The Diseases Of Electrical Machinery

... J H.ll ... Hil. . llllllllll IUIIIH ............................................MIN...................................IIUUKM ELECTRICAL MACHINERY. 79 ■; ■ CHAPTER V. EFFICIENCY. Many purchasers of dynamos, motors or trans- formers, stipulate for a certain efficiency of the machine, and sometimes demand a test to show that the stipu- lated value has not been exceeded. Here is perhaps, therefore, a suitable place to describe the simplest and most easily comprehended method of measuring the efficiency. By this term we understand the ratio of the energy given out to the energy put in to the machine. In the case of a dynamo, it is the ratio of the electrical energy given out to the mechanical energy supplied to the shaft. For an electric motor, it is the ratio of the mechanical energy given out to the electrical energy put in. And in the case of a transformer, the ratio of the electrical energy given out to that supplied. Both valnes which form the numerator and denominator of a fraction must be expressed in terms of the same kind, and for this purpose it is preferable to express power, whether electrical or mechanical, either in watts or else in -