Generator Excitation System Replacement in Geothermal Power Stations – Merits and Pitfalls

Abstract

Some geothermal power stations exceed their projected operating life by adopting life-extension techniques. While some mechanical equipment in power station can readily exceed their design life, most of the control equipment need replacement due to obsolescence and difficulty getting technical support.
This paper presents the options available for the replacement of ageing excitation system, which is one of the major components that control the operation of turbine-generators. The performance requirements, functions and elements of modern excitation systems are discussed as an overview. The main drivers to proceed with replacement projects are elaborated with consideration of transmission system requirements, as well as long-term plans and objectives from generation companies. Technical issues and pitfalls in the retrofit design process need to be considered to avoid delays during installation work. The timeframe to complete the installation and wiring works is limited as these are done during scheduled plant outages. Issues that are specific to geothermal plant applications are deliberated with consideration of technologies currently available in the market. The upgrade work has to consider the interfaces between the excitation system and other equipment, such as control system DCS, electrical protection relays, dependable power supplies, measuring devices, and generator. Experiences on excitation replacements projects in geothermal power plants are shared to provide generation companies some guidance in doing similar retrofit projects.