Excitation system protective limiters and their effect on volt/var control- Design, computer modeling, and field testing

The action of excitation system protective limiters and var regulation are often not taken into account in planning studies, and actual units may be q uite different than simulations. This may lead to incorrect predictions of actual stability limitations, or even voltage collapse phenomena, The desig n of the excitation system protective limiters such as Over Excitation Limi ters (OEL), Under Excitation Limiters (UEL) and Volts/Hertz (V/Hz) is expla ined, and models presented, For system events where these controls and limi ters may become active, modeling in transient stability studies is importan t to correctly predict volt/var performance. Specific models applicable to the GE EX2000 digital-based control systems are shown for reference, althou gh the general concepts discussed here are applicable to any other excitati on equipment, An important aspect of the new digital-based excitation contr ols is that they allow for more intelligent limiter functions and protectiv e features not convenient with older equipment, Test procedures and results are shown to illustrate the limiter performance.