1. Why can't general motors be used in high-altitude areas?
The altitude has adverse effects on motor temperature rise, motor corona (for high-voltage motors), and DC motor commutation. The following three aspects should be noted:
(1) The higher the altitude, the greater the temperature rise of the motor, and the smaller the output power. But when the temperature decreases with the increase of altitude enough to compensate for the impact of altitude on temperature rise, the rated output power of the motor can remain unchanged;
(2) High voltage motors should take anti corona measures when used in high-altitude areas;
(3) The altitude is unfavorable for the commutation of DC motors, and attention should be paid to the selection of carbon brush materials.
2. Why does the motor generate shaft current?
The current in the shaft bearing seat base circuit of the motor is called shaft current.
Reason:
(1) Magnetic field asymmetry;
(2) There are harmonics in the power supply current;
(3) Poor manufacturing and installation, resulting in uneven air gap due to rotor eccentricity;
(4) There is a gap between the two semicircles of the detachable stator core;
(5) The selection of the number of assembled stator cores with fan-shaped stacking is not appropriate.
Hazard:
Causing erosion on the surface of motor bearings or rolling balls, forming point like micropores, deteriorating bearing performance, increasing friction loss and heat generation, ultimately leading to bearing burnout.
Prevention:
(1) Eliminate pulsating magnetic flux and power harmonics (such as installing AC reactors on the output side of the frequency converter);
(2) When designing the motor, the bearing seat and base of the sliding bearing are insulated, and the outer ring and end cover of the rolling bearing are insulated.
3. Why is the motor not suitable for light load operation?
When the motor operates under light load, it can cause:
(1) Low motor power factor;
(2) Low motor efficiency;
(3) It will cause equipment waste and uneconomical operation.
4. Why motors that cannot be started in cold environments?
If the motor is exposed to low temperatures for too long, it may:
(1) Motor insulation cracking;
(2) Freezing of bearing grease;
(3) Solder powdering of wire joints.
Therefore, the motor should be heated and stored in a cold environment, and the winding and bearings should be inspected before operation.
5. Why can't a 60Hz motor use a 50Hz power supply?
When designing motors, silicon steel sheets are generally operated in the saturation zone of the magnetization curve. When the power supply voltage is constant, reducing the frequency will increase the magnetic flux and excitation current, leading to an increase in motor current and copper loss, ultimately resulting in an increase in motor temperature rise. In severe cases, the motor may also be burned out due to overheating of the coil.
6. Can clicking on soft start save energy?
The energy-saving effect of soft start is limited, but it can reduce the impact of start on the power grid and achieve smooth start to protect the motor unit. According to the theory of energy conservation, due to the addition of relatively complex control circuits, soft start not only does not save energy, but also increases energy consumption. However, it can reduce the starting current of the circuit and play a protective role.
7. Why is a leakage circuit breaker prone to tripping when using a frequency converter?
This is because the output waveform of the frequency converter contains high-order harmonics, and the motor and the cables between the frequency converter and the motor will generate leakage current, which is much larger than when driving the motor at power frequency, resulting in this phenomenon.
