This paper describes a technique for evaluating reliability of a composite distribution system having Distribution Generator (DG) sets. The capacity of a composite distribution system includes capacity of a distribution substation and distribution generator sets. The capacity of a distribution substation has been assumed to be a continuous random variable whereas Markov modeling has been adopted for checking availability of DG sets. Extreme minimum and maximum distributions have been used for capacity and load on the distribution system. Therefore, it is worst case reliability evaluation of the composite distribution system. Probability of failure of the composite distribution supply system has been evaluated using Monte Carlo simulation. A case study has been considered for explaining the developed algorithm.

For many years, distribution systems have been designed to deliver electrical energy to consumers without any generation of these systems. The demand of the consumers was being fulfilled with the help of distribution substations. However, due to major changes in the legislative framework of the electric sector and the move towards liberalization of the electricity markets, generating units were introduced in the distribution systems. These units are of limited size (100 MVA or less) and are connected directly to the distribution network or the consumer sites. These units are usually customer owned and controlled, and are referred as Distribution Generators (DGs). The main reasons behind the expected widespread use of DG sets are: (1) Deregulation in the power market, which encourages public investment to sustain the development in power demand; (2) Emergence of new generation techniques with small rating, ecological benefits and increased profitability; and (3) Limitations of existing networks/sources with the continuous growth of load (Ackerman et al., 2001; and Hegazy et al., 2003).

The advantages associated with inclusion of DG sets are: (1) Improvement in voltage profile; (2) Reduction in power loss; (3) Release of system capacity; and (4) Improvement in composite system reliability. Further, there are associated problems with such composite distribution systems, e.g., operation and control of the different types of DG sets. Many researchers have attempted the issue of generating capacity reliability evaluation but very limited efforts have been made in reliability evaluation of capacity of a composite distribution system (Billinton and Allan, 1998; Kim and Singh, 1998; Rias et al., 1998; and Allan and Billinton, 2000).

This paper addresses the problem of capacity reliability evaluation of a composite distribution system with customer-owned DG sets when the location of DG sets is known to the utility. Further, in this paper limitations of the distribution network have not been considered. Monte Carlo simulation along with extreme distributions for load and capacity have been considered so as to obtain the worst case reliability evaluation.

Electrical and Electronics Engineering Journal, Distribution Systems, Probability Distributions, Adequacy Assessment, Monte Carlo Simulation, Cumulative Distribution Function, Failure Probability, Composite Distribution Supply System, Distribution Substation, Electric Sectors, Electricity Markets.