Low-voltage motor insulation resistance qualified standards are: for general use of the motor, whether three-phase or single-phase motor insulation resistance as long as greater than 0.4-0.5 megohm even qualified. According to another statement, low-voltage motor insulation resistance to ground should reach more than 2 megohms.
It should be noted that the insulation resistance of the motor is the greater the better, but too high a resistance value may lead to aging and deterioration of the insulation material, affecting the service life of the motor.
A reasonable range of insulation resistance to ground for low voltage motors should be between 2 megohms and 100 megohms. 1 megohm = 1,000,000 ohms. That is to say, every 1 volt voltage 1000 ohm resistance or more for insulation qualified standards. For the handover test of low-voltage electrical installations, the insulation resistance of motors, distribution equipment and distribution lines at room temperature should not be less than 0.5MΩ (for equipment and lines in operation, the insulation resistance should not be less than 1MΩ/kV).
The insulation resistance of low-voltage appliances, their connecting cables and secondary circuits should not be less than 1MΩ in general; in the humid environment should not be less than 0.5MΩ; the insulation resistance of the secondary circuit of the small busbar should not be less than 10MΩ.The insulation resistance of class I hand-held power tools should not be less than 2MΩ.
Motor insulation resistance measurement steps are as follows.
(1) Disassemble the coupling tabs of the 6 ends in the motor junction box. (2) Remove the six terminals in the motor junction box.
(2) put megohm flat, not wired first, shaking megohm meter. The needle should point to ‘∞’, and then the table with ‘1’ (line) and ‘e’ (ground) of the two terminals with the line of the test clip short, slowly shake the handle, the needle should point to the ‘0’.
(3) Measure the resistance between the three-phase windings of the motor. The two test clips were connected to any two-phase winding of any one end, flat rocking table.
Selection of shaking table voltage level should be noted that the measurement of insulation resistance of low-voltage electrical equipment below 500V, with a rated voltage of 500V shaking table.
Before measurement, the rocking meter should be tested for open circuit and short circuit to check whether the meter is good or not. When the test will be the first two connecting lines open circuit, shake the handle, the pointer should be pointed at the ‘∞’ position, and then the two connecting lines short-circuited, gently shake the handle, the pointer should be pointed at the ‘0’, or else the shaking table has a fault, need to overhaul.
The surface of the measured object should be clean and dry to reduce the error. Before measurement, the power supply must be cut off and the measured equipment must be fully discharged to prevent personal and equipment accidents as well as to get accurate measurement results.
Measurement, should be put on the rocking table smooth. l end connected to the measured object, E end grounding, rocking handle speed should be gradually accelerated from slow, and keep the speed at 120r/min or so. If the measured equipment is short-circuited, the pointer swings to the ‘0’ point should immediately stop shaking the handle, so as not to burn the instrument.
Reading time to shake the expression to a certain speed for one minute after reading the measurement results shall prevail.
Motor insulation resistance, as long as each kilovolt is greater than 1 megohm even if qualified.
For general use of the motor, whether three-phase or single-phase motor insulation resistance as long as greater than 0.4 - - 0.5 megohm even qualified. Of course, the insulation resistance of the motor is the greater the better.
The insulation resistance of the motor is: winding and winding between (that is, often referred to as phase to phase), winding and shell between (that is, often referred to as phase to ground) resistance. For the general motor can be used 500V shaking table test, according to the specification: low-voltage electrical equipment or line between the phase, phase-to-ground insulation resistance should be greater than 0.5 megohm. Therefore, the insulation resistance of the motor winding to the shell 5 megohm is qualified.
