Document Vj9x1117QLGnxBmov1nKJ16NK

, 646 Chapter 35 1945 Guide manual or magnetic. .In some cases it is desirable also to provide a - disconnect-switch. Fig. 13 illustrates the recommended controls. Typical specifications for single phase motor control are shown on page 645. V.--. GEAR MOTORS A gear motor is a self-contained combination of any type of a-c or d-c niotor and an enclosed speed-reducing gear; providing a more compact and readily adaptable unit than is obtained by using a motor coupled to a gear reducer. Gear motors are available in sizes up to 75 hp with output LINE ACROSS THE LINE STARTING LINE LINE LINESTARTER MOTOR REDUCED VOLTAGE STARTING LINE Arrangements 2, 3,4 and 5 provide automatic push-button starting. Fig. 11. Recommended Controls for Squirrel-Cage Motors shaft speeds from about 4 to 1430 rpm, making it possible to couple dr to connect by gear or chain to nearly any machine. High speed motors are used, generally 1800 rpm on 60 cycles, thus obtaining the advantages of high motor power factor and efficiency. The gearing efficiency is also high, usually about 98 per cent for a single reduction of the helical or spur type, that is, a 2 per cent loss for one reduction or 4 per cent loss . for a double reduction, Consequently, the.over-all performance of the gear motors is much higher than a combination of open gearing, belting, countershaft, or other arrangement, which would otherwise be required. Gear motors are used extensively to drive numerous types of slow speed drives. Besides being more effective than other combination drives in saving space, they are important in reducing maintenance and oper ating hazards. . General Definitions GLOSSARY NEMA is the abbreviation for the National Electrical Manufacturers Association. Speed Regulation (d-c.motors) is the change in speed between no-load and full-load, Motoriand Motor Controls LINE I SAFETY SWITCH | LINESTARTER RHEOSTAT MOTOR LINE LINE 647' SPEED REGULATING CONTROLLER MOTOR Fig. 12. Recommended Controls for Wound Rotor Motors expressed in per cent of full-load speed; for example, a motor having a no-load speed of 1200. rpm and a full load speed of 1140 rpm would nave a speed regulation of 5.6 per cent. Slip (a-c induction motors) is the difference between the motor speed and synchronous speed expressed in per cent of synchronous-speed, e.g.t a 1200 rpm motor operating at 1140 rpm would have a slip of 5 per cent. Torque is an expression of the turning effort developed by the motor at the shaft and is usually expressed in ounce-feet for fractional horsepower motors and in pound-feet for motors of larger ratings. Primary is the term usually applied to the high voltage or line side of a transformer or moor. In the case of the wound rotor motor the primary is the stator winding. .Secondary is the term usually applied to the low voltage or load side of a transformer or motor. In the case of the wound rotor motor the secondary is the rotor winding. SMALL BREAKER LINE I 2 MANUAL STARTER !MOTOR LINE MOTOR LINE NUAL STARTER REDUCED VOLTAGE) MOTOR Arrangements 2,3 and 4 are optional for motors up to 7>4 hp, 220 volts. Fig. 13. Recommended Controls for Single Phase Motors