Discriminating Method of Islanding for Dispersed Non-utility Generator Interconnected to High-voltage System

Abstract

In recent years, dispersed-generator such as co-generation facilities or solar battery and the like become increasingly popular. From the viewpoint of energy effective and electric power demand for stable secure, the dump power from the system interconnection is expected to use positively. But in case of interconnecting dispersed-generator to the commercial system of the electric company, two problems will occur when operating in isolation with the other general consumers. One is of the power quality for the general consumers. And the other one is of the security problem caused by charging a part of commercial system line that has to be no voltage.
For the reason above, the transfer tripping system is necessary for preventing from the islanding in case of interconnecting dispersed-generator, comparatively large co-generation system (2, 000kW or more) and the like, to high-voltage system. However, the transfer tripping system that there are some switches in the transmisson line needs many equipments and comunication lines to collect switches' information, because it detects the islanding from the “on-off” information of all switches.
Therefor, we develop new system that the voltage difference between the commercial system side and dispersed-generator side detects isolated operating without switches' information.
For the realization of this system, we study the operating principle of the digital relay that detects accuracy the differential phase angle and the differntial frequency between two power sources of the different frequency after cutting off the interconnection.
In addition we present the example of the application to 66kV loop service system.