. A text-book of electrical engineering;. rength. The average over the arc 2y is found as follows: „ I /(»i+v) „ . , „ sinyTT . B = — / B . sm avr . aa = B . ——. sm a,7r. 25—2 388 Electrical Engineering To calculate the torque we shall require the product of the mean fieldstrength and the momentary value of the current. We have . „ _, A sinyTT . 2yn In this equation jg is the momentary value of the current, and B themean value of the field strength over the coil-side at that moment. NoW) the coil-side moves steadily through the field, the angle a^TTvaries from o° to 360°, and, since the v
. A text-book of electrical engineering;. rength. The average over the arc 2y is found as follows: „ I /(»i+v) „ . , „ sinyTT . B = — / B . sm avr . aa = B . ——. sm a,7r. 25—2 388 Electrical Engineering To calculate the torque we shall require the product of the mean fieldstrength and the momentary value of the current. We have . „ _, A sinyTT . 2yn In this equation jg is the momentary value of the current, and B themean value of the field strength over the coil-side at that moment. NoW) the coil-side moves steadily through the field, the angle a^TTvaries from o° to 360°, and, since the value of the product ja. B is proportionalto the square of the angle a^Tr, its mean value can be found in exactly thesame way as the mean power was determined in Section 73. Analogous toequation (115) on page 237, we have A ,p ., _ B .^2 smyTT(^ -hJmeiin - —^ ■ -:^ ■ The force on the coil-side in dynes is found by multiplying togetherthe strength of the field, the absolute current in the wire, and the total length. Fig. 398 of effective wire in the coil-side. Since, however, the same mean force isgiven by every coil-side during a period, the total tangential force on therotor is equal to /, where A J. B. «2 sin vTT „ , , , , /= -. —^—.Z,./: dynes (173). This force acts at an arm equal to the rotor radius r. Since the cylindricalsurface of the rotor is equal to the product of the polar surface Ag and thenumber of poles 2p, we have 2! = ,or r = i-—5^ . TT .L To convert the torque or turning moment from dyne-cm into kg-metres,we must divide by 981, Thus we get ^ _ ^.i^ sinyTT 77 . 40 .9-81. 10 ■ yn •(174)- 120. The Torque of an Induction Motor 389 Since = 5mean, IT Substituting, further, the effective current I^ for Jj/Vz, we get M, = 3-6.:^.,./,. (175). The breadth y becomes o for a squirrel cage, is equal to \ for a coil-winding, and I for a winding like that on the left of Fig. 366. The rati
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