The master's thesis addresses the performance and reliability of distance protection of transmission lines under dynamic conditions in a power system, with a particular focus on power swing blocking (PSB). The study analyzes the issue of unwanted tripping of distance relays during stable power swings and the need for reliable tripping in the case of loss of synchronism. The objective of the thesis is to develop an open-source simulation model that demonstrates the occurrence of power swings on high voltage transmission lines following the initiation and clearing of a fault in the medium voltage network.
To achieve the stated objectives, a simplified Single Machine Infinite Bus (SMIB) model was employed, representing a synchronous generator connected to an infinite bus. This reference model is widely used in research, as it provides a straightforward framework for studying fundamental aspects of system stability and power swings. The work first presents the principles of distance protection, including power swing blocking (PSB) and out-of-step tripping (OST), and then develops a simulation model in OpenModelica using the open source OpenIPSL library, incorporating all key system components. To validate the reliability of the open source approach, a reference model was also implemented in MATLAB/Simulink, enabling a direct comparison of system responses.
Several simulations were carried out to demonstrate that power swings occur in the system after fault clearing. By analyzing the trajectory of the impedance locus, scenarios were identified where distance protection, without additional functions, could result in undesired tripping. The results confirm that open-source tools can be reliably used to model and study advanced protection functions in power systems. The proposed approach offers transparency, flexibility, and accessibility, making it valuable for both research and educational purposes. The applied methodology successfully bridges the field of power system stability with relay protection algorithms in an open simulation environment, while the results provide useful insights into the operation of distance protection during power swings and can support further improvements in the security and reliability of the power system.
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