Category: THREE-PHASE INDUCTION MOTORS

The ratio of rotor output (i.e., mechanical power developed in rotor neglecting mechanical losses) to the rotor input is called the rotor efficiency. Example 12.14 The power input to a three-phase induction motor is 80kW. The stator losses in total 1.5 kW. Find the total mechanical power developed if the motor is running with a…

We have seen that the electrical power developed in the rotor is converted into mechanical power which is given by the following relation: Mechanical power developed in the rotor  The rotor copper losses  From power flow diagram,   Rotor input = Mechanical power developed + rotor copper losses From eq. (12.3) and (12.4), we get,  ∴ Rotor copper…

Electrical power input is given to the stator. There are stator copper and iron losses and the remaining power, that is, stator output is transferred to the rotor through magnetic flux called rotor input. In the rotor, there are rotor copper losses, and the remaining power is converted into mechanical power called mechanical power developed…

The major losses in an induction motor are as follows:

When load is applied on the induction motor, its speed decreases slightly and slip increases. Therefore, rotor current I2 increases. Simultaneously, to meet with this load, motor draws extra current from the supply mains similar to that of a transformer. In fact, power is transferred through magnetic field or flux. The complete circuit diagram and phasor diagram…

In slip-ring, induction motor rotor circuit can be opened. Under this condition, when stator is connected to three-phase supply, it draws a very small current called no-load current I0. This current has two components, that is,working component Iw and magnetizing component Imag. Working component is in phase with the supply voltage, and it supplies the stator iron losses. Whereas…

Similar to rotor, the stator winding of the motor also has resistance R1. The flux produced by stator winding linking with its own turns only (leakage flux) produces leakage reactance X1. Of the total voltage V applied to the stator, a part of it is consumed by stator resistance (I1Rl) and leakage reactance (I1X1) and the remaining is utilized…

The various parameters and electrical quantities are represented on the circuit diagram, as shown in Figure 12.13. The rotor current is given by the following expression: Fig. 12.13  Rotor circuit The other expression for the rotor current is  (dividing the numerator and denominator by S) This expression gives a convenient form of equivalent circuit as shown in Figure 12.14.…

The rotor circuit diagram of an induction motor is shown in Figure 12.12. Fig. 12.12  Rotor circuit of an induction motor as per its parameters Under running condition Rotor-induced emf = E2 = S × E2s Rotor impedance, Rotor current, Rotor power factor,

The total opposition offered to the flow of rotor current by the rotor circuit is called the rotor impedance. Rotor impedance,  = R2 + jX 2 = R2 + = jSX2s Magnitude of rotor impedance,