Detection of grounding resistance reading inaccurate condition analysis

First, causes the grounding resistance to be inaccurate or the indication value is unstable or even has the negative value reason
Due to the grounding resistance detector is composed of many precision electronic components, there are relatively long detection lines, under the influence of adverse environments and operations, often lead to measurement error, it is difficult to confirm the exact value of the measured grounding resistance, it mainly has the following factor:
(1) There is a large potential table at the surface, and there are many independent groundings. For example, transformers, such as factories and comprehensive buildings, are grounded. Due to various reasons, the grounding resistance becomes large, the insulation of the transformer itself deteriorates, and leakage occurs. Potential differences occur around the grounding electrode. If the detection rod is placed around it, it will affect the measurement accuracy.
(2) The ground electrode under test has its own alternating current (the insulation of the electrical equipment is not good, the leakage phenomenon is caused by some short circuits, and the interference of the high-voltage power supply connected near the downline); the structure of the previous early buildings is rather chaotic. The wiring is messy, and sometimes even the zero line potential difference is above 100V, directly affecting the grounding resistance measurement error.
(3) poor contact (including the instrument itself): grounding resistance tester wiring connection, due to the use of often bent, easy to break, and because of the existence of protective cover, it is difficult to find, resulting in the phenomenon of breaking time; In addition, due to Detecting rods and crocodile use a long time, there are oxidation corrosion phenomenon, but also can cause poor contact; if the measured grounding pole oxidation serious bad embroidered, it will also affect the measurement readings.
(4) Strong electromagnetic fields emitted by nearby transmitters, antennas, etc.: In the vicinity of high-power transmitting bases, such as mobile, microwave, and BP machines, high-voltage equipment, frequent high-voltage equipment near the high-voltage substations Starting place.
(5) Grounding devices and metal pipes buried in a relatively complex way can also cause poor or unstable ground resistance measurement, such as gas stations, chemical plants, etc., due to the complexity of underground metal pipe layout, according to the normal inspection connection, underground metal road appearance The existence of this, in fact, changes the direction of the current at each end of the measuring instrument, often causing the measured value to be zero or negative. If there is a different soil resistivity at the same site, this phenomenon can also be caused.
(6) When detecting a high-rise building, an excessively long detection line induces a voltage and causes a detection error. At the same time, the long line itself also has a wired resistance.
(7) When the soil with high resistivity and poor water absorption is used as the foundation cushion for the whole building, the measured grounding resistance is often too large.
(8) The operation is not carried out according to the method specified in the instruction manual. The instrument itself is improperly maintained, and the instrument is used to bring sickness or overdetection.
This article by the DC resistance tester manufacturer - Shanghai 100 Test Electric Technology Co., Ltd. to provide you!
Second, avoid the method
(1) When testing gas stations and liquefied gas stations and high-rise building grounding resistance and electrostatic grounding resistance, the arrangement of buried metal (oil, gas) pipes and grounding devices and metal devices is not correct on the map Marked, therefore, the detection direction and distance of the detection table rod when detecting the grounding resistance have a great influence on the measured value. Usually the value is different with the direction and distance, and sometimes the measurement value may even be negative. In particular, the detection of buried pipeline facilities such as gas stations will often occur. The solution is: to understand the layout of the underground metal pipeline before the test, not only to view the grounding device map, but also to view the layout of other underground metal pipelines, choose to place the P, C grounding pole as small as possible.
(2) Where there is a disconnected card in the ground lead wire, disconnect the test as much as possible to avoid the impact of other devices on the test.
(3) When abnormality occurs during detection, the cause should be ascertained, or detected and compared at different times and in different directions and locations to obtain the correct detection value.
(4) In order to avoid electromagnetic interference on the leads under high electromagnetic fields, the detection leads should be relatively shortened, and the qualified inner diameter of the leads should be used as multi-strand metal wires.
(5) When detecting the grounding resistance in the place where the high-resistivity sandstone cushion is used, the P and C ground electrodes should be placed in a place where the moisture and the ground conduct well, so that the measured grounding resistance is relatively correct.
(6) Testing should be performed in accordance with the operating procedures. The testing equipment should be maintained frequently and regularly, and no super-inspection equipment should be used.

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