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Working Principle of Clamp Earth Resistance Tester

time:2020/7/15   source:华天电力  reading:312 time

Working Principle of Clamp Ground Resistance Tester


1. Principle of resistance measurement


The basic principle of the clamp-on ground resistance tester for measuring ground resistance is to measure loop resistance. See below. The jaw part of the clamp meter is composed of voltage coil and current coil. The voltage coil provides an excitation signal and induces a potential E on the circuit under test. Under the action of electric potential E, current I will be generated in the measured circuit. The clamp meter measures E and I, and the measured resistance R can be obtained by the following formula.


2. Principle of current measurement


The basic principle of measuring current with a clamp-on earth resistance meter is the same as that of a current transformer. See below. The AC current I of the measured wire generates an induced current I1 through the current magnetic ring and current coil of the jaw. The clamp meter measures I1, and the measured current I can be obtained by the following formula.


Clamp Type Earth Resistance Tester.png


Application of Clamp Earth Resistance Tester in Power System


1. Measurement of grounding resistance of transmission line tower


Generally, the grounding of the transmission line towers constitutes a multi-point grounding system, and the grounding resistance of this branch can be measured by simply clamping the ground lead with a clamp meter.


2. Measurement of transformer neutral point grounding resistance


There are two cases of transformer neutral grounding: if there is repeated grounding, it forms a multi-point grounding system; if there is no repeated grounding, it is measured as a single point grounding.


During the measurement, if the clamp meter displays “L 0.01Ω”, there may be more than two ground leads connected to the same tower or transformer and connected underground. At this time, you should untie the other grounding down conductors, and keep only one grounding down conductor.


3. Application of power plant substation


The clamp meter can test the contact and connection of the circuit. With the help of a test line, the connection between the device in the station and the ground network can be measured. The grounding resistance can be measured at a single point.


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