# Power detection technology / Power detection

## Detection Technology

### Three test methods of ground resistance tester

The ground resistance tester should be used in the ground resistance test. During use, not only the method steps used, but also the correct and appropriate instrument should be selected. There are only three types of measurement methods: ground pile method, clamp method, combined ground pile and clamp method. The following is an introduction to these three types of methods for correctly selecting grounding resistance testers.

Ground pile method:

The pile method can be divided into two-line method, three-line method and four-line method. 1. Two-wire method: This is the initial measurement method: connect one wire to the ground under test and the other to the auxiliary ground electrode. The measurement result of this method is R=ground resistance + ground pile resistance + lead and contact resistance , So the error is large, it is generally not used now; 2. Three-wire method: This is an improved type of the two-wire method, that is, two auxiliary ground poles are used and calculated by formulas. When the middle auxiliary ground electrode is 0.62 times the total length, the error caused by the resistance of the ground pile can be basically eliminated. This method is still in use, but this method still cannot eliminate the contact resistance caused by the weathering and corrosion of the grounding body under test. 3. Four-wire method: This is an improved method based on the three-wire method. This method can eliminate errors caused by auxiliary grounding resistance, test leads and contact resistance.

Clamping method:

The clamp method is divided into single clamp method and double clamp method. 1. Double clamp method: using the principle that a conductor in a changing magnetic field generates an induced voltage, a pliers is used to pass a changing current to generate an alternating magnetic field. The magnetic field makes the conductor within it generate a certain induced voltage. The other clamp measures the induced current generated by the voltage, and finally uses Ohm's law to calculate the loop circuit value. The applicable conditions are that a loop is formed, and the other end resistance is negligible; 2. Single clamp method: Single clamp method The essence is to make the two pliers of the double pliers method into one body. However, if mechanical damage occurs, the two adjacent pliers will inevitably interfere with each other, which will affect the measurement accuracy.

Combination method of pile and clamp:

This method is also called the selective electrode method. The measurement principle of this method is the same as the four-wire method. Because when using Ohm's law to calculate the result, its current value is measured by an external current clamp. It is not measured by the internal circuit like the four-wire method, which greatly increases the scope of measurement, especially to solve the problem of multi-point grounding of power transmission towers and metal connections underground.

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