The insulation resistance tester under UHV power can help many power workers conduct various power tests more conveniently.

The factors that affect insulation resistance are as follows:

1、 The influence of temperature

The temperature of the operating power equipment changes with the surrounding environment, and its insulation resistance also changes with the temperature. Generally speaking, insulation resistance decreases with increasing temperature. The reason is that when the temperature rises, the movement of ions and molecules inside the insulation medium increases, and the moisture and impurities, salts, and other substances in the insulation also show a diffusion trend, thereby increasing the conductivity. And reduce the insulation resistance. This is different from the variation of conductor resistance with temperature. The insulation resistance of different electrical equipment and electrical equipment made of different materials varies with temperature, and it is difficult for on-site testers to ensure that they are tested at completely similar temperatures. In order to compare the test results, relevant units have provided some equipment temperature conversion factors, but due to factors such as outdated equipment, dryness, and temperature measurement methods used, it is difficult to obtain accurate conversion factors. Therefore, when measuring insulation resistance in practice, it is necessary to record the test temperature (ambient temperature and device body temperature) and measure at a temperature as close as possible to avoid errors caused by temperature conversion. However, due to factors such as outdated equipment, dryness, and temperature measurement methods used, it is difficult to obtain accurate conversion factors. Therefore, when measuring insulation resistance in practice, it is necessary to record the test temperature (ambient temperature and device body temperature) and measure at a temperature as close as possible to avoid errors caused by temperature conversion. However, due to factors such as outdated equipment, dryness, and temperature measurement methods used, it is difficult to obtain accurate conversion factors. Therefore, when measuring insulation resistance in practice, it is necessary to record the test temperature (ambient temperature and device body temperature) and measure at a temperature as close as possible to avoid errors caused by temperature conversion.

2、 The influence of humidity and dirt on the surface of power equipment

The changes in humidity around power equipment and surface pollution caused by air pollution have a significant impact on insulation resistance. When the relative humidity of the air increases, a large amount of moisture will be adsorbed on the surface of the insulation material, resulting in an increase in surface conductivity and a decrease in insulation resistance. When a water film is formed on the surface of an insulator, the insulation resistance is lower. If the insulation resistance of a group of 220kV magnetic fired lightning arresters is measured after rain, it is only 2000M Ω; when shielding surface current, the insulation resistance is greater than 1000M Ω; when the surface is dry on sunny days in the afternoon, the insulation resistance is also measured at 1000M Ω. The dirt on the surface of power equipment also greatly reduces the surface resistance of the equipment, and the insulation resistance decreases significantly. According to the above two situations, it is necessary to use a shielding ring to eliminate the influence of surface leakage current or wipe and wipe the equipment surface, and measure the insulation resistance on site to obtain the true measurement value.

3、 The impact of residual charge

The residual charges left during the operation of large capacity equipment or the residual charges formed during testing that have not been fully discharged can cause the insulation resistance to be too high or too low, resulting in inaccurate measured insulation resistance. When the polarity of the remaining charge is the same as that of the megohmmeter, the measured insulation resistance will increase compared to the true value; When the polarity of the remaining charge is opposite to that of the megohmmeter, the measured insulation resistance will decrease compared to the true value. The reason is that when the polarity is the same, due to same-sex repulsion, the output charge of the megohmmeter is less; When the polarity is opposite, the megohmmeter outputs more charge to neutralize the remaining charge. In order to eliminate the influence of residual charges, the grounding must be completely discharged before measuring the insulation resistance. Repeated measurements should also be fully discharged. Large capacity equipment should be discharged for at least 5 minutes. For example, in a large capacity transformer, the first measurement of its winding insulation resistance after complete discharge is 4000M Ω, and the second measurement of the same winding (not fully discharged). Its insulation resistance is 4000M Ω.