Generator excitation systems-performance specification to meet interconnection requirements

The purpose of the excitation system is to supply the synchronous machine field current to regulate either terminal voltage or VAr/PF to setpoint. The excitation system also contains protective limiters that protect the machine from operating outside its capability in either underexcited, overexcited, stator current, or V/Hz. The main focus of this paper is to address the proliferation of system interconnection requirements, that are in many cases tailored to specific projects, that have led to a need for better processes for specification of excitation control systems. The guidelines in IEEE Standards 421 serve to provide a framework for these specifications, but specific case studies are often needed to determine final excitation system specifications. The traditional role of the excitation system in regulating generator voltage and thereby helping to control system voltage allows for significant latitude in design and tuning to affect performance. The two key factors discussed are transient gain and ceiling forcing.