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Reasons for inaccurate ground resistance test

time:2021/2/25   source:华天电力  reading:591 time

The reasons for the inaccurate ground resistance test in lightning protection detection and the treatment methods. In the power lightning protection detection, there are many factors that cause the ground resistance readings to be inaccurate. In summary, there are generally the following reasons:

1. When detecting high-rise buildings, the used wire is too long and too thick, which will increase the wire resistance and induced voltage and cause measurement errors. At this time, wires with relatively low wire resistance should be used to minimize the measurement error.

2. The penetration depth of the iron drill should be greater than 1/4 of the length of the iron drill, otherwise, a test error will occur. Therefore, the iron drill should be drilled as deep as possible during testing.

3. When the measured grounding electrode is in the "common ground", due to poor insulation or short-circuit of the equipment, the grounding device generates a certain ground voltage to the ground, which makes the reading unstable during measurement. At this time, the power should be cut off for testing, or The place where the card is disconnected is disconnected for detection to avoid the influence of ground voltage on the detection.

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4. In case of poor contact, rusty or broken test wire, the test will find the phenomenon of intermittent connection or large resistance. At this time, the rust should be removed first. If it still cannot be ruled out, check and test with the resistance file of a multimeter. Wire continuity.

5. Since the grounding resistance tester is to test the ground resistance of the grounding body through the iron solder transmitting and receiving current, so when the distance between the two iron solders and the distance between the two solders and the grounding body is too close, mutual interference will occur. Error, therefore, in the measurement, the grounding body, voltage electrode, current electrode are arranged in sequence, and the three points are in a straight line and are 20 m apart from each other.

6. When the measured place has materials such as cushion soil or sand, the measurement error is caused by the difference in the resistivity of the upper and lower layers of the soil. At this time, the iron should be deepened to make it fully contact or avoid the soil under the cushion. Open the soil layer to reduce the measurement error.

7. When the tested grounding devices and metal pipes and other metal objects are buried in the ground more complicated, the current direction of each pole of the measuring instrument may be changed to cause poor or unstable measurement. At this time, you should first understand the layout of the grounding body and the metal pipe , Choose a place with relatively small impact for measurement.

8. The measurement is inaccurate due to the potential difference or strong magnetic field on the ground. At this time, you should try to stay away from places with large potential differences or strong magnetic fields. If it is unavoidable, the detection line should be relatively shortened to reduce measurement errors.

9. When the operator is in use, failure to follow the instructions, failure of the instrument without timely maintenance, inaccuracy of the instrument or long-term lack of identification, etc., will also cause measurement errors.

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