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Difference in insulation and ground resistance

time:2020/12/6   source:华天电力  reading:231 time

The difference between insulation resistance and ground resistance:


Insulation resistance is to test the degree of insulation between phases, layers and neutral points of wires and cables. The higher the test value, the better the insulation function. The insulation resistance can be measured with an insulation resistance measuring instrument.


Grounding resistance is a method of connecting electrical equipment to the same potential by relying on the earth. It is the closeness of the reaction wire or the lightning protection down conductor to the ground. The ground resistance value is a useful method to ensure personal safety. The ground resistance tester can be used to measure whether the ground resistance is qualified.


Insulation Resistance Tester (3).png


Principle of Insulation Resistance Test:


When measuring the insulation resistance, the DC voltage U is applied to the insulation. At this moment, there is a current that makes attenuation changes over time, and eventually tends to a stable value. Generally, this current is the sum of capacitive current, absorption current, and conduction current. Capacitance current Ic has a very fast decay speed; absorption current Iaδc, which decays much slower than capacitive current, conducts current Inp, which takes a short time. Tend to be stable.


Assuming that the insulation is not damp and the surface is clean, the transient current weight Ic and Iaδc will quickly decay to zero, and only a small conduction current Inp will pass. Since the insulation resistance is inversely proportional to the circulating current, the insulation resistance will rise quickly and be stable On the contrary, assuming that the insulation is damp, the conduction current increases significantly, even faster than the initial value of the absorption current Iaδc, the transient current component is significantly reduced, and the insulation resistance value is very low, and with time Therefore, in the insulation resistance experiment, the damp condition of the insulation is generally judged by the absorption ratio. When the absorption ratio is greater than 1.3, it indicates that the insulation is excellent. If the absorption ratio is close to 1, it indicates that the insulation is damaged. tide.


Principle of ground resistance measuring instrument:


After the constant current "I" is communicated between the "E" (ground electrode) and "H(C)" (power supply electrode) of the measured object, the ground resistance value "Rx" is obtained, and "E" (ground electrode) and "S" are found (P)" (measurement electrode) between the position difference "V".


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