Single-phase operations of three-phase generators

The ever-increasing demand for power, and the correspondingly greater complexity of power systems, is leading to more severe problems of system reliability. Modern society is so dependent on the usage of electrical power that even a short interruption of service can cause serious problems. A public utility cannot be expected to provide a perfect power supply, since many of the possible causes of a power disturbance are beyond its control. The windings of small diesel-driven three-phase generator sets are often capable of being connected in either a zig-zag or an Edison-delta arrangement, to provide a single-phase supply for standby or emergency purposes. Although many of these generators are genuinely on standby (i.e. they are brought into operation only as a result of a system failure), many others operate continuously in situations where no mains supply is available. The thesis aims to investigate both the steady-state and the dynamic performance of a three-phase salient-pole generator, when reconnected in either a zig-zag or an Edison-delta configuration, and to provide a performance comparison with the more familiar modes of single-phase operation involving line-to-line and line-to-neutral loading. Symmetrical components are used to investigate the steady-state performance and a phase model is used to determine both the steady state and transient performance. Analytical expressions are obtained for the short-circuit currents for various generator connections by utilizing the modified Clarke transformation. The theoretical results from various models are compared with experimental results on a test machine. Losses, efficiency and voltage waveforms for various generator connections are experimentally obtained for the test machine. Results are discussed and suggestions for future research are included.