Information about Ac Motor

1. Why does the ac motor generate shaft current?

The shaft of the motor—bearing—the current in the base circuit is called the shaft current.

Reasons for shaft current generation:

(1) Asymmetry of the magnetic field;

(2) There are harmonics in the supply current;

(3) The manufacturing and installation are not good, and the air gap is not uniform due to the eccentricity of the rotor;

(4) There is a gap between the two semicircles of the detachable stator core;

(5) The number of tiles with fan-shaped stator cores is not properly selected.

harm:

The surface of the motor bearing or the ball is eroded, and the shaped micro-holes are formed, which deteriorates the running performance of the bearing, increases the friction loss and heat, and eventually causes the bearing to burn.

prevention:

(1) Eliminate the pulsating flux and power supply harmonics (such as adding an AC reactor on the output side of the inverter);

(2) When designing the motor, the bearing housing and the base of the sliding bearing are insulated, and the outer ring and the end cover of the rolling bearing are insulated.

2. Why can't general motors be used in highland areas?

Altitude has an adverse effect on motor temperature rise, motor corona (high voltage motor) and DC motor commutation. The following three aspects should be noted:

(1) The altitude is high, the larger the motor temperature rises, the smaller the output power. However, when the temperature decreases with increasing altitude to compensate for the effect of altitude on temperature rise, the rated output power of the motor can be unchanged;

(2) Anti-corona measures should be taken when the high-voltage motor is used in the plateau;

(3) Altitude is unfavorable for DC motor commutation. Pay attention to the choice of carbon brush material.

3. Why should the motor not run at light load?

When the motor is running at light load, it will cause:

(1) The motor power factor is low;

(2) The motor is inefficient.