Islanding Protection Equipment for Synchronous Generator Interconnected to Distribution Line

In recent years, enhancement of consciousness for energy saving and problem of environment are widely encouraging the installation of dispersed storage and generation (DSG) units such as co-generation and photo-voltaic generation. When a distribution line with the DSG is disconnected from the main source of utility, the DSG supplies power to the distribution line. The situation, namely islanding, creates various problems for the reliable and safe operation of the distribution line. Thus, the islanding must be immediately prevented by islanding protection equipment. This paper describes an islanding protection scheme and the digital protection equipment for a synchronous generator. The proposed scheme detects an islanding of a synchronous generator from frequency fluctuation occurred by feeding a sinusoidal small reference voltage signal into the auto voltage regulator circuit of the generator. The authors have manufactured the digital protection equipment applying the scheme, confirmed the excellent performance by testing in an artificial distribution line. In the paper, a determining proceeding of the setting value of the equipment is described.