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Principle of Clamp Earth Resistance Tester

time:2020/7/17   source:华天电力  reading:311 time

The clamp-shaped grounding resistance tester is a major breakthrough in traditional grounding resistance measurement technology, and is widely used in the grounding resistance measurement of electric power, telecommunications, meteorology, oil fields, construction and industrial electrical equipment.


When measuring the grounding system with loop, the clamp-on grounding resistance tester does not need to disconnect the ground lead and auxiliary electrode, which is safe, fast and easy to use.


The clamp ground resistance tester can measure the ground fault that cannot be measured by the traditional method, and can be applied to the occasion that the traditional method cannot measure, because the clamp ground resistance tester measures the combined value of the resistance of the ground body and the resistance of the ground lead.


Clamp Type Earth Resistance Tester.png


Working Principle of Clamp Ground Resistance Tester


1. Principle of resistance measurement


The basic principle of the clamp-on grounding resistance tester for measuring grounding resistance is to measure the 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.


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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