ISSN (Online) 2321 – 2004 ISSN (Print) 2321 – 5526 INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN ELECTRICAL, ELECTRONICS, INSTRUMENTATION AND CONTROL ENGINEERING Vol. 2, Issue 6, June 2014 Copyright to IJIREEICE www.ijireeice.com 1603 Computation of Sensitive Node for IEEE- 14 Bus system Subjected to Load Variation P.R. Sharma 1 , Rajesh Kr.Ahuja 2 , Shakti Vashisth 3 , Vaibhav Hudda 4 Department of Electrical Engineering, YMCAUST, Faridabad 1, 2, 3 Department of Electrical Engineering, AKGEC, Gaziabad 4 Abstract: The load flow analysis is an important method for the power system analysis and designing. This analysis is carried out at each and every state of planning, operation, control and economic scheduling. In this paper, we have focus on the finding of most sensitive node in IEEE- 14 bus systems. Simulation is carried out at PSAT Matlab Toolbox which includes a complete set of user-friendly graphical interface and a Simulink-based editor for one-line network diagrams which utilizes the L-index method and FVSI for voltage stability analysis and sensitive nodes determination. In this project, firstly we have analyzed IEEE- 14 bus system under the standard test data & after that we have increased load data in step of 5%. For finding a most sensitive node, the results are compared with the original power flow results of IEEE- 14 bus system. Keywords: IEEE-14 Bus, System, Sensitive Node, Reactive Power, PSA I. INTRODUCTION The voltage stability is the capability of a power system to maintain steady state voltage at all buses in the system at normal values and after being subjected to a disturbance [1]. A power system becomes unstable, when voltages uncontrollably changes due to the disbalance between load and generation, outage of equipment & lines and failure of voltage control mechanism in the system. The problem of voltage instability occurs mainly due to deficient supply of the reactive power or by an unnecessary absorption of reactive power[2]. Continuous monitoring of the system status is required because the voltage instability affects the satisfactory operation of power system. Stability of the power systems can be identified through various stability factors. The slow variation in reactive power loading towards its maximum point causes the conventional load flow solution to attain its non convergence point. The ordinary load flow solution does not converge, beyond this point i.e. it forces the system to reach the voltage stability limit prior to bifurcation in the system [3]. The margin calculated from the base case solution to the maximum convergence point in the load flow calculation determines the loadability maximum at a particular bus in the system. Thus in this system we examined IEEE- 14 system by increasing its reactive loading by 5%, 10%, 15%, 20%, 25%, 30%, 35% and till 40%. II. METHODS OF FINDING OUT WEAKEST BUS The Indian electrical infrastructure was generally considered unreliable. It is essential to locate a sensitive node in the power system in order to avoid the severe disturbances. The critical bus is determined by finding out the maximum acceptable load on the bus. The most critical bus in the system is the bus which can accept smallest maximum load. Line stability index method, Fast Voltage Stability Index (FVSI) and Voltage Collapse Prediction Index (VCPI) are some most important methods which are used to finding out the most sensitive line in the power system [4]. III. INDEX FORMULATION LSI and FVSI index formulation is discussed here in this subsection as following: A. Line Stability Index Formulation Based on the transmission concept in a single line M. Moghavvemi’s derived a line stability index to find the voltage of an interconnected system in a reduced single line network [4]. In this formulation the discriminator of the voltage quadratic equation is set to be greater or equal than zero to maintain stability. A typical single transmission line where index is derived from is illustrated in Fig. 1: Fig. 1. Single line diagram of a transmission line in the power system Where, Vs∠δs, Vr∠δr are the sending end and receiving end voltages. R+jX is the impedance of the transmission line P+jQ is the receiving end apparent power θ is the line impedance angle δ is the angle difference between the supply voltage and the receiving end voltage. The line stability index is expressed by Lmn, proposed by Moghavvemi and Omar (1998) is formulated based on a power transmission concept in a single line. The line stability index Lmn is given by [5], Vs∠δs R+jX P+jQ Vr∠δr