Applications of ANFIS in Loss of Excitation Faults Detection in Hydro-Generators

1. Introduction

Synchronous machines suffer from a very common fault which is a Loss of Excitation (LOE) fault. It is usually can be caused by short circuit of the field winding, unpredicted field breaker open or Loss of Excitation (LOE) which triggers relay mal-operation. According to the statistics in China, the generator failure due to Loss of Excitation (LOE) accounts for 69.5% of all generator failures as discussed in(Weijian 2002; Shi 2010). Loss of Excitation (LOE) may originate severe damages to both generator and system. For the generator; when Loss of Excitation (LOE) happens, a slip occurs which may cause rotor over heating due to the slip frequency in rotor circuits. Also, as the synchronous machine runs as an induction machine after Loss of Excitation (LOE) conditions, large amount of reactive power supplied by stator current is required and the stator may suffer over heating due to this large current. On the other hand, for the system; its voltage drops after the generator loses its excitation, because the synchronous generator operates as an induction machine and absorbs reactive power from the system. For some weak system, the system voltage may collapse due to the Loss of Excitation (LOE) of an important synchronous generators discussed in (Elkington et al. 2008). Also, when a generator loses its excitation, other synchronous generators in the system will increase their reactive power output. This may represent a source of the overloading in some transmission lines or transformers and the over-current relay may consider this overloading as a fault and isolate the non-fault equipment as presented in (Benmouyal 2007; Kundur 1994; Paithankar and Bhide 2010; IEEE Std 2006; Blackburn and Domin 2014; Elmore 2003; Reimert 2005; Mozina et al. 2008; Patel et al. 2004; Ebrahimi and Ghorbani 2015). These above reasons motivate this research work to solve for this dilemma.