Reasons for the excessive no-load current of the variable-frequency speed-regulating motor

Update:19 Oct 2021

Five reasons for the excessive no-load current of the variable frequency speed control motor

1. Large air gap of variable frequency speed control motor: The main reason is: because the rotor of the motor rotates in a ventilated atmosphere containing inevitable impurities for a long time, it suffers from the abrasion of impurities and dust in the atmosphere and increases the air gap, such as those operating in metallurgical enterprises. The open-type motor has been operated for more than ten years, and the air gap has increased by about 15%. When the frequency conversion speed control motor sweeps the bore or the iron core is eccentric, the rotor is turned during maintenance, and the negative air gap is increased.

2. Increased iron core loss: During repair, because the notches are uneven and affect the wire embedding, the large notches are filed with a rough file to short-circuit the notch iron core punching piece, and the size of the notch increases, which increases the effective air gap of the motor. The iron core is corroded and rusted in a wet condition for a long time. When the motor was dismantled the windings, an open flame was used to burn the iron core and other incorrect methods, so that the insulation of the iron core punching piece was corroded, and the punching pieces were short-circuited. The rotor core is not aligned with the stator core, and the rotor core may be reversed. The iron core is severely fanned.

3. The number of winding turns is eliminated or the coil pitch becomes smaller: the elimination of the number of coil turns increases the magnetic flux density, and the core loss is proportional to the square of the magnetic flux density, resulting in a substantial increase in iron loss. The smaller the coil pitch, the lower the short-distance coefficient of the winding, and the elimination of the effective number of turns of the motor, which results in an increase in iron loss and an increase in no-load current.

4. Incorrect wiring of the variable-frequency speed-regulating motor windings: For example, 1Y connection is mistakenly connected to 1Δ connection, 1 way is mistakenly connected to 2 way, etc. 1Y connection is wrongly connected to 1Δ connection, which is equivalent to a reduction of √3 times the number of turns per phase; 1 way is mistakenly connected to 2, and the number of turns of each phase winding is reduced by 50%, resulting in a significant increase in no-load current.

5. If the rotor of the motor is not installed, the positive and negative air gap is uneven, and the shaft may be bent, the bearing may be obstructed, etc., which will increase the no-load current. As the no-load current increases, the power factor of the motor is reduced. When the rated voltage UN and rated current IN of the motor are kept stable, the output power of the motor will drop due to the low power factor. If the motor is running under the rated load, then the electric timing will have a fever due to excessive current.

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