Research on Line Fault Protection Methods for Three-Terminal High Voltage Direct Current Transmission Systems Based on Voltage Source Converter

In recent years, high-voltage direct current (HVDC) transmission systems based on voltage source converters (VSC) have emerged as a prominent and widely discussed solution for integrating large-scale onshore wind farms into the power grid. These systems have gained significant attention due to their ability to efficiently transmit large amounts of renewable energy over long distances with minimal losses. The VSC-HVDC technology offers several advantages, including flexible power control, the ability to connect to weak AC grids, and the capacity to maintain stable operation even under varying power flow conditions. As the demand for renewable energy integration grows, VSC-HVDC systems have become a key focus in the development of modern power grids, providing a reliable and effective means of harnessing and delivering wind energy to meet increasing electricity demands. Protecting against DC faults in multi-terminal VSC-HVDC networks presents significant difficulties. This study examines the behavior of fault currents in a three-terminal VSC-HVDC setup, where currents can surge dramatically within milliseconds during transient events like capacitor discharge and diode freewheeling following a DC fault. A novel approach for detecting and isolating DC line faults from one end in such three-terminal systems is introduced. This method employs an under-voltage criterion to effectively differentiate between fault states and normal operating conditions in the system. By connecting a DC reactor to remain within the operational capacity range of the circuit breaker, thereby preventing damage to the system components. Additionally, the method provides a recommended range of inductance values for the current-limiting reactor, ensuring optimal performance under various fault scenarios. To validate the effectiveness of the proposed protection scheme, the PSCAD/EMTDC simulation software is utilized to simulate. The simulation results demonstrate the accuracy and reliability of the proposed scheme, confirming its ability to correctly identify and respond to faults while maintaining system stability and protecting critical equipment. This approach offers a robust solution for enhancing the protection of multi-terminal VSC-HVDC systems.