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The difference between the test methods of insulation resistance tester and grounding resistance tester

The difference between insulation resistance tester and grounding resistance tester test method

(1) Test method of insulation resistance tester

The insulation resistance tester is to test the insulation degree between the phase, layer and neutral point of the wire and cable. The higher the test value, the better the insulation performance.

(2) Test method of grounding resistance tester

The grounding resistance tester is a device that detects whether the grounding resistance is qualified. The test method of the grounding resistance tester is to use the ground to connect the tester to the same potential, that is, the proximity of the reaction line or the down-conductor of the arrester to the ground. The value measured by the grounding resistance tester is an effective measure to ensure personal safety.

The principle difference between insulation resistance tester and grounding resistance tester

(1) Principle of insulation resistance tester

When measuring insulation resistance with an insulation resistance tester, apply a DC voltage U to the insulation. At this point, the current decays with time and eventually tends to a stable value.

The current of a general insulation resistance tester is the sum of capacitive current, absorption current and conduction current. Capacitive current Ic, which decays very fast; sink current Iaδc, decays much slower than capacitive current; on-current Inp tends to stabilize in a short time.

When testing with an insulation resistance tester, if the insulation is not wet and the surface is clean, the transient current components Ic and Iaδc will rapidly decay to zero, leaving only a small on-current Inp to pass, because the insulation resistance is inversely proportional. Proportional to the circulating current, the insulation resistance rises rapidly and stabilizes at a large value. On the contrary, if the insulation is damp, the on-current increases significantly, even faster than the initial value of the absorption current Iaδc, the transient current component is significantly reduced, the insulation resistance value is very low, and changes greatly with time.

Therefore, in the experiment of the insulation resistance tester, the water absorption rate is generally used to judge the moisture content of the insulation. When the absorption ratio is greater than 1.3, it means that the insulation is excellent. If the absorption ratio is close to 1, it indicates that the insulation is wet.

(2) Principle of grounding resistance tester

Grounding resistance tester is also called grounding resistance measuring instrument and grounding vibrator. The test principle of the grounding resistance test is to obtain the grounding resistance value "Rx" through the AC constant current "I" between the grounding electrode "E" of the measured object and the power electrode "H(C)", and find the grounding electrode "E" and the position difference "V" between the measuring electrode "S(P)".