Inverse time overcurrent protection for low-frequency wind farm transmission lines based on transient current components

• Transient Current Energy. • Transition Resistance Compensation Coefficient. • Two stage inverse time protection. • A novel quick action protection scheme. • Durable transition resistance, optimizing and accelerating traditional inverse time protection. Low-Frequency Transmission Systems (LFTS) integrate the benefits of both high-voltage alternating current (HVAC) and high-voltage direct current (HVDC) transmission technologies. This combination makes LFTS a significant innovation for transmitting large amounts of power over extended distances. When faults occur on offshore wind farm transmission lines operating at low frequencies, the fault characteristics exhibited by electronic-based power sources at both ends are distinct from those of conventional power sources. Consequently, the magnitude of short-circuit currents at both line ends is restricted, which affects the effectiveness of traditional inverse-time overcurrent protection mechanisms. Drawing inspiration from conventional inverse-time overcurrent protection and concentrating on fault components, this study introduces a two-stage inverse-time protection method based on the structural and fault characteristics of low-frequency systems. This approach utilizes the integral of the fault component current magnitude to construct the transient current accumulation, which serves as a variable in the inverse time equation. This technique minimizes the effect of current fluctuations on the protection operation time. Additionally, this study incorporates a transition resistance compensation coefficient to ensure swift protection activation during high-resistance faults. The proposed scheme utilizes single-ended data within a short time window and does not require a high sampling frequency, thus making it highly suitable for practical engineering applications. A low-frequency system model was established using the Real-Time Digital Simulator (RTDS) platform. Extensive simulation results demonstrate that the proposed scheme exhibits reliable operating characteristics under various fault types and possesses robust tolerance to high transition resistance.