The Diseases Of Electrical Machinery

 uu. uii> 80 THE DISEASES OF kilowatts. Now i horse-power of mechanical power is equal to 746 watts of electrical power. If a dynamo supply 10,000 watts, and in doing that takes 15 horse- power, the efficiency is = 0*91 =91 per cent. If a motor takes 10,000 watts and gives out 12 horse-power on the shaft, its efficiency is 12 x ^4-6 10,000 = o‘89 = 89 per cent If a transformer takes in 20 kilowatts and gives out 19 kilowatts, its efficiency is = o*95 =95 per cent. It is clear that in this process of transformation which takes place in an electric machine, being either from mechanical energy into electrical energy (dynamo), or electrical energy into mechanical energy (motor), or finally, from electrical energy at one volt- age into electrical energy at another voltage (trans- former), losses in energy must occur inside the machine. Otherwise the energy put in and taken out in a given time would be equal; we would have 100 per cent efficiency, and the problem of perpetual motion would be solved. We know the various losses within our electric machines very accurately, and will only mention the loss in the coils of the armature and of the field-magnets ; the losses in the laminated iron cores ; losses through eddy-currents ; friction. in bear- ings, air-friction, brush friction and resistance, etc. etc. In the following method it is unnecessary to separate out all the above losses. We must, however, under-