AN ANALYTICAL APPROACH FOR STEP-BY-STEP RESTORATION OF DISTRIBUTION-SYSTEMS FOLLOWING EXTENDED OUTAGES

Loss of diversity among loads may cause cold load pickup problems afte r an extended outage in distribution systems. Thermostatically-control led devices such as air-conditioners, heaters, heat pumps, water heate rs etc. become the largest portion of load during restoration. In this paper, an analytical approach for restoration of distribution systems during cold load pickup is presented. A delayed exponential model is used to represent the load during cold load pickup. A thermodynamic mo del of transformers is used to determine the loading limits for this t ype of load. Whenever loading limits are reached, sections are restore d step-by-step. In step-by-step restoration, the sequence of sections restored plays an important role in total restoration time. An optimal restoration sequence of different sections of the distribution system is determined for minimum total restoration time as well as minimum c ustomer interruption duration.