Why Are The Variable Frequency Motors All Cage Rotor Structure

The winding rotor motor makes the motor have a large enough starting torque through the way of rotor series resistance, and the starting current is very small (the starting current multiple is about equal to the starting torque multiple), and the function of small range speed regulation can also be realized.

Frequency conversion motor can be changed by changing the frequency method to achieve soft start and speed regulation function, in theory: 0 to infinity speed range can be smooth speed regulation, but in fact, low speed is related to the low frequency characteristics of the motor, high speed is limited by the bearing limit running speed: the safe operation area is 0 to rated speed range can be less than or equal to rated torque operation, rated speed to the highest speed range can be less than or equal to rated power operation, therefore, frequency conversion motor has 0 to rated speed constant torque, higher than rated speed constant power speed regulation characteristics.

From the structural analysis of the motor, the structure of the cage motor is relatively simple, the difficulty of manufacturing is small, the mechanical strength is extremely strong, through the frequency converter to achieve soft start and speed regulation function, the highest speed is much greater than the winding rotor three-phase asynchronous motor and commutator structure DC motor, is a very economical and reliable variable speed drive motor structure type.

Theoretically, the wound rotor motor can be operated by frequency conversion, but the winding rotor loses the excellent characteristics of external resistance starting and speed regulation, and the performance of the frequency conversion mode when soft start is far less than that of the squirrel cage motor (the winding rotor is small in electric yin, and the starting torque is small), and the rotor winding has electrical faults such as inter-turn to ground, short circuit between phases and hidden dangers of high-speed rejection, and the reliability problem is far less than that of the squirrel cage rotor, so in addition to the doubly-fed speed regulation asynchronous generator or the internal feed speed regulation asynchronous motor, the wound rotor motor generally does not convert the frequency power supply.

So, can the frequency conversion motor completely replace the wound rotor motor? The answer, of course, is no, and we will open a separate section to communicate with you about this.