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Measuring principle of ground tester

time:2020/5/6   source:华天电力  reading:314 time

What is a ground resistance tester?


The resistance between the ground electrode and the ground is often referred to as the ground resistance. To be more precise, the ground resistance is the resistance of the ground conductor, the contact resistance between the ground conductor and the earth, and the resistance of the earth. Ground resistance differs from ordinary resistors in that it has the following special characteristics:


Earth Resistance Tester.png


• polarization


Because the earth behaves like an electrolyte, it is polarized, so the dc current creates an electromotive force in the opposite direction, making it impossible to measure accurately. Therefore, the ground resistance is usually measured by square or sine waves of frequencies ranging from tens of Hertz to 1 kHz.


• special measurement Settings


Ground resistance is the resistance between the ground electrode and the ground. Measurements cannot be made without electrodes being inserted into the ground. Because the earth's resistivity is low, there is a voltage drop near the electrode from which the current used to make the measurements flows. Therefore, in order to accurately measure the resistance of each grounding electrode (E electrode, S [P] electrode and H [C] electrode), it is necessary to remove about 10 m.


• presence of interference


The measurement of ground resistance can be affected by interference, such as ground potential and auxiliary ground electrode. The ground potential caused by the leakage current of the equipment connected to the ground electrode is superimposed on the signal detected by the ground resistance tester, thus affecting the measured value. In addition, if the grounding resistance of the auxiliary grounding electrode is high, the measurement current will be reduced, making the measurement more susceptible to noise such as the grounding potential.


Measuring principle of ground resistance tester


An ac supply voltage is applied between the H (C) and E electrodes, resulting in the measurement of the ac current I flowing through the ammeter. In addition, an ac voltmeter is used to measure the voltage V generated between the S (P) electrode and the E electrode during the flow of current I.


Then, the grounding resistance RX of electrode E is calculated according to the measured current I and voltage V. It is impossible to precisely measure the voltage between electrodes H (C) and E, or H (C) and S (P) electrodes.


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