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The point on the network where the installation is to be made may often be of importance in obtaining a ruling, so approval in one case may not hold true for the entire network. The starting torque which a motor develops is approximately proportional to the square of the voltage at the motor terminals. Thus, at half voltage, a motor will develop only one-quarter of the torque that it will develop at full voltage, or .50 x .50 = .25. To make starting possible, the voltage at the motor terminals must be high enough to provide the starting torque required at the compressor shaft. On step resistance starters with 75% starting taps, the starting torque is approximately 56% of the rated full voltage starting torque of the motor, assuming that the voltage obtained is actually 75% of nameplate voltage. If subnormal line voltage exists, the starting tap voltage will fall below the 75% and the motor torque will be reduced in proportion to the square of the voltage which is actually obtained. For example, a reduction to 70% line voltage would result in .70 x .70, or only 49% starting torque. Most power companies impose limitations on the current drawn during motor starting periods. While these limitations vary considerably, depending upon the power system capacity, close voltage SECTION 5F.H-1XA PAGE 18 DATE 10-66 Printed control and similar factors, they generally fall into two catagories: 1. The maximum allowable current which may be drawn from the line during the starting period. 2. The maximum increment of current increase during the starting period. 1. Maximum Allowable Current - When the limitation is in terms of paragraph (1) above, and the full voltage locked rotor current of the motor being considered is in excess of this maximum permissible limit, it is necessary to use reduced voltage starting equipment. Under this condition it is essential that the motor start and accelerate under reduced voltage. Otherwise, the full locked rotor current of the motor will be drawn as soon as sufficient voltage is applied. If the motor can be started on the first step and accelerated at the reduced voltage, then full voltage locked rotor current will not be drawn from the line during any part of the starting period. 2. Maximum Increment of Current Increase -When the limitation is in terms of maximum increment of current increase, the starting equipment need only be selected with a sufficient number of steps so that no single step will exceed the allowable current increase. The starting torque developed at the various steps is not of importance, except that the motor selected must have sufficient torque to start the compressor when full voltage is finally applied. The fact that compressor motor may not start at any of the reduced voltage steps is of no consequence during the few seconds required for the starter mechanism to act. Reduced voltage starting equipment is now available in several types, both manual and magnetic. The best known are the Step Resistance, Auto Transformer, Wye-Delta and Increment Starter and Motor Combinations. No attempt will be made here to compare the merits of each type, although the starting equipment to be used for any specific application should be discussed with the power company engineers with a view to obtaining their rulings on all matters pertaining to the electrical aspects of the project. Motors of American manufacture in horsepower ranges used on the 5H compressors have full voltage starting torque amounting to 125% of full load torque on ' 'normal torque1' motors and 200% of full load torque on "hightorque" motors. When motors or other manufacture are to be used, the starting torque characteristics should be obtained. Drive Packages - Table 13 indicates the drive package components for the 5F,H standard belt drive packages. Figure 14 and Tables 14 and 15 indicate the data for the flywheel used in each of these packages. SUPERSEDES SECTION 5F.H-1X PAGES 1-42 in U.S.A. DATE 11-63 Table 13 - Belt Drive Packages (60-Cycle, 1750 Rpm Motors) DRIVE PACKAGE PART NUMBER COMPR SPEED RPM MOTOR HP MOTOR PULLEY FLYWHEEL CENTER-TO-CENTER (in ) NUMBER OF BELTS Bore (in ) Pitch Diameter (in) Pitch Diameter (in-) Part Number 5F20-832 1750 3-5 1-1/8 7 4 7 5 5F20-1053 19.0 2 5F20-466 1750 3-5 1-1/8 7 4 7.5 5F20-1053 19 0 2 5F20-406 1750 7-1/2-10 1-3/8 7.4 7 5 5F20-1053 19.0 2 5F 20-496 1750 7-1/2-10 1-3/8 7.4 7.5 5F20-1053 19.0 2 5F20-842 1450 3-5 1-1/8 6.2 7 5 5F20-1053 19.4 2 5F20-476 1450 3-5 1-1/8 6 2 7.5 5F20-1053 19.4 2 5F20-506 1450 7-1/2 1-3/8 6 2 7 5 5F20-1053 19 4 2 5F20-376 1160 3-5 1-1/8 5.0 7 5 5F20-1053 18 4 2 5F20-486 1160 3-5 1-1/8 5.0 7.5 5F30-1053 18.4 3 5F30-476 1750 7-1/2-10 1-3/8 7 4 7 5 5F30-1053 19 0 3 5F30-496 1750 15 1-5/8 7.4 7 5 5F30-1053 19.0 3 5F30-396 1450 7-1/2-10 1-3/8 6.2 7 5 5F30-1053 19 4 3 5F30-466 1450 7-1/2-10 1-3/8 6 2 7.5 5F30-1053 19.4 3 5F30-486 1160 7-1/2 1-3/8 50 7 5 5F30-1053 18.4 3 5F30-506 1750 10 1-3/8 7 4 7.5 5F30-1...

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