Application of diesel generation at Hawaiian electric substations for power system support

Hawaiian Electric Company (HECO) is applying distributed generation to help satisfy growing peak system loads on the Island of Oahu until a new bulk power plant is operational in the 2009 timeframe. This paper discusses the interconnection issues associated with applying 4.92 MW diesel engine-based distributed generation plants at several substations for bulk system support. From a DG perspective these are large units installed at relatively small substations, so there are several issues of concern including the impact of generator fault current contributions, ground fault overvoltage issues on the 46 kV transmission lines feeding the substations, the potential for islanding, the possibility for ferroresonance, stability issues, and the generator´s impact on distribution system voltage regulation. A study of these issues was performed to identify any problems and solutions to allow for successful system generator integration. The study showed that the units could be successfully applied, however, significant modifications to the HECO protective relaying, the station load tap changer settings, and use of carefully coordinated settings of the DG protection were necessary to avoid several identified potential problems. The distributed generation plants were commissioned in the fall and winter of 2005 and have been successfully operated for system support. The project serves as an example of how DG can be used for power system support, but also highlights the care that must be exercised in any large scale DG interconnection of this type