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.618 CHAPTER 35 1946- Guide Motors arid Motor'Controls , 619 winding motor and :because of the factor of safety provided by two inde pendent windings, the increased cost is frequently worth the difference. Single Phase Motors Single phase induction motors inherently develop no starting torque and are provided with auxiliary windings and devices for starting pur- injeach winding; Motors can be provided in constant torque,' varying torque or constant horsepower ratings. The constant horsepower type of motor is considerably larger them the constant torque motor due to the fact that the same horsepower must be developed-at either reduced speed or high speed. In selecting two-speed motors for fan, pump, blower, or compressor applications, it is usually found that two winding motors are more expensive than the single winding type. The control cost for two-speed, two winding motors, however, is more economical, and therefore the combined price of both motor and control for the two winding motor is only slightly higher. Because of the improved performance of the two TYPE o r SQUIRREL CAGE MOTOR u 3 t2- U So So n 2a 9 33 0 IZ)JD it i* oo- oot4 oon CLASS A g I CLASS e HCLASS C 1 i CLASS 0 g oO Oo oO oO (III '[ T T 1 1' fill ttsfiral! 1 | rM nXn TT1 1 100 3 0Z0Z X * OF FULL MAXIMUM TORQUE" LOAD TORQUE S.v 1 59 3 "h. jJ 3 SSS 111 R&9&I 1 T1 pdettj 11 met 1 11 bli ri ,v ,-st* S3 U -1 s j*Oh a. < e ns o , ,v a < S3 id 33 ot <> ` ft-SAME AS STARTING Fig. 7. Comparative Performance of Squirrel-Cage Motors of-' 30 Hp and Smaller Sizes Fig. 8. Efficiencies and Power Factors for Squirrel-Cage -Induction Motors poses. The motors are classified as to the type. of auxiliary winding provided. Capacitor Start-Induction Run motors develop high starting torque with low starting current and are used for all types of constant speed heavy duty drives such as compressors, pumps, and stokers. During the starting period, a winding with a capacitor in series is connected in the motor armature circuit and when the motor comes up to speed a centrifugal switch cuts the capacitor and second winding out of the circuit. - Capacitor motors, which are ideally suited for small fan drives, are similar to the capacitor start-induction run type except that the capacitor is riot cut out when running.- , Repulsion Start-Induction Run motors develop extremely high starting' torque. They are supplied with a short-circuiting switch which cuts out