ABSTRACT
The great majority of service interruptions the customer sees are caused by problems on the distribution system. The overhead system is primarily affected by meteorological conditions such as wind and lightning whereas the underground system, while it sees fewer outages, is particularly concerned with service restoration time following a failure. While much of the decision is based on load density, availability of right-of-way, losses and substation placement, a major item which must be considered is reliability. Reliability of a distribution system is really evaluated in terms of outage rate and outage duration. It is defined as "the probability of a device performing its purpose adequately for the period of time intended under the operating conditions encountered". It is an interesting paradox that when utilities are asked what is the most important advantage of distribution automation they answer reliability, while they also generally agree that their customers will not pay more for better reliability.
