Purpose -The purpose of this paper is to pursue two following main goals: first, theorizing a new concept named as equivalent bus load in order to make a promising simplification over power system analysis. Second, proposing an outstanding fast and simple approach based on introduced concept for voltage estimation after multiple component outages while satisfying required accuracy. Design/methodology/approach -Equivalent load bus theory introduces three transfer matrices that describe power system topology. Mentioned matrices could be calculated simply after system reconfiguration without matrix inversion. Using transfer matrices a large-scale power system can be modeled by a simple two-bus power system from the viewpoint of any desired bus so that load flow calculation leads to same value. The analysis of simplified power system yields to extract a new incremental model based on equivalent bus load theory that will be distinguished as an outstanding fast method for voltage estimation aim. Findings -A deep study for fast voltage estimation aim is dedicated to evaluate proposed method from the accuracy and quickness point of view and the outcomes are compared to a well-known method as Distribution Factors (DF). Results and computational times unveil that presented approach is more accurate and much faster. Originality/value -A novel and new fast voltage estimation method for assessment of power system component outages is introduced. present, he has been with the Department of Electrical Engineering of the Amirkabir University of Technology, where he is now a Professor. His main fields of research are high voltage, electrical insulation, power system transient, lightning protection, and pulse power technology. He has authored and coauthored more than 300 papers and six books on high-voltage engineering and power system. Professor Behrooz Vahidi is the corresponding author and can be contacted at: vahidi@aut.ac.ir Sajjad Abedi received the BS Degree in Electrical engineering from the Isfahan University of Technology (IUT), Isfahan, Iran, in 2008, and the MS Degree (with honors) in Electrical Engineering, majoring in electrical energy management, from the Amirkabir University of Technology (AUT), Tehran, Iran, in 2011. Presently, he is a Graduate Research and Teaching Assistant in Electrical Engineering Department at AUT. He currently leads a number of research projects related to power system planning and economics, stochastic optimization, renewable energy integration, as well as smart grids development and deployment.Dr Hassan Rastegar received the BSc, MSc, and PhD Degrees in Electrical Engineering from the Amirkabir University of Technology, Tehran, Iran, in 1987, 1989, and 1998 Currently, he is an Associate Professor at the Amirkabir University of Technology. He has published many papers in journals and conferences. His research interests include power system control, application of computational intelligence in power systems, simulation and analysis of power systems, and renewable energy.