Over-Frequency Mitigation Using Coordinated Generator Shedding Scheme in a Low Inertia Power System

The objective of this paper is to mitigate overfrequency problem of a low inertia power system using coordinated Over-Frequency Generator Shedding (OFGS) scheme. Recently, prolific amount of wind resources has been introduced in many power systems around the world. These variable speed wind power plants cannot contribute to system inertia unlike traditional synchronous generators. This leads to insufficient system inertia and the system can be termed as low inertia power system. If an area is transporting significant amount of power to adjacent area, then tripping of interconnection line can cause excess power thus to increase the system frequency in that area. This research work proposes a method to mitigate this problem using overfrequency generator tripping scheme. Results show that tripping wind turbine generator provides the best system response if single generator tripping scheme is undertaken. In case of double generator tripping scheme, wind-hydro combination tripping demonstrates the lowest frequency summit, lower Rate of Change of Frequency (ROCOF) and faster settling time. Finally, generators having different inertia constants are tripped to portray that generators having lower inertia constant should be tripped first.

1. Introduction

Interconnected multi-area power system has become inescapable with the increase in size and capacity of modern power system. The interconnectivity and complicacy in modern power system can enhance the risk of over-frequency problem in a power grid [1]. Especially, when an area is sending large amount of power to its adjacent area, an interconnection trip can cause an undesirable over-frequency situation in that area. Because of loss of load, the excessive power, which was previously being sent to its neighboring area, can cause over-voltage and over-frequency problem. The severity of these problems depends on overall system configuration, system inertia and type of generator turbines available on that system.