Relative Weight of Copper Required in Different Direct current, ordinary two-wire system.. three-wire system, all wires same size 66 1.000 .375 .313 Alternating current, single-phase two-wire, and two-phase four-wire 1.000 Two-phase three-wire, voltage between outer and middle wire same as in single-phase two-wire.. 44 Three-phase three-wire. four-wire. .729 1.457 .750 333 The weight of copper is inversely proportional to the squares of the voltages, other things being equal. The maximum value of an alternating e.m.f. is 1.41 times its effective rating. For derivation of the above figures, see Crocker's Electric Lighting, vol. ii. STANDARD SIZES OF ELECTRICAL MACHINES. (Chiefly Selected from Bulletins of the General Electric Co.) Direct-driven Continuous-current Generators for Lighting and Power. Dimensions in inches: A, height of frame above floor. B, diameter of frame at base. C, width of frame base. Belted Generators. Compound- or Shunt-wound. (a) Full load, 125 volts; no load voltage, 120. (b) Full load, 250 volts; no load voltage, 240. Belted Generators. Slow Speed. Form H (Four Poles). Speeds for 220, 230, and 250 volts are the same as for 110, 115, and 125 volts. * Dimensions in inches: A, length over all in direction of shaft, including pulley; B, width or diameter at feet of frame; C, height above floor; D, diameter of pulley: E, face of pulley. + With rails; includes pulley, but not wood base-frame, Moderate-speed Belted Generators. Form H. Small Belted Dynamos and Motors (4-pole). (Crocker-Wheeler Co.) Bi-polar Dynamos and Motors. (Crocker-Wheeler Co.) Poles. Kw. R.P.M. Poles. Kw. R.P.M. (Poles. Kw. R.P.M. (Poles. Kw. R.P.M. 72 250 24 360 125 107 32 810 94 28 810 12 32 1800 94 12 108 250 28 360 107 40 1800 75 60 CYCLES. From 360 to 810 kw. the machines are wound for 370 volts; from 72 to 810 kw. for 480 volts; from 810 to 6000 kw. for 2300 volts; and from 360 to 6000 kw. for 6600 and 13,200 volts. Poles. Kw. R.P.M. Poles. Kw. R.P.M|Poles. Kw. R.P.M Poles. Kw. R.P.M. 72 276 56 360 2700 100 120 84 2700 86 100 1800 112.5 100 From 2 to 360 kw. the machines are wound for 240 volts; from 72 to 1200 kw. for 480 volts; from 72 to 2700 kw. for 2300 volts; from 540 to 2700 kw. some machines are wound for 6600 volts. The kw. ratings in the above table are based on the load that may be carried without a rise in temperature of any part exceeding 40° C. above the surrounding atmosphere when running continuously with non-inductive full load. An overload of 25%, non-inductive, may be carried for two hours without heating more than 55° C. When full non inductive load is thrown off, with fixed normal excitation, the voltage will rise approximately 8%. When full load with 80% power factor is thrown off, with fixed excitation, the rise will be approximately 22%. A rating one-sixth less is given all machines for a rise of temperature not exceeding 35°C. above surrounding atmosphere. Belt-driven Alternating-current Generators. 60 Cycles. H.P.. Poles Speed Weight Induction Motors. 60 Cycles. 75 100 1 2 3 5 7.5 10 15 20 30 40 50 --1800 200 150 12 12 14 720- 600 600 514 210 300 375 600 700 812 1062 1500 2380 3000 3490 5220 6800 9000 11000 Width, ins.* 19 20 22 24 26 29 34 36 Length, 24 28 28 42 43 48 50 60 57 67 77 42 46 46 57 57 57 59 64 78 78 102 * In direction of shaft, Form K motors. Forms L and M are 4 to 10 ins. wider. |