Squirrel-cage induction motor

The most popiilar form of motor speed control for adjustable-speed pumping is the voltage-controlled pulse-width-modulated (PWM) frequency synthesizer and AC squirrel-cage induction motor combination. The flexibility of apphcation of the PWM motor drive and its 90 percent- - electric efficiency along with the proven ruggedness of the traditional AC induction motor makes this combination popular. 

Alternating-Current Squirrel-Cage Induction Motors. 29-4... 

Alternating-Current Squirrel-Cage Induction Motors These motors are by far the most common constant-speed drives. They are relatively simple in design and therefore both low in cost and highly reliable. Representative prices are shown in Fig. 29-1 for various speeds and horsepowers. 

FIG. 29-2 Typical speed versus torque curves for various NEMA-design squirrel-cage induction motors. (See Table 29-2 for an explanation of design types.)... 

In the preceding discussion of multispeed ac motors note that only induction motors are considered. These have no discrete physical rotor poles, so that only the stator-pole configuration need be modified to change speed. To operate multispeed, a synchronous motor would require a distinct rotor structure for each speed. Thus multispeed is practical only for squirrel-cage induction motors. 

This is a vital relationship, which reveals that during start-up and until such speed, the reactance of the motor windings / 2> the rotor current will also remain almost the same as the starting current and will fall only at near the rated speed. (Refer to the current curves in Figures 1.5(a) and (b)). The initial inrush current in a squirrel cage induction motor is very high. In a slip-ring motor, however, it can be controlled to a desired level. (Refer to Section 5.2.1.)... 

This polyphase (usually three-phase compared to singlephase) motor is the basic work horse of the process industries for general-purpose applications. Characteristics of polyphase squirrel-cage induction motors are... 

Figure 14-6. Typical squirrel cage induction motor performance curves. (Used by permission Bell, C. J., and Hester L. R. Heating/Piping/Air Conditioning, p. 51, Dec. 1981. Penton Media, Inc. All rights reserved.)...

Polyphase, Squirrel-Cage Induction Motors, General Purpose Ratings, 1105, Allis Chalmers Mfg. Co., Milwaukee, WI, May (1957). 

Squirrel-Cago Induction Motor. A squirrel-cage induction motor is one in which the secondary circuit consists of a squirrel-cage winding suitably disposed in slots in the secondary core. 

Single-Phase Sguirrel-cage Motors. Single-phase squirrel-cage induction motors are classified and defined as follows ... 

Figure 3-10 shows the typical torque-speed performance curves for various designs of polyphase squirrel-cage induction motors [9],... 

The most recent development in the starting of squirrel-cage induction motors is the introduction of the electronic soft-start. This principle has been derived from variable-frequency speed controllers using switched Thyristor or power transistor bridges. The supply sine wave is chopped so that a reduced voltage and frequency is applied to the motor.These are gradually increased so that the motor speed rises in a controlled manner, with the starting current limited to any chosen value. 

Good range. Relatively good low speed efficiency. Automatic speed control easy Low cost. Can use squirrel cage induction motor. Automatic control easy... 

Can use squirrel cage induction motors with minimal derating. Good power factor (with most designs). Speed increase possible... 

Standard 541 Form-Wound Squirrel-Cage Induction Motors—250 Horsepower and Larger... 

Standard for Petroleum and Chemical Industry Severe Duty TEFC Squirrel Cage Induction Motors—Up To and Including 500 HP... 

API 541, Form-wound squirrel-cage induction motors— 250 horsepower and larger. 

IEEE 841, Standard for petroleum and chemical industry— Severe duty totally enclosed fan-cooled (TEFC) squirrel cage induction motors — Up to and including 370 kW (500 hp). )... 

---