How to choose the model and specifications of the megohmmeter should be based on the test voltage level. The user can select the applicable high-voltage megohmmeter according to the characteristics of the test product and the requirements of the test procedure. The output short-circuit current and range should meet the requirements of the regulation. High anti-field interference capability and dynamic measurement accuracy, convenient and safe to use, and cost-effective.

According to the requirements of the test object, the megohmmeter can be roughly divided into three types: universal type, dominant type, and type. According to the prevention and handover test procedures of power equipment, it is used as a universal megohmmeter test to measure the insulation resistance of the sample. The voltage level is 500V, 1000V.

The leading type megohmmeter mainly measures the insulation resistance of the test sample. The absorption ratio or polarization index is generally 2500V. The 5000V type megohmmeter is used to measure the insulation of the windings of synchronous generators, DC motors and AC motors. Resistance, absorption ratio and polarization index. Sometimes it is necessary to measure or calculate the true insulation resistance value. For the test product with a large capacitive load, generally select a suitable voltage level and a large enough output short-circuit current, a large range of insulation value, and a megohmmeter that automatically discharges the test product, otherwise the R15S resistance value will have a greater impact , And make the absorption ratio test result appear larger error.

For the test site with strong interference, the analog megohmmeter should be selected, because the digital display megohmmeter has large fluctuations in the measurement data, so that the real resistance value cannot be confirmed, and the analog megohmmeter itself Strong magnetic field interference is relatively slow (mechanical meter head damping effect). Even if it is affected, the indicator head display only slightly oscillates, and the range of indication is also very intuitive.

1. Electrical circuits, equipment, appliances, etc. should be tested for insulation resistance before or after installation according to the specific conditions, and the power test can only be performed after they are qualified.

2. Measure the insulation resistance. When there is no special requirement, use the voltage of the megohmmeter to wait until the level is:

(1) For electrical equipment or circuits below 100V, use a 250V megohmmeter.

(2) For electrical equipment or circuits below 500V to 100V, use a 500V high-voltage megohmmeter.

(3) For electrical equipment or circuits below 3KV to 500V, use 1000V high-voltage megohmmeter.

(4) For electrical equipment or circuits below 10KV to 3KV, use 2500V high-voltage megohmmeter.

(5) For electrical equipment or circuits of 10KV and above, use 2500V or 5000V high-voltage megohmmeter.

3. Sub-project name: fill in the sub-item according to the occurrence.

4. Instrument model: fill in the megohm meter actually used.

5. Voltage: refers to the output voltage of the megohmmeter.

6. Power distribution cabinets, screens, boxes, panels, equipment: fill in according to the construction drawing number.

7. Location: Fill in according to the installation location of the tested equipment. Road type: fill in according to the construction system drawing number.

Selection of the voltage level of the megohmmeter

The test voltage of the megohmmeter (megohmmeter) is related to the rated working voltage of the tested product, and is far lower than the tested product's working voltage.

1. According to the test voltage level, it can be divided into: low voltage: 50V, 100V, 250V, 500V, 1000V; high voltage: 2500V, 5000V, 10KV;

2. The voltage levels of megohmmeters (megohmmeters) commonly used in power equipment are: 100V, 2500V, 5000V;

3. The selection of test voltage is based on the rated working voltage and capacity of the test product, divided into:

(1) For low-voltage electrical equipment and household appliances, the selected test voltage level is often higher than the working voltage;

(2) The working voltage of power equipment is relatively high, and the test voltage level is often lower than the working voltage of the tested product. It is stipulated by insulation test regulations and corresponding standards.

When there are no special provisions in the test procedures, the following voltage levels are recommended for insulation measurement of electrical equipment or auxiliary and control circuits:

(3) It is generally stipulated that when the test voltage level is 2500V and above, the absorption ratio or polarization index of the test sample is measured;

(4) The test voltage is different, the internal dielectric relaxation polarization strength of the test product is different, and the insulation resistance value of the test product is also different.

However, the insulation resistance index is not very sensitive to small changes in test voltage.

1. For the test product with a large capacitive load, generally choose a megohmmeter that has a suitable voltage level, a large enough output short-circuit current, a large range of insulation value, and can automatically discharge the test product, otherwise the insulation resistance will be Will have a greater impact, and make the absorption ratio test results have a greater error.

2. For the test site with strong interference, the analog megohmmeter should be used, because if the digital megohmmeter is selected, the measurement data will have large fluctuations, so that the real resistance value cannot be confirmed, and the analog megohmmeter It is relatively slow to the strong magnetic field interference (mechanical meter head damping effect), even if it is affected, the pointer meter head only slightly swings, and the range of indication is also very intuitive.

3. For occasions where the interference is small and the insulation resistance value is required to be measured, a digital megohmmeter should be used, because the digital megohmmeter displays intuitively and has high accuracy.

4. For large-capacity samples such as absorption ratio and polarization index, an intelligent megohmmeter that can automatically measure absorption ratio and polarization index should be selected.