International Journal of Multidisciplinary Research and Modern Education (IJMRME) ISSN (Online): 2454 - 6119 (www.rdmodernresearch.org) Volume I, Issue I, 2015 146 UNSYMMETRICAL FAULT ANALYSIS & PROTECTION OF THE EXISTING POWER SYSTEM R. S. Meena* & M. K. Lodha** Department of Electrical Engineering, Sri Balaji College of Engineering & Technology, Jaipur, Rajasthan Rajasthan Technical University Kota Abstract: Now a day’s electrical power system is in the process to convert in smart power system with interconnected national and regional grids. Modeling of power system has become a necessary in order to make right decision, check for any potential problems, and fault conditions in large interconnected network. In this paper we shell deal with unsymmetrical faults in a proposed network. In recent year power system engineers shifted protection method from classical methods to digital or numerical protection techniques, in this technique high crunching capability, which has made it possible to design digital filters in real time protection system with smart technologies. Multifunctional relay also installed in modern power system network for protection of transmission line, generator protection, motor protection, real time fault location, protection of busbar and other important equipments. This paper is devoted to abnormal system behaviour under conditions of unsymmetrical fault in power system networks using MATLAB Simulation Techniques. Key Words: Modern Power System, Unsymmetrical Fault, Generator Protection, Interconnected Network, Digital/ Numerical Protection. I. Introduction: In the modern large interconnected power system, heavy currents flowing during a fault must be interrupted much before the steady state conditions are established. This paper is devoted to abnormal system behaviour under conditions of unsymmetrical fault in power system networks. Various types of unsymmetrical faults that occur in power system- (a) Shunt type fault (b) Series type fault (a) Shunt Type Fault: In shunt type fault also three category- (i) Single-Line to Ground Fault (ii) Line-to-Line Fault (iii) Double -Line to ground Fault (i) Single line to ground fault: in this type of fault at the fault point , the currents out of the power system and the line to line ground voltages are constrained as follows:- Ib= Ic = 0 Va = Z f Ia The symmetrical components of the fault current are Ia1= Ia2 = Ia0 = 1/3Ia Va1+Va2+Va0 = ZfIa1 (ii) Line to line fault: line to line fault at any point in a power system then the currents and voltages at the fault can be expressed as- Ia= 0, Ib = -Ic Vb-Vc = IbZ f (iii) Double line to ground fault: For this condition the currents and voltages at the fault are expressed- Ia=0, Ia1+Ia2+Ia0 =0 Vb =Vc = Z f (Ib+Ic) = 3Z f Ia0