Generator bearing insulation measurement method:
1. Bearing seat insulation: Use a measuring point of the megger to face the seat of the bearing and the other measuring point to face the bearing seat. Ground (mainly to check whether the insulating plate at the bottom of the bearing seat and the insulating sleeve of the anchor bolt are installed correctly or damaged).
2. Bushing insulation: use one measuring point of the megger to face the bearing seat, and the other measuring point to face the bushing (mainly to check the insulation between the shell and the bearing seat). If the insulation board is installed correctly or is damaged).
3. Note: Since the lubricating oil used in some units has an insulating effect, there is no insulating plate between the bearing and the seat of the bearing during the installation processwe. It is impossible to measure the insulation of the above two types without starting the oil pump and cranking the oil. Once the insulation is measured after startup, the insulation will be qualified.
How to shake the insulation of the water pump motor?
The instrument used to measure the insulation resistance of electrical equipment is called a “megger”. The traditional megger is usually a megger. used By crank, the megger generator rotates to generate voltage, which is converted into high voltage direct current by the circuit and applied to the equipment, thereby reading the insulation resistance value of the electrical equipment. Hence, the megger. is commonly called “megger”. The name comes from the way it works.
“Telemetry” is a concept in electrical system automation, meaning long distance measurement. Generally, the quantities measured include: the tension, current, line voltage, zero sequence current, power, power factor, etc. , but rarely used for insulation resistance measurements.
In summary, insulation measurement should be carried out by “shake measurement”.
When you use a megger to measure insulation resistance, why do you need to read the value while shaking it
To measure insulation resistance insulation of water pump motors, a 500 V megger is generally used (insulation resistance test surface). 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 leave the equipmentbe 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 should be subjected to open circuit and short circuit test to check whether 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, it indicates that the megohmbe 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, and E is connected to the shell of the tested object or the 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. Once the circuit is connected, vYou 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 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 backwards, the leakage current flowing through the interior and surface ofthe insulator will gather towards earth through the hull, 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 used 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 of 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. Place the megger in a horizontal position during shaking measurement and do not allowno short circuit between terminal buttons when handle is turned. 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 involves removing the ground lead from the megger and shorting it to the device under test (no discharging the megger).
As the megger is a generator, there are 500 V, 1000 V, 2500 V and 5000 V meggers. The 5000 V megger requires no less than 120 rpm per minute . Only when the rotation speed is sufficient can it achieve tension. level to be precise. Therefore, the value read by shaking is accurate. This statement “so that the value read by shakingbe precise” is not accurate. The insulation resistance curve of the high voltage measurement should first fall, then increase, and last for 2 minutes. The low voltage measurement insulation resistance curve is relatively stable and lasts 2 minutes.