Islanding Scheme Design for Generators and Assessment of Impact of RGMO on Frequency Stability of Island

Abstract

Transmission system forms the backbone of any electrical power system. Transmission systems are exposed to environment and prone to fault. Therefore, chances of unwanted event resulting in large scale blackouts can never be ruled out. Renewable integration has increased the vulnerability of power system. Therefore, over the year resilience is gaining more and more importance for power system planners. Many grid codes have implicit provision of resilience. Key features of a resilient power system are robust islanding scheme and adequate number of black start resources. When a large power system fails to operate in synchronism, it becomes preferable to create small islands as the surviving islands make the restoration process fast. Success of an islanding scheme depends on the design as well as implementation of the logic. Logic needs to be robust as well as simple. Extensive study is required to design an effective islanding scheme. For islanding scheme design various preliminary studies are done and the results are discussed in the paper. The purpose of the studies was solely to check the frequency stability of the island. These islanding logic needs to be designed purely based on frequency logic and no under voltage logic to be used. This is because these islands are designed for supply of capital city, only in case of total or partial grid failure. Therefore, here island scheme design only aims at arriving frequency setting and load shedding scheme design inside the island. However, these studies are done based on certain assumption which will also be discussed in the paper. Its purpose is to check the broader feasibility of an islanding scheme. The final islanding logic may be finalized by the respective generating plants in consultation with their OEMs. The governor of a generating unit has a vital role to play in the success of the islanding. Currently in Indian power system restricted governor mode of operation (RGMO) is in service for generators [1]. In this paper the impact of RGMO on island frequency stability is also studied.