The most sensitive and most prone to faults in the use of three-phase asynchronous motors is the unevenness of the three-phase current of the motor. Today, the editor of Dalan Motor analyzes the factors that may cause the unevenness of the three-phase current, and explores the production mechanism and provides a basis for test verification.
1. Distinguish between power supply problem and motor problem
In this case, the primary task is to eliminate the power factor, and the configuration defects of the power supply system switch cabinet and its components can easily lead to uneven current. Secondly, check the wiring of the motor in detail to see if it is loose or virtual.
(1) Check the power supply voltage
Use an AC voltmeter to measure and check whether the three-phase power supply voltage of the motor inlet is balanced.
(2) Check the motor wiring
The standard universal motor has 6 terminals. In the first step, check whether the cold-pressed terminals of the motor's main line or the internal winding of the motor are firmly clamped and whether the tightening nut is loose; in the second step, check the connection relationship and compression of the connecting piece; in the third step, check the external cable Whether the connector matches the terminal, and whether the compression nut is tightened.
(3) Whether the first and last ends of the stator windings of each phase or part of the coils in the stator windings are connected reversely.
(4) Whether the stator winding has inter-turn or ground fault. If there is a turn-to-turn fault, the motor winding will have different degrees of burnt smell. If the site cannot be inspected, it can only pass professional inspection and judgment.
(5) Is the number of turns of stator winding of each phase the same? Most of this problem occurs in the repair process of the motor, especially after rewinding the stator winding during the overhaul, the number of turns of each coil may be somewhat different.
(6) Whether there are individual branches of multi-channel parallel stator winding broken. This problem can be found through resistance testing. Resistance testers, DC bridges and other instruments are used at the production site, and high-precision multimeters can be used to solve the problem.
(7) There are two cases of unbalanced power supply voltage: First, the three-phase load of the power grid is unbalanced, resulting in uneven three-phase voltage; Second, the no-load is normal, and the three-phase voltage is uneven after the motor is loaded. Usually there is a defect in a link of the power distribution system, such as the ablation of the main contactor of the switchgear, the connection of the main line is not securely fastened, etc.
----- Responsible Editor: Dalan Oil Pump Motor 02-Procurement Consultant
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