The wound rotor motor has a resistor connected in series to the rotor, so that the motor has a sufficiently large starting torque and a very small starting current (the multiple of the starting current is approximately equal to the multiple of the starting torque), and can also achieve a small-range speed regulation function.
Variable frequency motors can realize soft start and speed regulation functions by changing the frequency. In theory, the speed range from 0 to infinity can be smoothly adjusted, but in fact, low speed is related to the low frequency characteristics of the motor, and high speed is limited by the bearing limit operating speed; The safe operating area is from 0 to the rated speed, which can operate at less than or equal to the rated torque, and from the rated speed to the maximum speed, which can operate at less than or equal to the rated power. Therefore, the variable frequency motor has constant torque from 0 to the rated speed and higher than the rated speed. Constant power speed regulation characteristics.
From the structural analysis of the motor, the cage motor has a relatively simple structure, is less difficult to manufacture, and is extremely strong in terms of mechanical strength. It realizes soft starting and speed regulation functions through a frequency converter, and its maximum speed is much greater than that of the three-phase asynchronous winding rotor. Motor and commutator structure DC motor is a very economical and reliable variable speed drive motor structure.
Theoretically, the wound rotor motor can run at variable frequency, but the wound rotor loses the excellent characteristics of external resistance starting and speed regulation. The soft start performance of the variable frequency method is far inferior to that of the squirrel cage motor (the resistance of the wound rotor is small, and the starting torque is small), and the rotor winds There are hidden dangers of electrical faults such as turn-to-ground and phase-to-phase short circuits and high-speed shedding. The reliability problem is far inferior to that of the solid squirrel cage rotor. Therefore, in addition to doubly-fed speed-regulated asynchronous generators or internally-fed speed-regulated asynchronous motors, the winding Line rotor motors generally do not use variable frequency power supply.
Post time: Dec-05-2024