1. Insulation resistance is the most basic insulation indicator for electrical equipment and electrical circuits. For the test of the connection of low-voltage electrical devices, the insulation resistance of the motor, power distribution equipment and distribution lines at normal temperature should not be lower than 0.5M (for the equipment and lines in operation, the insulation resistance should not be lower than 1M/kV).
2. The insulation resistance of low-voltage electrical appliances and their connecting cables and secondary circuits should not be lower than 1M; in humid environment, the insulation resistance should not be lower than 0.5M; the insulation resistance of small-circuit small busbars should not be lower than 10M. The insulation resistance of Class I handheld power tools should not be less than 2M.
Generally, the insulation resistance value of the motor is measured by a megohmmeter, and the insulation resistance value between each two-phase winding and each phase winding and the casing is measured to judge whether the insulation performance of the motor is good or bad.
When measuring the insulation resistance using a megger, the motor is usually measured with a 500 volt megger for a motor below 500 volts and a 1000 volt megohm for a motor with a voltage of 500 to 1000 volts. Motors with voltages above 1000 volts were measured with a 2500 volt megger.
When the motor is in a hot state (75 ° C), the insulation resistance of a small and medium-sized low-voltage motor is generally not less than 0.
5 megohms, the insulation resistance value of the stator of the high-voltage motor per kilovolt working voltage should be not less than 1 megohm, and the insulation resistance value of the wound rotor winding per kilovolt working voltage should be at least 0.
5 megohms; the insulation resistance of the secondary circuit of the motor should not be less than 1 megohm.
The motor insulation resistance measurement steps are as follows:
(1) Disassemble the joints of the 6 ends of the motor junction box.
(2) Put the megohms flat, do not wire, shake the megohmmeter. The hands should be pointed, and then the two terminals with (line) and (ground) on the watch should be shorted with the test clip with the line, and the handle should be shaken slowly, and the hand should be pointed.
(3) Measure the resistance between the three-phase windings of the motor. Connect the two test clips to any end of any two-phase winding, put the table flat, shake the megohmmeter at a constant speed of 120 rpm for one minute, and read the indication value of the stable needle.
(4) In the same way, measure the insulation resistance of each phase around the phase and the casing. However, it should be noted that the terminal marked or grounded on the watch should be connected to the enclosure without insulation.
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