Document 3J55NKg04Ovam8b7MqMwMwjND

638 CHAPTER 44 1959 Guide *S. R. Lewis: Testing and rating of air cleaning devices used for general ventilation work (ASIlVE Tbamsactxoxs, Vol. 39, 1933, p. 277). R. 8. Dill: A test method for air filters (ASHVE TeansACnoxs, VoL 44, 1938, p. 379). ** M. B. Jacobs: Analytical Chemistry of Industrial Poisons, Hazards end Solvents (Interscience Publishers Inc, New York, 1941). J. J. Bloomfield and J. M. Dalla Valle: The Determina tion and Control of Industrial Dust (U. S. Public Health Bulle tin No. 217, 1935). "F. A. Patty: Sampling and Analysis of Atmospheric Con taminants (Industrial Hymens and Toxicology, VoL 1, Interscience Publishers Inc, New York, 1948). nE. E. Gross, Jr.: Noise measuring and sound-control (flefngeratmg Engineering, Vol. 66, May 1957, p. 49). "A. P. Peterson and L. L. Beranek: Handbook of Noise Control (General Radio Co, Cambridge, Massachusetts, 1954). n L. L. Beranek: Acoustics (McGraw-Hill Book Co, New York). " H. P. Olson: Elements of Acoustical Engineering (D. Van Nostrand Co, New York). n American Tentative Standards for Sound Level Meters for Measurement of Noise end Other Sounds (American Stand ards Association, Z24.3-1944). CHAPTER 45 MOTORS AND MOTOR CONTROLS Fundamentals of Motor Selection; Alternating-Current Motors, Types and Control Equipment; Motor Rating; Functions of Motor Contra/ Equipment; Glossary of Motor Terms, Enclosures, Speed Classification and Mounting THE electric motor, available in many different types 1. Mechanical Arrangement. Arrangement of the driven suitable for various services, is now the most widely machine usually determines whether a horizontal or vertical used form of motive power. The equipment for starting, conmotor is needed. Horizontal motors are more generally avail trolling, and protecting these motors varies with the type able and less expensive; most grease-lubricated ball-bearing and with the functions it is desired to attain. Motors are motors will operate in either position. Fractional-horsepower divided into two general classifications, alternating-current waste-packed sleeve-bearing motors are satisfactory for short or direct-current, depending on the power source to be used. -periods of vertical operation where no thrust is involved. FUNDAMENTALS OF MOTOR SaECTlON If shaft is tilted for momentary operation, special con struction of bearing housings will be required for oil-ring- The following characteristics of the power supply should Lubricated sleeve-bearing motors, to avoid loss of lubricant. be determined: (1) whether current is alternating or direct, In case of long periods of tilted operation, bearings suitable (2) voltage, (3) alternating-current phase, (4) alternating- for end thrust may be necessary. Ball-bearing motors with current frequency, (5) voltage regulation, (6) continuity of grease lubrication are suitable for tilted operation. power. Most motors are suitable for mounting with base above a 1. A-C vs. D-C Systems. For most applications, a-c supply horizontal shaft or to one ride of the shaft, provided the is satisfactory since suitable performance can.usually be ob end shields are rearranged. If, during operation, the angle of tained with a-c motors and control. Where special charac the motor (with regard to the horizontal 6haft) changes teristics, such as an extra wide speed range and severe ac more than 10 or 12 deg, a ball-bearing motor will usually be celerating or reversing duty are involved, conversion by required. Sleeve-bearing motors are also applicable within means of motor generator sets, by rectifiers, or in special, the angle given if modified oil gages are provided. cases by converters, may be justified. On portable machines, motors of greater compactness and 2. Voltage. Standard conditions of voltage and frequency are the values listed on the n*nr>g plate of the motor. Reason able horsepower design limits are given in Table 1. Power lines are often given voltage ratings known as nominal system voltages which are numerically slightly different from the standardized motor voltages. 3. Phases. Three-phase power supply is most desirable, but only single-phase is offered for-most residential and rural districts. 4- Frequency. Sixty-cycle systems predominate in the United States. In foreign countries, 50-cycle systems are com mon and nominal system voltages are frequently different. 5. Voltage Regulation. The voltage regulation of the power supply should be known in order to select motors which will deliver sufficient torque even with the probable drop in voltage, to start and carry the load. All induction motor less weight than standard may be required, and special bear ing construction may be needed, except for ball-bearing mo tors. Direct connection should always be considered where machine speed coincides with available motor speed. Maintenance, efficiency, power factor, space, and initial cost, will determine the choice between direct connection and other methods, such as belt, chain, or gear drive. When direct connection is possible (where parts of the driven ma chine, such as shaft or bearings, are common with the motor structure) a built-in construction may be advantageous. Belt Drive. Diameters and widths of pulleys or sheaves and center distances are factors in determining motor-bearing pressures and shaft deflection. Flat belts should not run at greater speeds than about 5000 fpm. Application of flat belting to vertical-shaft motors is difficult. Chain Drive. The chain manufacturer should be consulted so that the best drive on a basis of quietness and economy of torques and synchronous-motor starting and pull-in torques operation may be selected. vary as the square of the voltage. Gear Drive. Compactness and arrangement of drive often 6. Continuity of Power. Dips in voltage from switching or indicate gear motors, which are obtainable in a variety of other line disturbances may necessitate time-delay under mechanical constructions with speed ratios of 3 to 1 upwards, voltage protection, and, in case of synchronous-motors, high and are generally limited to about 75 hp nnnimnm. Where torque designs and resynchronizing control. Sustained low the pinion of ordinary spur gearing is mounted on the motor voltage may necessitate higher torque motors. shaft, two-bearing motors are limited in. horsepower ratings. The following characteristics of the driven machine should Maximum pitch-line speed with steel pinions is about 1400 be determined: (1) mechanical arrangement including po fpm. sition of motor and shaft, portability desired, drive connec The selection of the motor part of a gear motor is the tion, and space limitations; (2) speed range desired; (3) as for a conventional motor. horsepower requirement; (4) torque; (5) inertia; and (6) frequency of starting. Space limitations may affect the choice of motor and re quire (a) built-in construction; (6) a gear motor; (e) forced' 639