The Diseases Of Electrical Machinery

84 DISE A SES OF ELECTRICAL MACHINERY. 1. No-load (mechanical and magnetic losses, losses in the stator winding due to the no-load current) = 177 watts, as per test. 2. Additional copper loss at full load (in the stator) = (5’5 X 5’5 - 2-22 x 2-22) x 0*73 x 3 = 55 watts. 3. Copper losses in the rotor. These are propor- tional to the slip. The motor made 1500 revolutions per minute at no-load, and 1420 revolutions per minute at full-load. The rotor losses are therefore— 1800 fi — ——= 99 watts. X 1500/ y The efficiency is therefore— 1800 , „ 70T2 1 1 hh .---= about 0’845, i.e. 841 %. 1000 + 177 + 55+99 We may also deduce from the above experiment the value of the power-factor— cos </> = ______1800______ 220 x 5-5 x V3 = o-86. An example about the efficiency of transformers we consider superfluous, since now the value of the efficiency should be clear after considering the above, namely, equal to the ratio of the watts given out by the secondary to the watts put in to the primary. LONDON : PRINTED BY WILLIAM CLOWKS AND SONS, LIMITED GRF.AT WINDMILL STBEET, W., AND DUKE STBEET, STAMFOKD STBEET, S.E.