Research on Ground Fault Mechanism and Optimization Strategy of Low-voltage DC System in UHV Converter Station

The low-voltage direct current (DC) system serves as a critical and indispensable component within the infrastructure of a converter station. It is primarily responsible for providing continuous and reliable power to essential subsystems, including relay protection, automated control mechanisms, signaling networks, computer monitoring frameworks, emergency lighting arrays, and alternating current (AC) uninterruptible power supplies. Consequently, the stable and uninterrupted operation of this low-voltage DC system directly dictates the overall safety, reliability, and operational stability of both the high-voltage direct current (HVDC) transmission network and the interconnected AC grid. Despite its importance, these systems are susceptible to ground faults, which can compromise station integrity and lead to cascading failures if not promptly addressed. This paper comprehensively introduces the architectural framework and operational characteristics of the low-voltage DC system within an ultra-high voltage (UHV) converter station, detailing the fundamental calculation principles required for system design and fault analysis. To bridge theoretical concepts with practical applications, this study conducts an in-depth empirical analysis of two distinct DC ground fault cases recently documented at operational converter stations. By systematically dissecting these real-world incidents, the research identifies the underlying mechanisms triggering such faults and evaluates the efficacy of current diagnostic protocols. Furthermore, it summarizes advanced fault-finding methodologies tailored for rapid and accurate DC grounding fault detection. Finally, the paper proposes a series of strategic optimization suggestions aimed at enhancing system resilience, improving fault isolation techniques, and ensuring the long-term operational security of UHV converter stations.