Document gzZz5OGVXBopRezL7d3q5pDJ

608 CHAPTER 35 1946 Guide d-c Type 1. Shunt 2. Compound . 3. Series Table 1. Classification of Motors Speed Charac teristics Full Voltage Starting Torque Starting Current - ' .. ' Hp Range - Type of Application See Footnotet Constant Speed Drives Constant I Normal , Normal All '(with controller) Variable High Normal (with controller) All Variable High Normal (with co itroller) Small (c) centrifugal pumps and centrifugal compressors (6) (c) (e) Reciprocal ing pumps and frequent or hard . starting (d) Fans direct connected Poly.phase 4. Squirrel-Cage Constant ` Normal General Purpose 0.8t1.5 Class A times High 6-8 times 5. SQuiirel-Cage Class B Constant Normal 0.8-1.5 times Normal 5-6 times 0. Squirrel-Cage Class C 7. Wound Rotor Constant , Constant or Variable High 2-2.6 times Normal 5-6 times High Low 1-2.5 1-3 times times (with secondary control) 8. Synchronous -High Speed Exactly Constant Normal 0.75-1.75 times Normal 5-7 times 9. Synchronous Low Speed Exactly Constant Low 0.3-0.4 times Low 3--4 times All */ Medium Small (c) centrifugal pumps and centrifugal compressors ' fugal pumps and centrifugal com pressors Medium Small (5) Reciprocating ; pumps * (e) and compressors started loaded AU (6) reciprocating pumps and compressors (c) and frequent (e) or hard start Large Medium Large trifugal pumps and centrifugal com pressors compressors starting unloaded 10. Capacitor Constant High Normal 11. Capacitor Fan Constant Normal > Normal Single PHASE a-c 12. Capacitor Start Constant Induction Run 13. Repulsion Induction. Constant High High Normal 14/ Split Phase Constant and Adjustable Normal Normal Small Small V. . (6) Pumps and compressors ' (a) Fans, centrifugal pumps Fractional (b) pumps and . compressors. Medium Small ' (6) pumps and compressors Fractional (a) Fans (b) .pumps and compressors (d) fans--direct tApplications: , . a. Drives having medium or low starting torque and inertia (WR1) such as fans and centrifugal pumps or reciprocating pumps and compressors started unloaded. b. Drives having high starting torques, such as reciprocating pumps and compressors started loaded. c. Similar to (a) except where frequent or hard starting (large WR}) requires a higher starting arid accelerating torque. . 8u d. Fans direct connected. . Stoker'drives. J ' Motors and Motor Controls 609 Power Supply ' Table 1. Classification of Motors--(Concluded) Type Speed Charac teristics Full Voltage Starting Torque Starting Current Hp Range Type of Application, See Footnote* t, Adjustable, Speed Drives 15. Shunt Field Adjustment Constant Normal Normal ' AU (with co itroller) (a) Fans and (e) centrifugal pumps d-c 16. Armature Variable Normal Normal AU . fa) Fans and Resistance (with co itroller) (t) centrifugal pumps Adjustment 17. Variable Voltage Constant' Normal Normal Control (with co itroller) All (d) Fans and centrifugal pumps Poly phase a-c 18. Squirrel-Cage High Slip. Transformer Adjustment Variable 19. Squirrel-Gage Constant Separate Wind Multi- ing or Regrouped Speed Poles 20. Wound Rotor Variable Normal. Normal Normal or High Normal or Low High Low (with se>condary cont rol) 'Medium Small ' All All (a) Fans (a) Fans (6) pumps and (c) compressors () Fans () centrifugal-pumps and compressors 21. Repulsion Variable High Single Phase a-c 22. Capacitor Low Torque Tapped Winding 23. Capacitor Low Torque Trans former Adjust ment Variable Two Speed Low Variable Low 24. Split Phase Constant Normal Regrouped Poles Normal Normal Low Normal Low and () Fans--centrifugal Fractional 'pumps () compressors Fractional (d) Fans, direct Fractional (d) Fans Fractional (d) Fans for starting the motor; (3) overload protection for the motor; (4) pro tection against low voltage; and (5) means for varying the motor speed. Full voltage starting for motors is preferable because of its lower first cost and simplicity of control. Except for d-c machines, most motors are mechanically and electrically designed for full voltage starting. The starting inrush current, however, is limited in many cases by regulations of power companies because of the voltage fluctuations which may be caused by heavy current surges. It is therefore often necessary to reduce the starting current below that obtained by across-the-line starting. The power supplier- should . be consulted to determine' the allowable inrush current for any given location. The choice between full voltage and reduced voltage starting is governed almost entirely by inrush current limitations. The starting torque of all motors varies with the starting current and.it is therefore necessary to insure that the motor is supplied with sufficient current to develop enough torque to accelerate the load. In present practice overload protection of motors is- obtained by use of thermal overload inverse time limit type protection. The usual setting of such protection devices is at 125 per cent overload, the element trip-