Electric Motors

Electric Motors

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 edition. Excerpt: ... curve plotted between the listed values of d and Wm as abscissae and ordinates respectively gives the 500-volt load-range curve shown in Fig. 89. The corresponding curves for 300, 400, 600, and 700 volts indicated in the same figure could be obtained in the same manner, though for convenience the authors employed the circle diagrams shown later, on pages 155, 156. It is to be noted that the possible load capacity of this machine is greatest at the highest field excitation considered; but at these heavier loads the armature current is excessive, as shown in Fig. 95. When excited so that its armature produces 500 volts counter e.m.f. the motor has about 80 per cent overload capacity before instability is reached. At greater excitations, for example at 600 volts, the SO /OO /20 WO /60 /SO f7f?g/e bet/ree/? Line i/o/ts and /MotorSM/T FIG. 91.--"CURRENT-PHASE SWING ANGLE" CURVES OF 30-KW. SINGLE-PHASE SYNCHRONOUS MOTOR. crest of the power curve occurs at 140 per cent overload. The important fact follows that with a synchronous motor liable to be subjected to widely variable loads, greater stability is obtained by adjusting its field excitation so that the armature e.m.f. is equal to or somewhat greater than the line voltage. Increase of armature voltage should not, however, be carried very high, since the current for a given load thereby becomes too great, causing excessive heating of the machine. For example, the armature current for 30 kw. at 500 volts is 70 amperes; at 600 volts, 82 amperes; and at 700 volts, 120 amperes. The curves between current and phase angle given in Fig. 91 are derived from the values of d and / in the table just preceding. These show that as the angle between line e.m.f. and motor e.m.f. becomes smaller the...show more

Product details

  • Paperback | 86 pages
  • 189 x 246 x 5mm | 168g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236599381
  • 9781236599384