Differentially Connected Motor Performance (Electric Motors)

4.7.3
The procedure for calculating the performance of differentially connected motors is the same as for cumulative motors except for the full load air gap flux ^gfl. In this case, the magnetic circuit is solved by subtracting flux due to the ampere-turns of the series winding from the shunt field flux. From the preceding formulas, one can see that a smaller full load air gap flux ^gfl will cause the full-load speed to increase over the no-load speed.
One can see that if the efficiency is estimated incorrectly, the calculated performance results will be incorrect. This is, in effect, an iterative process which can be done rapidly and accurately with the aid of modern computers.