The insulation resistance of water pump motors is usually measured with a 500V megger (insulation resistance tester). It can measure insulation resistance between phases and between phases and earth. There are instructions for use on the cover of the megger.
The use and precautions of the megger are as follows:
1. Before measurement, the power supply to the equipment under test must be turned off and the device must be short-circuited. and thrown to the ground. Never allow the equipment to be powered for measurement to ensure the safety of people and equipment. For equipment likely to induce high voltage, this possibility must be eliminated before measurements can be made.
2. The surface of the object to be measured must be clean. Reduce the contact resistance to ensure the accuracy of measurement results.
3. Before measurement, the megger must be testedt open circuit and short circuit to check if the megger is in good condition. That is, before connecting the megger to the object to be measured, shake the handle so that the generator reaches the rated speed (120 rpm) and observe whether the pointer points to the “∞” position of the scale. Short circuit the “line (L) and ground (E)” terminal, slowly shake the handle and observe whether the pointer points to the “0” position of the scale. If the pointer cannot point to the finger position, this indicates that the megger is defective and should be inspected before use.
4. When using the megger, it should be placed in a stable and solid place away from large external current conductors and external magnetic fields.
5. The wiring must be correct. There are generally three terminals on the megger, among which L is connected to the insulated conductive part between the tested object and the ground, andE is connected to the shell of the object under test or to ground. G is connected to the shield of the tested object or the part that does not need to be measured. When measuring insulation resistance, usually only the “L” and “E” terminals are used. However, when measuring the insulation resistance of the cable to ground or if the leakage current of the equipment under test is large, the “G” terminal should be used. be used and terminal “G” must be used. Complete the shield or enclosure. After the circuit is connected, you can turn the shake handle clockwise. The shaking speed should be slow to fast. When the rotation speed reaches about 120 revolutions per minute (ZC-25 type), continue to rotate at a constant speed and take a moment. reading after 1 minute. And it is necessary to take readings by shaking. Don't stop and take readings.
Note: When usingWhen using a megger to measure the insulation resistance of electrical equipment, be sure to note that the "L" and "E" terminals cannot be connected reversely. The correct connection method is: wire terminal "L" is connected to the conductor of the device under test, ground terminal "E" is connected to the grounded device shell, ground terminal shield "G" is connected to the insulated part of. the device under test. If "L" and "E" are connected reversely, the leakage current flowing through the interior and surface of the insulator will gather to earth through the shell, from earth it will flow into the measuring coil through "L", thus causing. "G" loses its shielding effect and gives the measuring tape a big error. In addition, because the insulation degree between the internal wire of the "E" end and the case is lower than the insulation degree between the "L" end and the case. When the megger is placed on the ground and usedIlized with the correct wiring method, the insulation resistance between the "E" terminal and the instrument shell and the shell to ground is equivalent to a short circuit and will not cause errors. “L” and “E” are connected in reverse, when the insulation resistance of “E” to ground is connected in parallel with the measured insulation resistance. This makes the measurement results smaller and leads to larger errors in the measurement.
6. When measuring, place the megger in a horizontal position, and when the handle is turned, the No short circuit allowed. The handle should be shaken slowly and gradually. If the pointer is at zero, it means that the measured insulation may be short-circuited. At this time, the handle cannot continue to shake to prevent the meter coil from shaking. be damaged by heat.
7. Once the reading is complete, discharge the device under test. The discharge method is to remove the fground the megohmmeter and short-circuit it with the device under test (no discharge of the megohmmeter).