Motor related Questions (Part 2)

1.what are the reasons for the motor three-phase current imbalance?

(1) three-phase voltage unbalance;
(2) a phase branch inside the motor is poorly welded or in bad contact;
(3) motor winding turn to turn short circuit or to the ground, phase to phase short circuit;
(4) Wiring errors.

2. Why can't the 50Hz motor be connected to the 60Hz power supply?

When the motor is designed, the silicon steel sheet is generally working in the saturation area of the magnetization curve. When the power supply voltage is certain, the reduction of frequency will increase the magnetic flux and the excitation current, resulting in the increase of the motor current and the increase of copper consumption, and eventually lead to the increase of the motor temperature. In serious cases, the motor may be burned due to overheating of the coil.

3. What are the reasons for the motor missing phase?

Power supply:
(1) poor switch contact;
(2) The transformer or line is broken;
(3) The insurance fuse is broken.

Motor:
(1) The screw of the motor junction box is loose and in poor contact;
(2) Poor internal wiring welding;
(3) The motor winding is broken.

4. What are the causes of abnormal vibration and sound of the motor?

Mechanical aspects:
(1) poor bearing lubrication, bearing wear;
(2) Fastening screws loose;
(3) There is debris in the motor.

Electromagnetic aspects:

(1) Motor overload operation;
(2) three-phase current unbalance;
(3) lack of phase;
(4) Short-circuit fault occurs in stator and rotor windings;
(5) The welded part of the cage rotor is broken by opening welding.

5. What do you need to do before starting the motor?
(1) Measuring insulation resistance (for low-voltage motors should not be lower than 0.5MΩ);
(2) Measure the power supply voltage. Check whether the motor wiring is correct and the power supply voltage meets the requirements;
(3) Check whether the starting equipment is good;
(4) Check whether the fuse is suitable;
(5) Check whether the motor is grounded and zero is good;
(6) Check whether the transmission device is defective;
(7) Check whether the motor environment is suitable, remove flammable products and other debris.

6. What are the causes of overheating of motor bearings?
The motor itself:
(1) The inner and outer rings of the bearing are too tight;
(2) There are problems with the shape and position tolerance of the parts, such as the coaxiality of the frame, end cover, shaft and other parts is not good;
(3) improper bearing selection;
(4) poor bearing lubrication or bearing cleaning is not clean, there is debris in the grease;
(5) Shaft current.

Aspects of use:

(1) The unit is improperly installed, such as the axial coaxiality of the motor shaft and the device being dragged is not required;
(2) The belt pulley is pulled too tightly;
(3) bearing maintenance is not good, insufficient grease or more than the use period, dry deterioration.

7. What are the reasons for low motor insulation resistance?

(1) The winding is damp or there is water intrusion;
(2) Accumulation of dust or oil on the winding;
(3) insulation aging;
(4) Motor lead or terminal board insulation damage.

Source: Power Partners