High Efficiency Induction Motors: With ever-increasing energy cost the life-time operating cost of an induction motor can be traded against a high efficiency and high capital cost induction motors. With rising demand for high efficiency or energy efficient induction motors, designers and manufacturers are stepping up their production of such motors. Some of the important […]

### INDUCTION MACHINE

## Inverted Induction Machine

Inverted Induction Machine: In a wound-rotor induction machine the three-phase supply can be given to the rotor windings through the slip rings and the stator terminals can be shorted (see Fig. 9.68). Such a rotor-fed induction machine is also called an inverted induction machine. The three-phase rotor current will generate a rotating field in the […]

## Induction machine Dynamics

Induction machine Dynamics: Induction machine Dynamics – In general, the mechanical time-constant for any machine is much larger than the electrical time constant. Therefore, the dynamic analysis can be simplified by neglecting the electrical transient without any loss of accuracy of results. The circuit model of Induction machine Dynamics of Fig. 9.8(b) holds for constant […]

## Isolated Induction Generator Working Principle

Isolated Induction Generator Working Principle: An Isolated Induction Generator Working Principle feeding a load is shown in Fig. 9.61. The delta-connected capacitors across the generator terminals provide the magnetizing current necessary to excite the isolated generator. The voltage build-up will be explained later in this section. As the generator is loaded, the operating frequency depends […]

## Induction Generator

Induction Generator: It has been observed from Fig. 9.14 and Example 9.7 that an induction machine is in generating mode for s < 0 (negative slip). An induction generator is asynchronous in nature because of which it is commonly used as windmill generator as a windmill runs at non-fixed speed. These are used in remote […]

## Classes of Squirrel cage motors

Classes of Squirrel cage motors: Classes of Squirrel cage motors – To cater to the different starting and running requirements of a various industrial applications, several standard designs of squirrel-cage motors are available in the market. The torque-speed characteristics of the most common designs are shown in Fig. 9.58. The effective resistance of the rotor […]

## Double Cage Rotor

Double Cage Rotor: Double Cage Rotor – A rotor design, which though more expensive gives still better starting, and running performances than the deep-bar design, is the double-cage rotor. The squirrel-cage winding in this design consists of two layers of bars short-circuited by end rings. The upper bars have a smaller cross-sectional area than the […]

## Deep Bar Rotor

Deep Bar Rotor: Deep Bar Rotor – The chief advantage of the slip-ring induction motor compared to the squirrel-cage one lies in the fact that while its rotor is designed with low resistance to give good running performance (high efficiency, low slip, etc.), excellent starting characteristic (low starting current, high starting torque, etc.) is simply achieved […]

## Speed Control in Induction Machine

Speed Control in Induction Machine: Speed Control in Induction Machine – Stepless control of speed of induction motors cannot be carried out as efficiently and inexpensively as for dc motors. Various methods of controlling the speed of the induction motor can be visualized by consideration of the speed equation It is seen from this equation […]

## Cogging and Crawling

Cogging and Crawling: Cogging and Crawling – A squirrel-cage rotor may exhibit a peculiar behaviour in starting for certain relationships between the number of poles and the stator and rotor slots. With the number of stator slots S1 equal to or an integral multiple of rotor slots S2, the variation of reluctance as a function […]

## Starting Induction Motor

Starting Induction Motor: At the time of Starting Induction Motor slip being unity, the load resistance with reference to the approximate circuit model of Fig. 9.23 ismeaning thereby that short-circuit conditions prevail. Therefore, the motor current at starting can be as large as five to six times the full-load current. In comparison the exciting current […]

## Circuit Model Parameters

Tests to Determine Circuit Model Parameters Circuit Model Parameters – As the Circuit Model Parameters of an induction motor is similar to that of a transformer, the parameters of the model can be obtained by means of nonloading tests as in the case of the transformer—no-load test (corresponding to the OC test on the transformer) and the […]

## Torque Slip Characteristic

Torque Slip Characteristic: The expression for Torque Slip Characteristic (T(s)) is easily obtained by finding the Thevenin equivalent of the circuit to the left of ab in Fig. 9.12. The circuit then reduces to Fig. 9.13 in which it is convenient to take VTH as the reference voltage. Equation (9.22) is the expression for torque […]

## Power Across Air Gap Torque Power Output

Power Across Air Gap Torque Power Output: Power Across Air Gap Torque Power Output – The circuit model of Fig. 9.7(e) is redrawn in Fig. 9.10. The power crossing the terminals ab in this circuit is the electrical power input per phase minus the stator loss (stator copper-loss and iron-loss) and hence is the power […]

## Approximate Circuit Model

Approximate Circuit Model: An Approximate Circuit Model of an induction motor, which results in considerable computational ease in analysis, is obtained by shifting the shunt branch in Fig. 9.8(a) to the input terminals as shown in Fig. 9.9. This step is not so readily justified as in a transformer owing to the relative magnitude of the […]

## Development of Circuit Model

Development of Circuit Model(Equivalent Circuit): Development of Circuit Model – As we shall be mostly dealing with phasor magnitudes the superbar on phasor symbols would only be used for phasor equations.In Sec. 9.3 the behaviour of the induction machine was studied in terms of the basic field phenomenon. The attempt here was purposely focussed on […]

## Principle of Operation of Induction Motor

Principle of Operation of Induction Motor: The Principle of Operation of Induction Motor Figure 9.4 shows the cross-sectional view of an induction motor. The stator is fed from a 3-phase supply of voltage V/phase and frequency f Hz. The rotor is wound* 3-phase for as many poles as the stator and is short-circuited. It is […]