1 A GA based methodology for improving real-time voltage profile for large power grids. Marcos Leone-Filho, IEEE Member Takaaki Ohishi Abstract—This paper describes a methodology for improving voltage profile for power transmission systems. Basically, it consists in tuning the transformers’ taps in a way that the buses voltages in the same area would stay around the same level. This approach was built focusing Brazil’s national integrated power system which is extremely regulated and centralized. This methodology uses a Genetic Algorithm (GA) with integer representation to search for taps sets that would lead the buses’ voltages to a desired level (generally 1p.u.). This new research was first validated with IEEE 30 buses and IEEE 118 buses test cases and then, tuned to deal with large interconnected power grids. The results showed that the proposed methodology was able to achieve its goal in getting voltages closer to the desired value. Index Terms—Power flow, Transformer Taps, Power Grid, Security, Real-time Operation. I. I NTRODUCTION T HERE has been a lot of talk lately about renewable energy sources, smart energy metering and smart power grids. However, there is no common sense among researchers on how to put all these upcoming technology together with the increasing demand for energy (like those pulled by electric vehicles). In countries like Brazil, this issue is even worse because the aging of its power grid and the lack of proper investment is challenging not only researchers but also gov- ernment entities to cope with this new scenario. In this context, many researches have been developed to provide solutions to improve system’s stability and to lower its costs. Also, many very interesting studies have been carried out in the field of Power Grid Transmission and, some of them try to deal with the grid stability using many different approaches (a widespread reference is the book of Kundur [1]), however most recent studies are more concerned about reducing transmission costs through capacitors allocation [2] [3] or through taps setting [4] [5]. On the other hand there is still some researches concerning real-time operations [6] [7] [8], but there is still not much work on improving system’s security through optimal tap setting for real-time operations, specially when it comes to dealing with large interconnected systems. M. Leone-Filho and T. Ohishi are with the Department of Systems Engineering at the Electrical and Computer Engineering Faculty in the State University of Campinas, Brazil. This work was partially supported by the Research Foundation of the State of S˜ ao Paulo (FAPESP), by the Brazilian National Research Council (CNPq) and by the Electric Power Transmission Company of the State of S˜ ao Paulo (“Companhia de Transmiss˜ ao de Energia El´ etrica Paulista” – CTEEP) In this sense, this paper tries to investigate the effect of tuning the transformers’ taps (more specifically for “load- tap-changing taps”) as a measure of controlling the system’s voltage profile. It is also important to state that tunning the transformers’ taps is one of the ways a power grid operator is able to control the voltage transforming ratio and therefore, controlling buses’ voltages. Hence, more specifically, this study investigated the effectiveness of tuning all taps (the decision variables) in a transmission grid in order to achieve a better voltage profile (objective function) for the whole grid. Some similar papers [9] have been published, but none of them focused on improving the voltage profile with the same methodology presented in this paper nor has anyone proposed such study for large-scale-highly-interconnected power grids. As soon as it is agreed among researchers and engineers that a desired state of the power grid is the one that every single bus voltage would stay around the level of 1p.u., this work proposes a methodology which objective is to stabilize the grid voltage profile around 1p.u.. Hence, this paper will show the basis of this methodology (section II), how it was implemented (section III), the results achieved from the tests cases (section IV) and the conclusions that the authors were able infer from the tests results (section V). II. METHODOLOGY BASIS Since buses’ voltages are sensitive to transformers’ taps changing, it was created an algorithm that aims to explore different combinations of taps (the decision variable) through the network in order to find a specific set of taps that would improve the overall grid voltage profile. Hence, for each set of taps setting, it is necessary to deter- mine the corresponding electric system state, that is obtained through the resolution of the following load flow Equations [10]: P km =(t km V k ) 2 g km − (t km V k )V m g km cos (θ km )+ −(t km V k )V m b km sin (θ km ), {k,m} =1, ..., N B (1) Q km = −(t km V k ) 2 b km +(t km V k )V m b km cos (θ km )+ −(t km V k )V m g km sin (θ km ), {k,m} =1, ..., N B (2) Where NB is the number of buses in the power system, km represents a branch where k is the original bus and m is 978-1-4673-2673-5/12/$31.00 2012 IEEE