Improved high‐speed de‐excitation system for brushless synchronous machines tested on a 20 MVA hydro‐generator

Abstract

Synchronous machines with brushless excitation have the disadvantage that the field winding is not accessible for the de‐excitation of the machine. This means that, despite the proper operation of the protection system, the slow de‐excitation time constant may produce severe damage in the event of an internal short circuit. A high‐speed de‐excitation system for these machines was developed, and this study presents the continuation of a previously published study. This study presents the design by computer simulation and the results of the first commissioning of this de‐excitation system in a commercial 20 MVA hydro‐generator. The de‐excitation is achieved by inserting resistance in the field circuit, obtaining a dynamic response similar to that achieved in machines with static excitation. In this case, a non‐linear discharge resistor was used, making the dynamic response even better.