Why do cage type rotor energy-saving motors use this groove shape?

Compared with wound rotor motors, cage rotor motors are more widely used. Cage rotor motors have irreplaceable advantages in both production and maintenance aspects. Its main advantage is the degree of freedom in selecting rotor slots for energy-saving motors.

However, for cage rotor asynchronous motors, the starting problem is relatively serious. If the starting problem is solved, the application level of such energy-saving motors can be further improved. In the original article, we mentioned multiple times that improving the starting performance of asynchronous motors can be solved by adjusting the rotor resistance of the motor. How to adjust the rotor resistance of cage type energy-saving motors is a direct manifestation of the improvement of energy-saving motor technology, that is, by changing the rotor conductor slot, the dynamic variation characteristics of rotor resistance during the start-up and operation processes can be achieved.

The first type of slot is the rotor deep slot. The rotor slot of the energy-saving motor is slender. When the energy-saving motor starts, the rotor current frequency is very high. According to the skin effect, the current density of the guide rod decreases from top to bottom. The current effect at the bottom of the rotor slot is small, which is equivalent to reducing the conductor cross-section, increasing the rotor resistance, and naturally reducing the starting current of the energy-saving motor.

This groove is a representative measure to improve the starting performance of asynchronous motors. After the energy-saving motor is started, the skin effect of the rotor current of the energy-saving motor disappears, the current distribution of the rotor wire rod is basically uniform, and the rotor resistance also returns to DC resistance.

Another type of slot is the double cage rotor slot, which is designed with two layers and uses a thinner gap for conduction between the two layers. Two cages can use different conductor materials. The upper cage is an outer cage made of a conductor material with a higher resistance coefficient, while the lower cage is an inner cage made of a conductor material with a lower resistance coefficient. The idea of improving the starting performance of energy-saving motors is similar to that of improving deep slot rotors, and the effect is better. However, the manufacturing difficulty is greater, and the natural material and manufacturing costs are also high, so there is no need for it.

From the difference between double cage conductors, it can be understood that the upper cage of the rotor is mainly used for starting energy-saving motors, while the lower cage of the rotor of energy-saving motors is mainly used for operation. During the start-up process, utilize the skin effect and the high resistance of the upper cage material to improve the start-up indicators; During the operation of energy-saving motors, the smaller resistance value of the lower cage is in line with the operating performance of the energy-saving motor, and the conductivity of the upper cage will not have a negative impact on the operating performance.