COLD LOAD PICKUP IN POWER DISTRIBUTION SYSTEMS WITH LOCAL GENERATION

Abstract

Most of the customer outages are the results of some problems related to distribution systems .Prolonged outages may cause cold load pick up (CLPU) problems because of increased penetration of thermostatically controlled devices and the loss of diversity among these devices. Since loads higher than normal may be expected after a prolonged outage or scheduled cuts, restoration problems may occur when there is no enough reserve capacity in the substation. The main objective associated with CLPU condition is to restore the network smoothly and quickly in the post outage period. CLPU condition has two phases namely inrush phase and enduring phase. Special attention has been given for the inrush phase of the CLPU condition in the present thesis work. Inrush currents are mainly encountered due to switching operations. Inrush currents comparable to that of short circuit currents will result in high mechanical forces that will deteriorate transformer windings, insulation and other supporting structure. So an algorithm is been presented to estimate the probability of danger of deterioration of windings, and to estimate loss of life due to switching operations for different remanent flux values with the help of transformer design parameters. In the present thesis work restoration of the network in single step under CLPU conditions has been taken as the main objective in order to reduce the load demand during CLPU, to increase the system reliability and also to supply a part of the network during outage. For this purpose distributed generators (DG) are been used. The location and capacity of DG to be placed has been decided keeping in view that the cost involved should be minimum and returns due to DG placement in the network should be maximum. Also DG placement has to be such that the switching operations of distribution transformers are minimized there by reducing loss of life of the transformers. For this purpose genetic algorithms are been used to decide the DG location and Forward/backward sweep load flow algorithm has been used to decide the capacity of DG to be placed. A 33-bus, 12.66KV system is considered for the entire analysis. Aluminum wound distribution transformers are considered for study.