Tripping Fault Analysis Caused by Inaccurate Measurement of Optical CT in ±800 kV UHVDC Transmission System

The ultra-high voltage direct current (UHVDC) power transmission systems usually transmit very large amounts of powers, their stability and reliability are of vital importance to the large power grid. This paper analyses a tripping fault caused by the inaccurate measurement of optical current transformer (OCT) in Shaanbei-Wuhan ± 800kV UHVDC transmission system. Combined with theoretical analysis and in-plant testing of the optical CT, a comprehensive understanding of the factors contributing to the fault is achieved. It reveals that optical CT measurement anomalies were significant contributors to the tripping fault. Validation results illustrate the effectiveness in measuring very fast impulse current accurately by adding automatic reset logic in the software programme of OCT. This study provides a guarantee and foundation for the stable operation of UHVDC transmission systems.