Electrical Machines - Basic Vocational Knowledge (IBE - Deutschland; 144 pages) Introduction 1. General information about electrical machines 2. Basic principles 3. Execution of rotating electrical machines 4. Synchronous machines 5. Asynchronous motors 5.1. Constructional assembly 5.2. Operating principles 5.2.1. Torque generation 5.2.2. Asynchronous principle 5.2.3. Slip 5.3. Operational behaviour 5.4. Circuit engineering 5.5. Application 5.6. Characteristic values of squirrel cage motors 6. Direct current machines 7. Single-phase alternating current motors 8. 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