The Diseases Of Electrical Machinery

ELECTRICAL MACHINERY. 81 stand how we may classify these different losses in groups. It can be seen that the loss in the armature wihd- ing, in the thick wire winding of compound-wound machines, in the stator winding and rotor winding of induction motors, and finally, in the windings of transformers, can be calculated by measuring the electric resistance in ohms, and by finding out the full load current This loss is then equal to the resistance multiplied by the square of the current, R x C2. It is equaHy clear that the loss in the Held-magnet winding of a shunt machine is known, if one knows correctly the voltage and the current flowing through the windings when the armature is at full load. The loss is equal to the voltage multiplied by the shunt current Although the above losses in the copper conduc- tors can be very simply measured as soon as the resistance is known (as can be at any time found out by sending a sufficiently heavy current through the Circuit, and measuring the current and the volts be- tween the ends of that resistance, the resistance being equal to the volts divided by the amperes), the calcu- lation of the losses in the iron and of the friction losses is very difficult. It becomes, however, easy to get at these losses experimentally by running the machine (whether dynamo or motor) light, as a motor, at full voltage and full speed. When so running, one