Document VJM8ne1859VzOdo9BdNkMn11N

642 CHAPTER 45 1959 Guide Table 3 .... Classification of Motors Type Speed Characteristics Fvtt Voltage Sturt*ig Torque Starting HP Kenge Application See Footnote* (o) to (e) Constant Spend Drive* Polyphase a-c Single-phase a-e - Squirrel-cage general Constant purpose Design A Normal 1-2.5 High 6-8 All times' times (a) Fans and (c) centrifugal pumps and centrifugal com pressors Squirrel-cage Design B Constant Normal 1-2.5 Normal 5- Medium times' 6 times Small (a) Fans and centrifugal pumps and centrifu gal compressors Squirrel-cage Design C Constant High 2-2.5 Normal 5- Medium times' 6 times Small (b) Reciprocating pumps (e) and compressors started loaded Squirrel-cage Design F Constant Low 1.25 Low 4 times Medium Large Fans, centrifugal pumps, and compressors Wound rotor Constant or High 1-2.5 Low 1-3 All variable times times (with secondsry control) (o) Hoists (b) reciprocating pumps and compressors (c) and frequent (e) or hard start Synchronous high speed Exactly con- Normal 0.75- Normal 5- Medium stant 1.75 times 7 times Large (a) Fans and centrifugal pumps and centrifu gal compressors Synchronous low speed Exactly con- Low 05-0.4 Low 3-4 Medium stant times times Large (a) Reciprocating compressorsstarting un- . loaded Two value capacitor Constant . High Normal Small (6) Pumps and compres sors Permanent split capaci Constant tor Capacitor start Constant Repulsion Induction Constant Low Moderate High Normal Normal Normal Fractional (o) Fans, Blowers Small Frac tional Medium Small (a) Fans and pumps (a) Fans (b) pumps and compres sors Split phase Constant anc Normal adj ustable Normal Fractional (a) Fans (b) pumps and compres sors (d) fans--direct to values below 50 percent. Fig. 3 illustrates the character istics of wound-rotor motors. Synchronous motors are used for continuous duty applica tions at constant speed where efficiency and power factor are important. Another advantage of these motors is that of lower initial cost in large sizes and for low speeds when com pared with squirrel-cage type motors. The outstanding advantage of the synchronous motor is that its power factor can be changed to compensate for the low power factor of other drives in the same location. lagging power factor is an inherent characteristic of all induction apparatus, such as induction motors and neon signs. Unless synchronous motors or capacitors are installed, the plant power factor may be comparatively low. This does not Motors and Motor Controls 643 Table 3 .... Classrficatkxn of Motors (Continued) Type fufl VoHage Cbarocferistics Starting Torque Starting Current HP Kongo Sou Footnotet (a) to () Adjatobl* Spaed Drive* Squirrel-cage high slip. Variable Transformer adjust ment Normal Normal Medium Small (a) Fans Polyphase a-c Squirrel-cage separate Constant winding or regrouped multi- poles speed Normal or Normal or All high low (o) Fans (b) pumps and (c) compressors Wound rotor Variable High Low All (with secondary control) ' (a) Fans (b) centrifugal pumps and compressors Repulsion Variable High' Normal Low and Fractional (a) Fans, centrifugal pumps (b) compressors Single-phase a-c Capacitor low torque Variable two Low. tapped winding speed Capacitor low torque Variable transformer adjust ment Low Normal Fractional (d) Fans, direct Low Fractional (d) Fans 8plit phase regrouped Constant poles Normal Normal Fractional (d) Fans c. Drives h*vu| amHium or low starting tnqw aad inertia WJ2> mob aa bu and eeatrilugal pomp* or reciprocating pumpa and eomptesaore etarted unloaded, h. Drive* having high starting torques, *ocb as imprecating pumpa and eompnmcn started loaded. e. Simitar to (a) except wtmre frequent or hard starting (large WSt} requires a hifkr starting and accelerating torque. i~ Fans direct connected. . Stoker drives. /. Torque depends on hp rating and speed. See NBMA Standard MGM.10 os Motors aad Generator*. Table 4 .... Locked-rotor Current of Three-phase, 60-cyde Motors at 220 Volts b Ss.'HP Design 8, C, and O Ampere* Deiign f Amperes Design 8, C, HP end D Ampere* 1 or less 1H 2 3 5 24* 35 45 60 90 .30 40 50 60 75 435 580 725 870 1085 270 360 450 540 675 nt 10 15 20 25 120 150 220 290 365 100 1450 125 1815 150 2170 200 2900 900 1125 1350 1800 * The locked-rotor current of three phase, -cycle, constant-speed. Induction tnoton, measured with rated voltage and frequency impressed and with rotor locked, shall not imiul the tabulated values. b Locked-rotor current at other voltages shall be inversely proportional to the voltage. * Far 1 hp or lees the value a given per hp. of Wound-rotor Motors I