An 11.4-kV three-phase four-wire distribution system is capable of economically enhancing the supply power by using most of the existing 6.6-kV distribution system facilities. In this paper, the authors made a study on securing safety and quality in the 11.4-kV system by presupposing the use of a single resistance grounded neutral system based on EMTP simulations.
For the safety aspect, we conducted a study on the application to the 11.4-kV system regarding the OCR and the DGR. As a result, the conditions for the application to the 11.4-kV system were revealed, such as setting up a switch with an overcurrent relay on the distribution line as a measure for extending the OCR protected zone, and the most optimum neutral grounding resistance value for secure earth-fault protection. For the electric power quality aspect, we propose the load connection phase control method and the Y-A wiring for the transformers for motors as measures for controlling the voltage unbalance. Through these measures it becomes possible to secure the quality similar to that of the existing 6.6-kV system.
It is concluded that the basic technology has been established for a practical application regarding the protection scheme and the measures for keeping the voltage balance.
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