The failure rates of overhead distribution system components

A study of 85 rural and 95 urban overhead distribution feeders from the Pacific Gas and Electric system was made to develop generic service time failure rates for seven overhead (OH) component types-transformers, switches, fuses, capacitors, reclosers, voltage regulators, and conductors-for both rural and urban installations. These failure rates are in reality best estimates of the actual failure rates of the components. A range of deviations about these best estimates can be assessed at various confidence levels. Only transformers were found to exhibit a significant difference in failure rate between rural and urban installations. The component failures contributed about 15% of the total number of sustained outages for the OH feeders of this study. The remaining 85% of the sustained outages were due to external factors (75%) and loss of supply (10%). This suggests that an overhead distribution system is relatively insensitive to component failures, at the existing component failure rate levels