Document M4nxab8o8V7kVXQwoGdrQnnrM

American Society of Heating and Ventilating Engineers Guide, 1936 Current Type Table 1. Classification of Motors Speed Charac teristics Starting Torque' Starting Current Hp Range Constant Speed Drives Type op Application See Footnotes 1. Shunt Direct 2. Compound 3. Series Constant Medium Medium Constant High Medium or Variable Variable High Medium All All Small (a) Fans and (c) Centrifugal Pumps (6) (c) (e) Reciprocating Pumps and frequent or hand starting (d) Fans direct connected Poly phase 4. Squirrel Cage Constant Medium High All (a) Fans and General Purpose 6-8 Times (c) Centrifugal Pumps 5. Squirrel Cage Constant Medium Medium Medium (a) Fans and Medium Torque 5-6 Times Small Centrifugal Pumps 6. Squirrel Cage High Torque Constant High Medium Medium 5-6 Times Small (b) Reciprocating Pumps (e) and Compressors started loaded 7. Slip Ring Constant High Low All (a) and Hoists Wound Rotor 1-3 Times (b) Reciprocating Pumps ' (c) and Frequent (e) or Hand Starting 8. Synchronous High Speed Constant Medium Medium Medium (a) Fans and 5-7 Times / Large Centrifugal Pumps 9. Synchronous Low Speed Constant Low Low Medium (o) Reciprocating 3-4 Times Large Compressors \ Starting Unloaded 10. Repulsion Induction Single Phase 11. Capacitor 12. Capacitor 13. Capacitor Constant High Medium Medium (a) Fans Small (b) Pumps and Compressors . Constant Low Medium Small (d) Fans--direct All and Constant Medium 6-8 Times Fractional (a) Fans--belt Constant High (b) Compressors and Pumps 752 Chapter 42--Motors and Their Control Current Table 1. Classification of Motors--(Continued) Type Speed Charac teristics Starting Torque Starting Current Hp Ranqe Type op Application See Footnote Adjustable Speed Drives Direct 14. Shunt Field Adjustment 15. Shunt Armature Resistor Constant Medium Medium Variable Medium Medium All . All (c) Fans and (e) Centrifugal Pumps (a) Fans and (e) Centrifugal Pumps PolyPHASE 16. Squirrel Cage Regrouped Poles 17. Slip Ring Secondary Resistance Constant Medium Multi- or High speed Variable High High Low All (a) Fans and (6) Pumps All (a) Fans and (b) Centrifugal Pumps Single Phase 18. Capacitor Variable Transformer Adjustment . _ Low Low Fractional (id) Fans aApplications: a. Drives having medium or low starting torque and inertia (WR*) 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 hand starting (large WR*) requires a higher starting and accelerating torque. d. Fans direct connected. e. Stoker drives. SPECIAL APPLICATIONS A few applications of motors may require special constructions such as splash proof, explosion proof, fully enclosed, and self-ventilated to meet hazardous or special duty conditions. These requirements are frequently encountered in certain industrial applications, in which cases it is neces sary to select the motors from the viewpoint of service conditions, as well as the required operating characteristics to meet the demands of the machines being driven. The general classification of motors used for heating, ventilation and air conditioning is shown in Table 1. CONTROL EQUIPMENT FOR MOTORS In selecting control for alternating and direct current motors it is necessary to determine whether the installation is to be operated by manual or automatic control. The available controls and the function of each group of apparatus may be outlined as follows: 1. Manual Control: a. To establish current. (1) Snap switch. (2) Knife switch. (3) Manually operated contactor. (4) Drum switch. 753