The comprehensive inspection and maintenance of the motor not only includes the routine motor cleaning, the measurement of tolerance , the replacement of bearings, the inspection of leads, but also includes some test items. Below I make a simple summary of the general test items of the motor.
The inspection test items of three-phase asynchronous motor include: insulation resistance measurement, winding dc resistance measurement, voltage withstand test and no-load test, etc.
1. Measurement of insulation resistance:
Measuring the insulation resistance between each phase winding and each phase winding on the housing is the most convenient and non-destructive inspection of insulation.Though these inspection, it detect whether the winding insulation is seriously affected by moisture or has serious defects.The following defects can also be found effectively: the overall insulation quality is poor;Insulation become damp;There are penetrating conductive channels between the poles;Poor insulation surface condition.The following defects cannot be found by measuring the insulation resistance: local defects in the insulation, such as non-penetrating local damage, bubbles, delamination, etc.
In the inspection test, only the cold insulation resistance of the stator winding before the motor runs is measured, including the insulation resistance between the winding phases and the insulation resistance of each phase winding to the housing (ground).For a wound motor, the insulation resistance of the rotor winding needs to be measured.
The measurement method usually use hand-type megohm meter. For low-voltage motor, 500V megohm meter is used for measurement, while for high-voltage motor, 1000V megohm meter and 2500V megohm meter are used for measurement.Measuring insulation resistance before need to dismantle the motor wiring outside, in the process of the measuring speed of megger must maintain basic constant (120 r/min), after shake the megger for a minute,read out the pointer indicating values.For low voltage motor , insulation resistance should not be less than 0.5 M Ω, and for the motor which had replaced winding should be not less than 5 M Ω.For high voltage motor, should be not less than 1 m Ω/kV.
For large motors, the insulation resistance can be measured to determine whether the winding is damp, and its absorption ratio coefficient R60/R15 should be no less than 1.3, where R60 and R15 are the insulation resistance values read out when the meohmeter shakes 60s and 15s respectively.
The absorption ratio K=R60/R15, K always is more than 1 and the larger the absorption ratio is, the more significant the absorption phenomenon is and the better the insulation performance is. The absorption ratio is the ratio of insulation resistance of the same sample at two different times, excluding the influence of insulation structure and volume size.Generally, absorption ratio K≥1.3 is taken as the standard for good insulation condition of equipment. In order to accurately judge, insulation resistance R and absorption ratio K should be considered simultaneously. Only when both meet the requirements, can the insulation of equipment be considered good.
Other inspection refer to the followed articles.
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