RELlABILITY EVALUATION OF POWER SYSTEMS INCLUDING PROTECTION SYSTEM FAILURES

Power transmission systems are becoming increasingly complex as the demand for electric energy increases. The protection system plays an important role in achieving high reliability by recognizing and isolating any abnormal condition in the network within minimum possible time and with a minimum effect on the healthy system. The protection system itself is, however, also a potential source of failure. This thesis describes the different failure modes within the protection system and their effect on load point reliability indices. A number of techniques are available for reliability evaluation of power systems. Protection systems are generally assumed to be perfectly reliable in most of these techniques. Simple equations are developed in this thesis to include protection system failures in transmission system reliability evaluation. These equations can be used in conjunction with the cut set approach to evaluate the outage frequency and duration indices at different points in a transmission system. Terminal related outages resulting in the removal of line and/or generating units can occur in a power system because of faults on the protection system i.e. ground fault on a breaker, a stuck breaker or relay condition, battery failure etc. These failures are normally of short duration but can result in multiple outages of current carrying components. The effect of such outages on the reliability indices of a composite· generation and transmission system can be significant. This thesis describes and illustrates the cause and effect of terminal related outages using the configurations of two practical substations. Models suitable for including their effects in the reliability analysis of a composite generation and transmission system are also described. The results of the composite system are calculated including protection system failures using a 5-bus test system. The resulting indices are then used as starting values in the evaluation of the reliability indices of a hypothetical distribution system supplying a group of individual customer loads