Which parameters are related to the operating characteristics of asynchronous motors?

Asynchronous motor is also called induction motor.

The starting performance and overload capacity of induction motors are related to the impedance of stator and rotor of asynchronous motor.

From the theoretical calculation process, it can be seen that in order to have better torque characteristics.

The stator-rotor reactance is not easy to be too large, and in order to prevent heat generation, the squirrel cage induction motor is required to have a larger starting torque, and the starting resistance during the motor starting process needs to be increased.

These purposeful requirements, it is necessary in the three phase induction motor product design process, as well as the manufacturing process to take some technical means.

Let's first understand what is reactance for induction motors?

Similar to the impedance of resistance to current in a DC circuit, capacitance and inductance also impede current in an AC circuit, and are called reactance.

In AC circuit analysis, reactance is the imaginary part of the complex impedance and is used to represent the impedance of inductance and capacitance to current.

Reactance varies with the frequency of an AC circuit and causes a phase change in the circuit current and voltage.

The stator and rotor reactance in induction motors are determined by most three phase induction motors parameters.

For example, the number of turns, pitch, end length, number of slots, slot shape, iron length of the winding.

Stator-rotor air gap, rotor slot slope, etc. will have different degrees of influence on its reactance.

Induction Motor blocking rotor squeeze effect, magnetic leakage, power supply frequency, the asynchronous motor rotation difference will also affect the reactance value.

Correlation between reactance and asynchronous motor parameters

To facilitate understanding, we use qualitative correlation to communicate with you.

Positive correlation means that the parameter increases or decreases with the reactance value, while negative correlation means that when a parameter increases, the reactance value decreases relatively.

The variables positively correlated with stator reactance include: number of turns of stator winding, winding short pitch ratio, power supply frequency, stator slot size, pole pitch and iron length.

The variables negatively related to the stator reactance value include: number of stator slots, number of slots per pole per phase, air gap, number of pole pairs, and saturation and crowding effects.

Variables positively related to rotor reactance values include: number of stator winding turns, winding short pitch ratio, power supply frequency, pole pitch, iron length, rotor slot size, rotor slope slot degree, and end ring diameter.

The variables negatively related to the rotor reactance value include: number of slots per pole per phase, air gap, number of pole pairs, number of rotor slots, and saturation and crowding effects.

Parameters affecting starting current and resistance

Under the normal working condition of the induction motors, the reactance and resistance of the stator and rotor of the motor are basically a constant value, which can be said to fluctuate very little.

However, in the induction motors starting state, the starting current is very high, the top part of the stator-rotor core is in saturation.

At this time the magnetoresistance increases, the leakage resistance of the winding or the upper part of the guide slot, harmonic leakage resistance, sloping slot leakage resistance are decreasing; when the starting current is high and the slot is narrow, the decrease is more obvious.

Thus, for cage motors, the skin effect is enhanced by the design of the rotor slot, which increases the starting resistance of the polyphase induction motors , reduces the starting current of the induction motor, and improves the starting performance of the single phase induction motor.

Given that the cage rotor is a liquid curing process, it is relatively easy to take some measures on the rotor slot shape, such as using convex slot with abrupt change in slot cross-section, knife-shaped slot, etc. to fully utilize the skin effect, and also using double cage slot or trapezoidal slot with small top and large bottom to effectively improve the starting performance of the three phase induction motor.

We will continue to update more knowledge about electric motors.

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It is important to select a motor that is designed to meet the specific requirements of the application.