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Factors influencing insulation resistance tester

time:2020/10/19   source:华天电力  reading:247 time

Electricity workers at work, often need to use insulation resistance tester, the device's main function is to test the transformer, generator, transformer, high voltage motor, electric power capacitor, power cable, lightning arrester, such as insulation resistance, is easy to use, high accuracy, etc, but many people at the time of first use, sometimes difficult to achieve the instrument test results, the factors affected the accuracy of insulation resistance tester to test what?

Generally, the resistance of the material decreases with the increase of temperature and humidity in the environment. Compared with enterprises, surface resistivity is more important and sensitive to environmental and humidity data, while volume resistivity is more sensitive to temperature changes. Humidity can increase, surface information leakage increases, and the volume conductance current also increases. As the temperature keeps rising, the motion development rate of carrier speeds up, and the absorption current and conductance current of different materials in the medium will increase correspondingly. According to relevant research and literature reports, the resistance value of general working medium at 70C is only 10% of that at 20C. Therefore, when measuring the resistance of the technical material, it must be indicated that the sample and the environment can reach an equilibrium temperature and humidity.

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The resistance (rate) value of a dielectric material cannot be kept constant over a wide voltage range, that is, Ohm's law does not apply. At room temperature, the conductance current increases linearly with the applied voltage in the lower voltage range, and the resistance value of the material remains unchanged. After exceeding a certain voltage, the conductance current increases much faster than the test voltage, and the resistance of the material decreases rapidly. It can be seen that the higher the applied test voltage is, the lower the resistance value of the material is. Therefore, the resistance value of the material tested under different voltages may be quite different.

It is worth noting that the change in the resistivity of the material determines the result of the electric field strength in the test rather than the test voltage. If the test electrode distances are different for the same test voltage, the test results for the resistivity of the material will be different, and the smaller the distance between the positive and negative electrodes, the smaller the test value.

When the measured pressure is in relation to the DC voltage of a material, the current to the tested material is an instantaneous value that is not stable, but has a decay process. When pressurized, a large charging current flows through, followed by a slow decrease in the relatively long absorption current, and finally a relatively stable conduction current. Higher measured resistance takes longer to reach equilibrium. Thus, the measured resistance value, when read correctly, is read after a steady or pressure reading taken 1 minute later.

In addition, the resistance value of high insulation structure material is also related to its electrification history. In order to accurately analyze and evaluate the electrostatic performance of the materials, when a resistance (rate) test can be performed on the building materials, it should first be de-electrification treatment, and stand for a certain time, which can be taken for 5 minutes. Then, the test should be designed according to the measurement system program. Generally speaking, for the test of a kind of learning material, at least 3 ~ 5 samples should be randomly selected for management test, and their average value should be taken as the main test results.

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