A Novel Transient Voltage Pilot Protection Method for Hybrid MTdc Transmission Systems

Traditional high voltage direct current protection methods based on a traveling wave have limited identification capability for near-end, far-end, and high-impedance system faults and cannot meet the reliability requirements for system protection. To address these shortcomings, this article proposes a pilot protection method based on the high-order difference transient voltage. First, the propagation of fault traveling waves is analyzed, and it is studied how the inhibition of high-frequency (HF) components by boundary components causes differences in the HF components between the fault voltages during internal and external faults. Next, the amplitude-frequency characteristics of a high-order difference are analyzed, and it is shown that this difference exhibits excellent high-pass filter capabilities. Namely, by applying the high-order difference to the fault voltage on both sides of the boundary components, the HF differences between the two voltages can be significantly amplified. Then, the start-up element and the fault direction identification elements are constructed, and a complete protection method is developed. Finally, a hybrid multiterminal direct current system is established using a real-time digital simulator, and numerous experiments are conducted to verify the proposed method. The results show that the proposed protection method can rapidly identify both internal and external faults with high reliability. In addition, it is demonstrated that the proposed method exhibits strong high-impedance fault resistance, is insensitive to noise and fault location, and does not have high requirements for time synchronization and communication, making it easy to implement in engineering applications.