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In distribution systems with large residential load, thermostatically controlled devices contribute major portion of total load. Restoration of such systems after prolonged interruption may create a load significantly higher than the normal load. This condition is called cold load pickup (CLPU). The enduring component of CLPU may cause severe voltage drops along the feeders and transformer heating, thus making the system restoration difficult. This paper discusses an approach to include restoration under CPLU conditions in distribution system planning and expansion. The approach can be applied to determine the most optimal transformer size and feeder sizes while ensuring the minimal restoration time and acceptable voltages and transformer heating during CLPU conditions. The aim is to develop a tool that can be used in conjunction with the overall distribution system design to ensure quality power even in emergency conditions while minimizing the cost.
Date of Publication: May 2004