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close this bookElectrical Machines - Basic Vocational Knowledge (IBE - Deutschland; 144 pages)
View the documentIntroduction
Open this folder and view contents1. General information about electrical machines
Open this folder and view contents2. Basic principles
Open this folder and view contents3. Execution of rotating electrical machines
Open this folder and view contents4. Synchronous machines
close this folder5. Asynchronous motors
View the document5.1. Constructional assembly
close this folder5.2. Operating principles
View the document5.2.1. Torque generation
View the document5.2.2. Asynchronous principle
View the document5.2.3. Slip
Open this folder and view contents5.3. Operational behaviour
Open this folder and view contents5.4. Circuit engineering
View the document5.5. Application
View the document5.6. Characteristic values of squirrel cage motors
Open this folder and view contents6. Direct current machines
Open this folder and view contents7. Single-phase alternating current motors
Open this folder and view contents8. Transformer
 

5.2.1. Torque generation

The rotating field immediately runs at low inertia when a three-phase alternating voltage in connected to the stator winding. During switching on the stator - because of its inertia mass - is still at a standstill. The magnetic flow change resulting from the rotating field induces the voltage U2 in the rotor. This drives the rotor current I2 in the short circuited rotor circuit.


Figure 52 - Duplicate of a rotor circuit

U voltage, I current, XL reactance, R ohmic resistance, Z impeder resistance

The rotor current I2 is made up of an ohmic share I2W and a reactive share I2b


Figure 53 - Indicator diagram of rotor currents

Ib reactive current, IW eddy current, I2 rotor current

The ohmic share I2W of the rotor current makes up the torque along with the rotating field according to the equation

M = c • Φ1• I2W, and with

I2W = I2• cos φ2

the torque being:

M = C • Φ1• I2• cos φ2

The mode of operation of the asynchronous motor can be illustrated by means of the following operating chain

UI→ I1→ Φ1 rotating field → U2→ I2 (I)2W → M

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