Output coefficient of synchronous machines. A new concept

In the design of synchronous salient-pole generators and motors, current formulas for the output coefficient express this constant in terms either of the apparent power, speed, length of stator core and gap diameter or of the magnetic and electric loading. The paper develops an analysis in which the output coefficient is expressed as a function of the dimensions of the stator core, the magnetic loading and the electric loading related to the temperature rise of the stator winding, in terms of the thickness of insulation and slot dimensions. The output of the rotor is derived as a function of the pole pitch and height of pole. It is shown that there are two optimum values of the mean flux density in the air gap, and that there is also an optimum value of the electric loading, defined as a function of the width of slot. It is also shown that, for a stator designed in accordance with this analysis, there is one value of the height of rotor pole required to accommodate a field coil to establish the m.m.f. required to balance the armature reaction. The theory is illustrated by a series of curves calculated from the parameters of an existing large hydroelectric generator. It is further shown that the overall dimensions and cost could possibly have been reduced by the application of the principles established in this paper.