paid: insulation gloves must be worn when loosening and restoring the grounding lead.
13. Do not touch grounding leads that are disconnected from the ground.
14. It is strictly prohibited to measure the grounding resistance of the grounding grid during thunderstorm weather or when grounding faults are found in the substation booster station.
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