. A text-book of electrical engineering;. bove that the curve is a cosine curve, andis consequently displaced 90° from the sine curve of the current. This willbe made plainer if we determine the magnitude and direction of the self-induction at several critical moments during the period. The current curve is represented by the thick black line in Fig. a = o, sin a = o, but cos a = i. This is the moment when the currentpasses through zero and the of self-induction has its maximum value,as seen from equation (118) on page 245. The current curve is steepest atthis point, w
. A text-book of electrical engineering;. bove that the curve is a cosine curve, andis consequently displaced 90° from the sine curve of the current. This willbe made plainer if we determine the magnitude and direction of the self-induction at several critical moments during the period. The current curve is represented by the thick black line in Fig. a = o, sin a = o, but cos a = i. This is the moment when the currentpasses through zero and the of self-induction has its maximum value,as seen from equation (118) on page 245. The current curve is steepest atthis point, which means that, although there is no current at the moment,yet the rate at which the current, and with it the flux, is changing is then amaximum. That the induced in the coil is negative follows at oncefrom the fact that it opposes the growing current and tends to keep up thed37ing current. When the angle a is equal to 90° we have sin a = i and cos a = 0. Thecurrent is then a maximum and the induced is equal to 0. At the. Fig. 238 moment when the current is a maximum, the current curve in Fig. 238 isparallel to the base, and for an instant both current and flux are is therefore no cutting of lines at this moment, and the dotted curvemust pass through the base line at the point representing a = 90°. By finding the various points on the curve e^ in this manner, the wholecurve can be drawn, with the result that the of self-induction is foundto lag 90° behind the current. This point should be carefully noticed, sinceone might easily come to the conclusion that, as the curve e^ in Fig. 238is further to the right than the curve i, the is therefore ahead of thecurrent. This conclusion is quite wrong, for we see that the curve e^ reachesits maximum value at a time when the curve i has already passed its maxi-mum. Hence the of self-induction lags behind the current by aquarter of a period or by an angle of 90°. This is made clearer
Size: 2073px × 1206px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, bookidcu3192400440, bookyear1920
