When the motor is tested at the factory, there will be a problem of three-phase resistance unbalance and three-phase current unbalance exceeding the standard. Next, Dalan Motor Xiaobian gives a brief introduction to the cause analysis and treatment of the three-phase current imbalance of the motor. method:
The national standard requirement for three-phase resistance unbalance is Y is less than or equal to 2%, â–³ is less than or equal to 1.5%, and the national standard for three-phase current unbalance is less than or equal to 10%.
The three-phase current unbalance fault refers to the three-phase no-load current of the asynchronous motor at the rated voltage when the three-phase power source is substantially symmetrical, and the deviation of any one phase from the average value shall not exceed 10% of the average value.
Analysis of the cause of the three-phase current imbalance fault: Only when the three-phase voltage imbalance is too large, or the motor itself is faulty, the motor will have a large three-phase current imbalance.
When three-phase AC motors are running with three-phase current imbalance, the possible causes are:
(1) The three-phase power voltage imbalance causes the three-phase current imbalance of the motor;
(2) short circuit between motor windings;
(3) Winding open circuit (or one or several branches in the winding parallel branch);
(4) The partial coils in the stator winding are reversed;
(5) The number of turns of the three-phase winding of the motor is not equal.
Disposal method of three-phase current unbalance fault: If a three-phase asynchronous motor generates a three-phase current imbalance fault due to the above reasons, the following methods can be used:
(1) When measuring the three-phase power supply voltage with a voltmeter, if it is unbalanced, the cause should be found to be excluded;
(2) For the short-circuit fault of the motor winding, firstly, it can be observed whether the end of the winding has burnt or discolored the coil due to high temperature, or smells of insulating burnt. When visual observation can not find the position of the short circuit between the turns, the short-circuit reconnaissance can be used for inspection. If there is a short circuit between the turns in the coil, the ammeter reading connected in series with the short circuit reactor coil circuit will increase significantly;
(3) The open circuit fault of the winding can be checked by measuring the three-phase resistance with a multimeter or a bridge meter. The maximum difference of the three-phase resistance of the motor winding must not exceed 3% of the average value of the three-phase resistance;
(4) Check the coil winding part of the stator winding to reverse the fault. A low-voltage DC voltage can be applied to the phase winding, and the polarity is checked by the slot along the slot of the core. If the indication direction of the compass on each pole group is changed by N, S, N, S in turn, it means that the winding is connected correctly; otherwise, it means that a pole group is reversed; if the compass is placed in the same pole The direction of the adjacent groove surface of the group is variable, which means that there may be individual coils embedded or wrong in the pole phase group. The pole phase group and the coil of the wrong connection or the reverse phase shall be corrected according to the connection diagram of the winding or the schematic diagram of the wiring schematic diagram;
(5) For faults in which the number of turns of the three-phase winding is not equal, the first and last ends of each phase can be energized in series, and the voltage drop is measured by the voltmeter. First, measure whether the voltage of each phase is equal, and then measure whether the voltages of the pole phases of the one phase are equal. Finally, measure whether the voltages of the coils in the abnormal pole group are equal, so that the coil with the wrong number of turns can be finally found.
----- Editor-in-Chief: Dalan Oil Pump Motor 02-Procurement Consultant
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