Theory and calculation of alternating current phenomena . /- ^^ \ / ^ ^^ V (iu - lUU99989796 ^ f^.. ^ ^ \ i PO VER FAC TOR —- ?—, .^ ^ 90 __ >(Pp J^PA J ?^ r^ pc/ 30 \ / \ / \ 70 1 / / 1 SO / «( = 2 ?00 V / / e n2180 V y y z =sl + 4J y / 30 P = 2 15 KW.^ X / y 20 ->f j5> y ^ 10 ^ 0 1 w 2t K) Z\ )C 4 ra 4lL0\« K)ATT c 3 )0 71 K) 8 w 901 o Fig. 168. 229. I. Load Curves of Synchronous Motor. Of special interest are the load curves of the synchronousmotor, or curves giving, at constant excitation, e = constant,the current, power-factor, efficiency and apparent efficiency as SYNCHRONOUS MO
Theory and calculation of alternating current phenomena . /- ^^ \ / ^ ^^ V (iu - lUU99989796 ^ f^.. ^ ^ \ i PO VER FAC TOR —- ?—, .^ ^ 90 __ >(Pp J^PA J ?^ r^ pc/ 30 \ / \ / \ 70 1 / / 1 SO / «( = 2 ?00 V / / e n2180 V y y z =sl + 4J y / 30 P = 2 15 KW.^ X / y 20 ->f j5> y ^ 10 ^ 0 1 w 2t K) Z\ )C 4 ra 4lL0\« K)ATT c 3 )0 71 K) 8 w 901 o Fig. 168. 229. I. Load Curves of Synchronous Motor. Of special interest are the load curves of the synchronousmotor, or curves giving, at constant excitation, e = constant,the current, power-factor, efficiency and apparent efficiency as SYNCHRONOUS MOTOR 335 function of the load or output P = Po — (friction + core loss +excitation). Such load curves are represented in Figs. 1G6 to170, for e = 1600, 2000, 2180, 2400, 2800 volts. They canbe derived from Fig. 105 as the intersection of the curves Po =constant with the vertical lines e = constant. Hence, while an induction motor has one load curve only, asynchronous motor has an infinite series of load curves, depend-ing upon the value of 100 i 400 500 COO KILOWATTS Fig. 169. For low values of e (e = IGOO, under excitation, Fig. 166),the load curves are similar to those of an induction current is lagging, the power-fa(;tor rises from a low initialvalue to a maximum, and then falls again. With increasingexcitation (e = 2000, Fig. 167) the power-factor curve rises tovalues beyond those available in induction motors, approachesand ultimately touches unity, and with still higher excitation(e = 2180, Fig. 168) two points of unity power-factor exist, atP = 20 and P = 450 kw. output, which are separated by arange with leading current, while at very low and very high loadthe current is lagging. The first point of unity power-factor 336 ALTERNATING-CURRENT PHENOMENA moves toward P = 0, and then disappears, that is, the currentbecomes leading aheady at no-load, and the second point ofunity power-factor moves with increasing excitation towardhigher loads, from P = 45
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