Effect of winding asymmetries and winding connection on small synchronous machines

This paper reports on the study of winding asymmetries in small synchronous generators. These types of generator are commonly used in diesel generator or back-up systems and are usually no more than a few or few tens of kilowatts with two, four or six salient poles. The 3-phase winding is 120 deg pitched but often lap windings are not used, rather a hybrid of concentric winding and double layering is utilized. There are sound manufacturing reasons for this and these are explained. This leads to small asymmetries in the phase-belt inductances and field-induced voltages. This is examined and validated experimentally. The paper discusses the techniques that are used to analyze the machine. These are analytical methods although a discussion about finite element analysis is put forward. The methods address the correct positional coil groupings in the slots to obtain back-EMFs, mutual and self-inductances and line currents. These are obtained over a varying load range.