Improvement of the third harmonic based stator ground fault protection for high resistance grounded synchronous generators

Abstract

This paper shows a comparison and a proposed improvement of three different approaches based on the measurements of the third harmonic of voltage which are aimed to obtain a 100% protection of the stator winding in the case of ground faults in high resistance grounded synchronous generators. These three different methods are based in voltage measurements at the neutral and terminal connections, and also in the ratio of these measurements. From the results obtained in a real synchronous generator there are advantages of the scheme based on the ratio of the voltages measured at terminals and neutral, in the case of using the voltage threshold strategy. However, by using the proposed alarm-trip logic, remarkable improvements could be obtained in the case of detecting high impedance ground faults. Finally, this work may help to develop useful protective devices which detect ground faults at the synchronous generator stator windings. Although a first fault normally does not cause any problem, this have to be removed before the occurrence of a second ground fault which could cause severe machine damages and the consequent outage.

Keywords

• 100 % stator ground fault protection
• synchronous generator
• third harmonic
• phase-ground fault