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Inaccurate grounding resistance readings

time:2021/4/9   source:华天电力  reading:868 time

Causes inaccurate detection of ground resistance or unstable or even negative value. , Because the ground resistance tester is composed of many precision electronic components and has a relatively long detection line, under the influence of bad environment and operation, measurement errors are often caused, and it is difficult to confirm the accurate value of the measured ground resistance. The following factors:


1. There is a large potential difference on the ground surface, and there are independent grounding in many places, such as the grounding of transformers in factories and complex buildings. Due to various reasons, the grounding resistance becomes larger, the insulation of the transformer itself becomes poor, and leakage occurs, which makes the grounding. There is a potential difference around the pole. If the detection rod is placed around it, it will affect the measurement accuracy.


2. The measured ground electrode itself has alternating current (the electrical equipment is not well insulated, some leakage caused by short circuit, and there is interference from the parallel high-voltage power supply near the down conductor); the structure of the earlier early buildings was rather chaotic, and the wiring Disorderly, and sometimes even the potential difference of the ground zero line is above 100V, which directly affects the measurement error of the ground resistance.


Earth Resistance Tester.png


3. Poor contact (including the instrument itself): The wiring connection of the ground resistance tester is easily broken due to frequent bending and use, and it is difficult to find due to the existence of the protective cover, which causes the phenomenon of intermittent disconnection; in addition, due to detection The rods and alligator clips have been used for a long time, and there are oxidation and corrosion phenomena, which can also cause poor contact; if the measured ground electrode is seriously oxidized and rust-free, it will also affect the measurement reading.


4. There are strong electromagnetic fields emitted by transmitters, antennas, etc. nearby: near high-power transmitting bases, such as mobile, microwave, BP machines and other communication sites, high-voltage substations and high-voltage lines, high-power equipment frequently starts place.


5. When the grounding device and the metal pipeline are buried in a complex place, it can also cause poor or unstable grounding resistance measurement, such as gas stations, chemical plants, etc., due to the complex layout of underground metal pipelines, when connected according to the normal detection, the underground metal appearance is unreliable Existence actually changes the direction of the current at each end of the measuring instrument, which often causes the measured value to be zero or negative. If there are different soil resistivities in the same site, this phenomenon can also be caused.


6. When detecting high-rise buildings, the long detection line induces voltage and causes detection errors. At the same time, the long line itself also has a cable resistance.


7. When using sandy soil with high soil resistivity and poor water absorption as the foundation cushion of the entire building, the ground resistance measured is often too large.


8. The operation is not carried out in accordance with the method specified in the instruction manual, the instrument itself is improperly maintained, and the instrument is used with disease or over-inspection.

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