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Analysis of Clamp Earth Resistance Tester

time:2020/7/7   source:华天电力  reading:281 time

Reducing the grounding resistance of the power line pole tower can improve the lightning resistance level of the line, reduce lightning damage accidents, reduce the contact voltage and step voltage near the pole tower, and prevent human and animal electric shock accidents. Therefore, the grounding resistance of the tower is an important data. All aspects of design, construction, and operation must be taken seriously, and its true value must be accurately measured and kept below the specified value. In the past, a grounding shaker was used to measure the grounding resistance. However, since a measurement line of more than 100 meters needs to be led out from the grounding grid and connected to two auxiliary ground electrodes, the workload is large, and it is often limited by terrain and environment. The position of the pole cannot meet the requirements, so it is difficult to obtain correct measurement results.


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Principle of Clamp Earth Resistance Tester


The clamp-type grounding resistance tester is used to measure the grounding resistance of any looped system. The instrument itself can generate a power supply potential and can generate current in any looped system. Therefore, its measurement principle is simply a full circuit ohm The law, it measures the loop resistance value of this loop system.

The method of measuring the grounding resistance of the power line tower with a clamp-type grounding resistance tester is simple, and the measurement results have high reliability, but it can only be used on high-voltage lines with overhead ground lines. Only one ground lead is allowed to be measured during the measurement. If the ground net of each tower foot is not connected, the ground lead wires of the remaining feet should be disassembled and connected with the lead wires of the measuring feet with a temporary wire (the connection point is below the clamp meter). Through the analysis of the measurement results, it can be judged whether the ground network of each tower foot is connected, and whether there is a hidden danger of poor contact of the ground lead.


Attention to the use of clamp-type grounding resistance tester


1) Whether it is tripped by the traditional voltage and current method (that is, whether the ground body under test is separated from the grounding system). If it is not tripped, the measured grounding resistance value is the parallel value of the grounding resistances of all grounding bodies.


It is probably meaningless to measure the parallel value of the grounding resistance of all grounding bodies. Because the purpose of measuring the grounding resistance is to compare it with an allowable value stipulated in the relevant standards to determine whether the grounding resistance is qualified.


2) The grounding resistance value measured with the ETCR2000 series clamp meter is the comprehensive resistance of the grounding branch. It includes the contact resistance, lead resistance and grounding body resistance of the branch to the common ground wire. Under the condition of tripping with the traditional voltage and current method, the measured value is only the resistance of the grounding body.


The error of the clamp ground resistance tester


(1) The error S1 introduced by the standard ammeter: Since the highest accuracy of the detected current is 0.5%, it is sufficient to select the 0.1-level standard ammeter.


(2) The error S2 brought by the standard voltmeter: Because the accuracy of the meter under test is not high, the use of a 0.05-level standard voltmeter can meet the requirements. Considering that the measured voltage is small, its measurement error generally does not exceed ±0.5%.


(3) Error caused by the input impedance of the standard voltmeter S3: Because the measured resistance is less than 1Ω, the error caused by the input impedance of the standard voltmeter is relatively negligible.


(4) The error S4 introduced by the resistance: detected by this method, the connected resistance is not used as a standard, but only as a carrier for the measurement of the tested table and the standard table, so the accuracy of the resistance does not affect the measurement result and affects the measurement result The main factor is the stability of the resistor. Due to the large current requirements of the connected resistor, this resistor is usually made of special materials and processes. There are certain requirements for its stability, plus the inspected table and the standard table are almost Simultaneous measurement, so errors introduced by resistance stability are negligible


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