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(1) The insulation resistance of newly installed insulators should be greater than or equal to 500M Ω.

(2) The insulation resistance of insulators during operation should be greater than or equal to 300M Ω.

(1) Temperature has a significant impact on insulation resistance, which decreases with increasing temperature. The reason is that the temperature increases, the polarization of the insulation medium intensifies, and the increase in conductivity leads to a decrease in insulation resistance. The reason for the change is related to the degree of temperature change and the properties and structure of the insulation material.

(2) Humidity has a significant impact on surface leakage current, as it adsorbs moisture on the insulation surface, forming a water film that significantly reduces insulation resistance.

(3) Degradation caused by mechanical overload of insulators.

(4) Deterioration of moisture absorption of porcelain parts.

(5) Deterioration of internal and external stress overlap in porcelain components.

(6) Deterioration caused by thermal expansion of porcelain insulators.

(7) Deterioration of saturated expansion of steel cap pouring cement.

(8) Deterioration of freezing and expansion properties of steel cap pouring cement.

(9) Deterioration of electrical corrosion of steel caps and feet.

(10) Deterioration caused by overvoltage of insulators.

(11) Deterioration caused by internal defects in insulators.

For single component insulators, the insulation resistance can only be measured in the event of a power outage. According to relevant regulations, a 2500V and above megohmmeter is used. The commonly used ones are 2500V and 5000V megohmmeters, as well as specialized instruments with higher voltages. But in fact, within 1 * 104M Ω, insulation resistance measured by 2500V and 5000V megohmmeters with the same accuracy at the same humidity is basically the same. When the measured insulation resistance is greater than 1 * 104M Ω, the 2500V megohmmeter cannot read the accurate insulation resistance value and can only count it as ∞. A 5000 megohmmeter can achieve a maximum insulation resistance of 2 * 105M Ω.

For insulators with multiple component combinations, the insulation resistance can be measured with power off or live. The method is to connect a high resistance to a live insulator, so that the megohmmeter for measuring insulation resistance is at ground potential, and subtract the high resistance value from the measured insulation resistance to obtain the insulation resistance value of the tested insulator. The principle wiring for measuring the insulation resistance of insulators with electricity, where R is the resistance in the high resistance pole, with a resistance value of 10-20k Ω/V and a length of 0.5-105kV/cm, and a unit resistance capacity of 1-2W; C is the grounding capacitance, which can keep the megohmmeter at ground potential. The insulation resistance of C should reach the maximum limit of the megohmmeter to ensure measurement accuracy. The capacitance of C ranges from 0.01 to 0.05 μ F. It should be able to withstand DC voltage above 3000V.