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Basic Knowledge of AC Motor
Dec 29, 2018
Three Phase AC Roller Door Opener Gate Motor

1. Why can't I start the ac motor in a cold environment at will?

The motor is too long in a low temperature environment and will:

(1) Motor insulation cracking;

(2) Bearing grease freezes;

(3) Wire joint solder powder.

Therefore, the motor should be stored in a cold environment and the windings and bearings should be inspected before operation.

2. What are the reasons for the ac motor three-phase current imbalance?

(1) Three-phase voltage imbalance;

(2) The welding of a certain phase branch inside the motor is poor or the contact is not good;

(3) Short circuit between motor windings or short circuit to ground and phase;

(4) Wiring error.

3. Why can't a 60Hz ac motor be connected to a 50Hz power supply?

When designing the motor, the silicon steel sheet is generally operated in the saturation region of the magnetization curve. When the power supply voltage is constant, lowering the frequency will increase the magnetic flux, and the excitation current will increase, resulting in an increase in the motor current, an increase in copper consumption, and eventually an increase in the temperature rise of the motor. In severe cases, the motor may be burnt due to overheating of the coil.

4. What are the reasons for the lack of phase of the ac motor?

Power supply:

(1) Poor contact in the switch;

(2) Transformer or line disconnection;

(3) The fuse is blown.


(1) The motor junction box screws are loosely connected;

(2) Poor internal wiring;

(3) The motor winding is broken.

5. What are the reasons for the low insulation resistance of the ac motor?

(1) The winding is damp or has water intrusion;

(2) accumulation of dust or oil on the windings;

(3) Insulation aging;

(4) The insulation of the motor lead or terminal block is broken.

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