COMPUTERIZED GENERATOR DIFFERENTIAL PROTECTION

This thesis presents a computerized scheme which detects the presence of phase to ground and phase to phase stator faults on power system generators. The fault/no-fault decisions are based on the amplitude ratio of the "fault" and "average-through" currents from a selected generator phase. Techniques for fast amplitude extraction from sampled inputs are evaluated. The proposed protection scheme is amenable to a time-shared digital computer approach. An analog input data pre-processor, used to reduce the sampling requirements of the digitizer, is described. An input data monitor is included to activate the more sophisticated software only when required. Fast acting software is included to restrict subsequent calculations to the data from the faulted phase. Special attention is directed towards making valid amplitude comparisons during the transient period immediately, following fault incidence. A data logging function, which retains and returns information from any conditions analyzed by the software, is included to permit reconstruction of the pre-fault and post-fault currents. The operation of the hardware and software is also reported. The results of extensive tests, performed on single and three phase versions, were used to evaluate the performance of the scheme. Approximately 800 case studies including internal and external faults using a three phase generator, are presented. This research was financed by a National Research Council bursary and grant No. A7249