1. Why does the AC Washer Motor generate shaft current? […]
1. Why does the AC Washer 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.
The surface of the AC 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.
(1) Eliminate the pulsating magnetic flux and power supply harmonics (such as adding an AC reactor on the output side of the inverter);
(2) When designing the AC 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 AC motors be used in highland areas?
Altitude has an adverse effect on motor temperature rise, motor corona (high voltage motor). The following three aspects should be noted:
(1) The altitude is high, the larger the motor temperature rises, the smaller the output power. But when the temperature rises with altitude, it is enough to compensate for the effect of altitude on temperature rise.
The rated output power of the AC 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 AC motor commutation. Pay attention to the choice of carbon brush materia.