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English
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2022
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09
What factors affect the change of insulation resistance
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【Summary】Influence of temperature: temperature has a great influence on insulation resistance. Generally, insulation resistance decreases with the rise of temperature.
1. Effect of temperature: temperature has a great impact on insulation resistance. Generally, insulation resistance decreases with the rise of temperature. The reason is that when the temperature rises, the polarization in the insulating medium intensifies, which increases the conductivity and reduces the insulation resistance. It is also related to the degree of temperature change and the nature and structure of insulating materials. Therefore, the temperature must be recorded during measurement so that it can be converted to the same temperature for comparison.
2. Influence of humidity: the insulation surface absorbs moisture, which forms a water film on the surface of the porcelain bushing, often significantly reducing the insulation resistance. When the relative humidity in the air is high, it will absorb more moisture, which increases the conductivity, and also reduces the insulation resistance value.
3. Effect of discharge time: after each insulation measurement, the tested shall be fully discharged, and the discharge time shall be longer than the charging time, so as to drain the remaining charge. Otherwise, during the re-measurement, due to the influence of the charge, its charging current and absorption current will be smaller than the first measurement, resulting in the false phenomenon that the absorption specific insulation resistance value increases, which often occurs when testing cables.
4. Analysis and judgment: insulation of high-voltage electrical equipment with large capacitance, such as cables, transformers, generators, capacitors, etc. It is mainly based on the absorption ratio. If the absorption ratio is significantly reduced, it means that the insulation is affected by moisture or the oil quality is seriously degraded.
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