. A text-book of electrical engineering;. e of E and V. The total powerPj supplied to the motor in Fig. 355 is <f), while the total powerPi generated electrically by the alternator in Fig. 356 is i. 352 Electrical Engineering • These are evidently equal. Now, on page 325 we established the equation(159) for the value of P^ for a generator, and it is evident that it can bemade applicable to a motor by putting E for V and V for E, giving us Pi = {y — a) + ^.sma (163), where P^ is the power given to the motor, and the short-circuit current /^is given by the equati
. A text-book of electrical engineering;. e of E and V. The total powerPj supplied to the motor in Fig. 355 is <f), while the total powerPi generated electrically by the alternator in Fig. 356 is i. 352 Electrical Engineering • These are evidently equal. Now, on page 325 we established the equation(159) for the value of P^ for a generator, and it is evident that it can bemade applicable to a motor by putting E for V and V for E, giving us Pi = {y — a) + ^.sma (163), where P^ is the power given to the motor, and the short-circuit current /^is given by the equation „ In a similar manner we see that the output P of the motor in Fig. 355is equal to OB. I. cos ^j, which is exactly equal to the output P of the genera-tor, after deducting the I^.Ra loss in the armature, viz. (f) inFig. 356. Thus, the equation (160) found on page 327 for the generator willbe true for a motor if E and V be interchanged. We have therefore £2 P = £■. Jq . sin (y + a) — p^. /o . sin a .(164).. Fig- 357 y is here the angle by which the lags behind the backward pro-jection of the terminal pressure vector. We must now draw curves to show graphically how the power varieswith the angle y. As in Figs. 340 and 341, so here in Figs. 357 and 358,circles are drawn passing through 0 and having their diameters rnchnedto the horizontal by the angle a. In Fig. 357 the diameter is set out belowthe horizontal, and in Fig. 358 above it. Its length in each case is „.Every chord drawn from the point 0 to any other point on the circle, isproduced beyond the circle by an amount a. The heavy curve Pj,obtained in this way, is the locus of the extremities of lines drawn from 0to represent the total power supplied to the motor for the correspondingvalue of y. The vector of the terminal pressure V wUl be vertically down-wards from 0, and y is the angle between E and — V, as shown in the figure. Just as Fig. 357 represents equation (163) so Fig.
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