An Enhanced Load Transfer Scheme for Power Distribution Systems Connected with Distributed Generation Sources Wen-Chih Yang Department of Electrical Engineering Technology and Science Institute of Northern Taiwan No. 2, Xueyuan Rd., Peitou, Taipei TAIWAN, R.O.C. wcyang@tsint.edu.tw Wei-Tzer Huang Department of Electrical Engineering Chienkuo Technology University No. 1, Chieh Shou N. rd., Changhua City TAIWAN, R.O.C. vichuang@ctu.edu.tw Abstract: - This paper presents an enhanced load transfer scheme for power distribution systems connected with distributed generation sources. Load transfer is an important approach to improve the reliability of power distribution systems. The proposed load transfer scheme takes into account the effects of distributed generation sources on power distribution systems. Hence, it is more useful than conventional load transfer scheme. In this paper, the procedures of conventional and proposed load transfer scheme are addressed in detail. Two example systems for computer simulation were constructed and several simulation scenarios were carried out by this work. Simulation results shown in this paper clearly indicate the troubles of conventional load transfer scheme and the practicability of the proposed load transfer scheme. Key-Words: - Load transfer, Distribution system, Distribution feeder, Distributed generation source, Interconnection. 1 Introduction Load transfer is an important approach to improve the reliability of power distribution systems [1-6]. For a power distribution system, equipment fault or maintenance will result in the interruption of electric service. Customers may suffer great losses of safety and/or money during interruption of electric service. In order to shorten the duration of interruption of electric service, transferring the loads of the faulted distribution feeder to health distribution feeders as soon as possible is an important task for utilities [7- 9]. For a power distribution system without distributed generation sources (DGSs), the load transfer scheme is very simple. Once a fault happens to a distribution feeder, power engineers can transfer the loads of the faulted distribution feeder to supported distribution feeders via switchgears if the faulted area has been isolated. The major consideration of conventional load transfer is that the currents of supported distribution feeders must be lower than their thermal limits after load transfer. Nowadays, more and more DGSs are operated with power distribution systems in parallel for reducing CO 2 emission and greenhouse effect [10-13]. DGSs, such as photovoltaic arrays, wind turbines, hydro generators and cogeneration systems are all generating facilities [14-19]. They can generate electric power into the distribution feeders connected and change their operating states [20-23]. When a fault happens to a distribution feeder which connects with DGSs, the DGSs together with the loads of the faulted distribution feeder will be transferred to supported distribution feeders. Under this circumstance, the operating states of supported feeders will be affected by the DGSs. If the effects are too large, security of the power distribution systems and customers are injured [5,6]. Because WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Wen-Chih Yang, Wei-Tzer Huang ISSN: 1109-2734 136 Issue 4, Volume 10, April 2011