A New Protection Scheme for Stator Faults in Synchronous Generators Pouya Mahdavipour Vahdati ∗ , Arash Arjmandi ∗∗ , Heresh Seyedi ∗∗∗ , Soheil Moradi ∗∗∗∗ ∗ Iran University of Science and Technology, Tehran, Iran, pooyamahdavipour@gmail.com ∗∗ K.N.Toosi University, Tehran, Iran, a.arjmandi@ee.kntu.ac.ir ∗∗∗ University of Tabriz, Tabriz, Iran, hseyedi@tabrizu.ac.ir ∗∗∗∗ Shahid Madani University, Tabriz, Iran, soheilmoradi@yahoo.com Abstract A new voltage controlled overcurrent protection scheme is proposed which is a backup protection method for differential protection. This scheme which is realized by fuzzy controllers is considered to be mounted beside a differential protection system, which operates in the cases that differential protection is unable to detect the fault. This novel protection scheme operates by adjusting the plug setting of the overcurrent relay that sends the trip signal to three-phase breaker. In the proposed method fault occurrences can be deter- mined regardless of variations of voltage and current of terminal in different working states of synchronous generator. This is done by measuring other variables than those used in conventional protection methods. To demonstrate the proposed method, a synchronous generator with internal fault model is used. Numerical simulations validate the functionality of this novel scheme under different conditions. Keywords: Fault detection, Fuzzy logic, Synchronous generator, Internal fault, Backup protection 1. Introduction The most important element of a power system is the Synchronous Generator. As a result, many protec- tion methods are proposed to protect Synchronous gen- erators from different types of faults. About the pro- tection of the synchronous generators against various types of faults of several previous researches have been done. The authors in [1] presented a ”100% stator- ground protection” based on the third harmonic voltage at the neutral and terminal ends of the generator. Also a research for detecting the internal fault at the stator winding is represented [2], which uses artificial neural network for fault detection and fuzzy logic for sending the trip signal to the breakers. Using the artificial neural and fuzzy logic, results in inter-turn short circuit fault detection, fault type classification and the fault location identification in [3]. Different applications of the fuzzy logic are presented in several protection schemes which proves efficiency of the method. In designing a pro- tection scheme for the protection of synchronous gen- erators against various types of faults, the main part is the generator model that is used for study. The most complete analysis of the dynamic behavior of the syn- chronous generator is reached through Finite Element study. But because of the long simulation time that is needed for Finite Element studies, other models are proposed that can efficiently define the behaviors of the synchronous generator under fault conditions for short simulation times. Two of the most important represen- tations are the Direct-Phase representation and the Volt- age Behind Reactance (VBR) representation [4], [5]. A technique, used to implement the internal fault for mod- eling the synchronous generator, is provided in [6]. A partitioned winding direct-phase model, which is given in [7] and [8], is used for the protection scheme pro- posed in this paper instead of the partitioned winding (VBR) model, which is given in [9]. The reason is that in [7] and [9] the possible occurring faults are not lim- ited to symmetrical faults. A Backup Overcurrent Pro- tection scheme for the stator winding of a synchronous generator is proposed to operate in conditions that the main protection scheme, which is the high-speed differ- ential protection [11], is unable to detect the fault. In this protection scheme fuzzy logic is used as the final decision maker and sets the plug setting of the over- current relay that sends the trip signal to the breakers. This paper is organized as follows: In Section.2 the direct-phase representation of the synchronous gener- ator, with all the details, is given. In Section.3 the pro- 978-1-4673-5634-3/13/$31.00 ©2013 IEEE