Squirrel cage motors

Four-Speed, Two-Winding Squirrel-Cage Motors. 29-7... 

The typic medium-sized squirrel-cage motor is designed to operate at 2 to 3 percent shp (97 to 98 percent of synchronous speed). The synchronous speed is determined by the power-system frequency and the stator-winding configuration. If the stator is wound to produce one north and one south magnetic pole, it is a two-pole motor there is always an even number of poles (2, 4, 6, 8, etc.). The synchronous speed is... 

The higher the full load slip, the higher will be the rotor losses and rotor heat. This is clear from the circle diagram and also from equation (1.9). An attempt to limit the start-up current by increasing the slip and the rotor resistance in a squirrel cage motor may thus jeopardize the motor s performance. The selection of starling current and rotor resistance is thus a compromise to achieve optimum performance. 

Figure 1.18(a) Screen protected drip proof (SPDP) squirrel cage motor (Cooling system ICOA1)... 

Figure 1.21 Closed air circuit, air cooled (CACA) squirrel cage motors (likely cooling systems IC6A1A1 or IC6A1A6) (Courtesy BHEL)...

Figure 2.4(a) Equivalent circuit diagram of a single squirrel cage motor... 

A squirrel cage motor is started through an auto-transformer starter with a tapping of 40%. Compare the starting heat with a DDL starting when the motor shaft is free. 

A centrifugal compressor driven through V-belts at a speed of 4500 r.p.m. having the torque curve as shown in Figure 2.18 and a moment of inertia /WK of 2.50 kgm employs a squirrel cage motor with the following parameters ... 

The following are common methods to start a squirrel cage motor, depending upon the limitation, if any, on the magnitude of switching current, / . 

A squirrel cage motor has its 4, on DOL as six times its rated current. Find the required tapping on an autotransformer to limit the starting current to 1.5 times. 

Restriction in starting current and a requirement for high starting torque to accelerate heavy rotating masses sometimes limit the use of a squirrel cage motor. For such applications a slip-ring motor provides a better alternative. 

Speed control in slip-ring motors has been discussed in the previous chapter. Squirrel cage motors have limitations ill their speed control in view of their fixed rotor parameters. Speed variation, in fixed steps, however, is possible in such motors if the stator is wound for multipolcs and such motors arc known as pole changing motors. Up to four different speeds can be achieved in such motors economically, in combinations of 2/4, 4/6. 4/8, 6/8, 6/12, 2/4/6. 4/6/8. 2/4/6/12 and 4/6/8/12 poles etc, or any other similar combination. For limitation in the motor size and tlux distribution, winding sets of more than two are not recommended. I he two windings can be arranged for two. three oi (maximum) four different speeds. 

The above methods provide speed variation in steps, as in squirrel cage motors or in two machines or more, as in frequency converters, and cannot be u.sed for a process line, which requires frequent precise speed controls. Until a few years ago there was no other option with all such applications and they had to be fitted with d.c. motors only. D.C. motors possess the remarkable ability of precise speed control through their separate armature and field controls. In d.c. motors the speed... 

Induction generator This is a standard squirrel cage motor with additional treatment to weather the site conditions. The normal specifications are generally the same as for a standard motor. The permissible voltage and frequency variations are, however, wider as noted below ... 

With the availability of V/f drives and other advanced technologies through static controls, as discussed in Sections 6.2 to 6.4, the use of standard squirrel cage motors for such applications is a preferred choice. 

The normal characteristics of these motors are generally the same as those of a standard squirrel cage motor. 

Vertical hollow shaft squirrel cage motor... 

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