The testing of continuous current machines in laboratories and test-rooms Volume 1 ; a practical work for students and engineers - Softcover
Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 Excerpt: ...plotting the sum of the voltages between the consecutive bars against the position of the bar, since, with the windings mentioned above, the potential curve is equal to the sum of the field curves. EFFICIENCY Introduction As in the case of other transformations of energy, in the conversion of electrical into mechanical, or vice versa, losses arise which, with dynamos and motors, are of an electrical (magnetic) and mechanical nature. The value of these losses (i.e. the determination of efficiency) is, from the reasons given in Chapter III., of great importance. Though from a commercial point of view the knowledge of the total efficiency is quite sufficient, it is very important for the designer of au electric machine to know how the total losses arising in a machine are comprised. We shall therefore not only deal with the various uiethods for the determination of efficiency of dynamos and motors, but also the methods of finding and separating the individual losses. The efficiency (j) of a machine is equal to the ratio of the power delivered (Pa) and the power consumed (Pc); thus: Consider the transformation of energy in the case of a generator. A part of the mechanical energy supplied to the generator is lost or rather transformed into heat by the mechanical and magnetic frictions. The remainder of this energy is transformed into electrical energy. But not all of the latter can be employed usefully; part of it is required to excite the machine, and another part is lost in the armature winding (ohmic loss). With a motor, of the electrical energy supplied a part is lost in exciting the machine and overcoming the ohmic resistance of its armature. The remainder is transformed into mechanical energy, from which, however, a part is lost in overcoming the mechanica...
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