A Frequency-Based Fault Location Method for Overhead Metallic Return Conductors in HVDC Transmission System

This paper presents an innovative fault location method specifically developed for metallic return conductors of HVDC overhead lines. The proposed approach addresses the inherent limitations of conventional protection schemes when applied to non-energized conductors, introducing a non-traditional technique based on controlled signal injection and frequencydomain sensitivity analysis.

The method consists of injecting a train of impulse signals into the metallic return conductor at regular time intervals. Each impulse is characterized by a specific carrier frequency, derived from a preliminary frequency-domain analysis of the system voltage response. This analysis allows the identification of frequency components that exhibit a strong dependence on the fault location along the line. The injected carrier signals are amplitude-modulated and subsequently processed using dedicated band-pass filters, each tuned to a specific carrier frequency. For a given fault condition, the interaction between the injected signals and the line produces characteristic variations in the amplitude of the filtered components. These variations have been shown to be strongly correlated with the distance between the fault location and the converter station. Certain carrier frequencies exhibit resonance phenomena that become more pronounced as the fault location changes, enabling effective fault discrimination and localization along the metallic return conductor. The proposed fault location system has been fully implemented and validated through time-domain simulations performed using EMT simulation. Detailed models of the metallic return overhead line, signal generators, and frequency-selective filters were developed to evaluate the method performance under various fault scenarios.

The presented methodology introduces a novel protection concept for metallic return conductors in HVDC systems and provides a solid foundation for the development of dedicated fault detection and location schemes.