By hvhipot 
1、 Why is the megohmmeter most widely used in insulation testing of high-voltage electrical equipment?
The magnitude of insulation resistance value can effectively reflect the overall moisture, pollution, severe overheating and aging defects of insulation. Moreover, using a megohmmeter to measure insulation resistance is simple, safe, conceptually clear, and inexpensive. Therefore, megohmmeters are widely used in insulation testing of high-voltage electrical equipment.
However, when testing insulation with a megohmmeter, there are the following obvious drawbacks:
(1) The voltage of a typical DC megohmmeter is below 2.5KV, which is much lower than the operating voltage of some electrical equipment. When there are certain defects in the equipment, the leakage current under high voltage is much larger than that under low voltage, that is, the insulation resistance under high voltage is much smaller than that under low voltage.
(2) The output current of a typical DC megohmmeter is below 2mA. When the equivalent capacitance of the tested equipment is large (such as power transformers or generators), the charging speed is slow and it is difficult to obtain accurate data.
2、 What is the effect of temperature on insulation resistance value? How to equate the insulation resistance values of the same test sample under different temperature environments?
The BC2000 high-voltage insulation tester has a built-in CPU that can automatically convert the insulation resistance to the standard temperature value based on different environmental temperatures.
Attachment: Temperature Conversion Factor Table for Insulation Resistance of Oil immersed Transformers
Temperature difference (0C) 5 10 15 20 25 30 35 40 45 50 55 60
Conversion factor 1.2 1.5 1.8 2.3 2.8 3.4 4.1 5.1 6.2 7.5 9.2 11.2
3、 Why do some electrical equipment need to test insulation resistance and polarization curve?
Measuring insulation resistance is one of the simplest and most commonly used methods to understand the insulation of electrical equipment. The measurement of absorption ratio and polarization index can accurately reflect the insulation condition of large capacity samples, but the polarization curve is the curve of the relative value of insulation resistance over time, which can more accurately reflect the insulation condition of the sample. Therefore, for some large capacity samples, insulation resistance and polarization curve need to be tested.