The Effect of R/X Ratio of the Short Transmission Line on Transient Stability

Problem statement: The exact short transmission line model consists of the resistance and reactance. Most of previous researches study the transient stability of single machine infinite bus with neglecting the resistance of the line. Thus the simulation results may not close to the practical system. With the consideration with the actual short line model, it causes difficulty of deriving the mathematical model. Approach: This study investigates the transient stability of power system with consideration of the exact short transmission line model. The concept of two-port network is applied in this study. The generator, transformer and short transmission line are represented by a two-port. With the combination principles of the series and shunt connection, the mathematical model is achieved in a much simpler way. The proposed method is tested on the sample system and compared on various cases. Results: The first swing of rotor angle curve of the faulted system without the resistance is obviously higher than that of with the resistance whereas the second swing of the faulted system, without the resistance, is slightly less than that of with the resistance. The critical clearing time of the system with the resistance is better than that of with resistance. Conclusion: It was found in this study that the resistance of the transmission line should be included for investigating the transient stability of the power system. The resistance of the line provides the better results of the critical clearing time of the system but it provides the negative effect on damping improvement.