STEADY STATE ANALYSIS OF REDUCED INDIAN POWER SYSTEM

Abstract

Due to ever increasing demand of electrical power along with penetration of renewable energy sources, a proper analysis have to be carried out to determine the effect of increased power transactions through existing transmission network. Although, analysis of power flow of the full model of a power system is preferable in terms of accuracy, it is impractical owing to the large amount of memory, computational complexity and cost involved. As a result, one has to look for an equivalent reduced model which reflects the original system conditions as accurately as possible. The very idea of obtaining a reduced system is to obtain a miniaturized version of the actual system in order to retrieve specific information which should be as accurate as possible in comparison to the information obtained by the actual system. Also, an accurate reduced model decreases the computational complexity, large memory, cost and time associated with the detailed analysis carried out on original network. In literature, there are various types of reduced equivalents available, owing to different circumstances like reactive-active power management, power system calculations, market-pricing etc. The main objective of this article is determination of a reduced model which can be used to represent either the steady state power transactions at the transmission level between different zones (comprising of aggregated generations and loads) or power transactions through critical lines which in turn can be utilized for system planning and market simulations. This dissertation report involves the implementation of one of the early network reduction technique known Ward’s network equivalent and a recent method based on PTDF. Out of these two, the network reduction as per Ward’s method focuses on partitioning a large system into three zones as: the zone which retains selected network lines in the reduced model (internal zone), the zone which is of no interest (external zone) and a boundary zone connecting the two before-mentioned zones. This method is suitable only when all the systems of interest are confined in a single area. But for market studies, specific systems can be located anywhere in the actual model and this entails one to adopt means of network reduction based on PTDF (power transfer distribution factors). The method based on PTDF makes use of a dc-flow model. The dc-flow model comprises of linear systems only and thus computational time and memory required are much less as compared to the ac-flow models, which comprise of non-linear system due to which iterative solution has to be conducted. A PTDF matrix acts as the link between powers injected at different locations to the power flowing in different transmission lines and as a result of this, more accurate reduced network equivalents are obtained by reduction of the PTDF matrix. However, models based on PTDF (based on approximations of DC-power flow), because of converting an empirical problem into linear one, yields a linear solution. Difference exists between the empirical solution and the linear one (owing to the difference in problem-solving technique) and considering the practical scenarios, the empirical solutions are more accurate. In this report, steps have been taken to extend the method based on PTDF to yield more accurate power flows i.e. closer to an empirical solution. Finally, the ideas developed in this report are extended to obtain a reduced equivalent model of actual Indian Power System.