Abstract—In power system protection, the need to know the load current together with the fault level detected by a relay is important. This is due to the fact that the relay is required to isolate the equipment being protected if a fault is present and keep the breaker associated with it closed if the current level is lower than the maximum load level. This is not an issue for a radial system. This is not the same however in a looped power system. In a looped power system, the isolation of an equipment system will contribute to a topology change. The change in the power system topology will then influence or change the maximum load current and the fault level detected by each relay. In this paper, a method of data collection for changing topology using Matlab and Sim-power will be presented. The method will take into consideration the change in topology and collect data for each possible topology. Keywords—Topology Change, Power System Protection, Power System simulation, Matlab, Sim-power. I. INTRODUCTION HE need to know the load current and the minimum fault current that flows through a relay is important in setting the relay. Studies have been made by past researchers that require this information [1], [2]. In a radial system, this is not an issue due to the fact that the current can only flow in one direction and the problem of topology change does not occur. This is not the same however for a looped power system where the current can flow in both directions through a relay and topology change can take place [3]. In an event of a topology change, the maximum load current and the minimum fault current that is detected by the relays in the system will change [4]. This will cause coordination problems for the relays in the system. In this paper, using Matlab and Simulink, a data collection algorithm for power systems with changing topology will be presented. The algorithm will automatically change the topology, run a steady state analysis and store the current value of the relay for every possible topology that the system could have. II. ALGORITHM In this paper, the change in topology will be viewed as isolation of lines. If a system has a number of lines, then Aidil Azwin is a senior lecturer in the Department of Electrical Engineering of University Tenaga Nasional (e-mail: aidilazwin@ uniten.edu.my). Farrukh Hafiz Nagi is an associate professor in the Department of Mechanical Engineering of University Tenaga Nasional. Agileswari K. Ramasamy is an associate professor in the Department of Electrical Engineering of University Tenaga Nasional. Izham Zainal Abidin is an associate professor in the Post Graduate Studies College for Universiti Tenaga Nasional. isolating one or more of the lines will be considered changing the topology of the system. The algorithm for this paper is shown below: 1. Identify the lines which exist in the system. 2. Identify breakers associated with each line in the system. 3. Identify the maximum number of lines than can be isolated in the system.(N) 4. Initialize i=1 5. Identify the possible isolation combination that could be done in the system for I lines isolated (M). 6. Initialize j=1 7. Perform isolation for combination j. 8. Perform steady state analysis for the system intact 9. Keep the data obtained in (8) in a structure for each relay. 10. Normalize the system such that all the lines are intact. 11. Increment j. If j>M, increment I, if i<N repeat starting from (5) if not terminate process. If j<M then repeat starting from (7). The first step in the algorithm will have to be done manually. This is done by naming all the lines in the Simulink diagram. The second step is also done manually; the best practice is to have the names of the breakers in some way associated with the names of the lines connected to it. The 3 rd step depends on how large the system is. The more lines available, the more the number of lines can be isolated in order to provide power to the load. This can be explained using an example. If a system has 5 lines, then isolating 4 lines would be pointless because the one line will not be of use in transferring power to a load from a source. In 5, the procedure is done using the nchoosek command in Matlab. The nchoosek command will list down all the possible combinations of choosing k elements out of the N elements in a set where N is the total elements in the set. In this command k is an integer given by the user. The flowchart for performing step 7 is shown in Fig. 1 Aidil Azwin Zainul Abidin, Farrukh Hafiz Nagi, Agileswari K. Ramasamy, and Izham Zainal Abidin Steady State Simulation of Power Systems with Change in Topology T World Academy of Science, Engineering and Technology International Journal of Electrical and Computer Engineering Vol:7, No:8, 2013 1046 International Scholarly and Scientific Research & Innovation 7(8) 2013 scholar.waset.org/1307-6892/16138 International Science Index, Electrical and Computer Engineering Vol:7, No:8, 2013 waset.org/Publication/16138