Ultra-high-speed transient-based directional relay for AC transmission lines connected to LCC-HVDC inverter station.

• A practical ultra-high-speed transient based directional protection scheme for AC transmission lines connected to LCC-HVDC inverter station is proposed. • Ultra-high-speed. This paper only uses the 1 ms long data window, and the efficient and convenient SST is used for signal processing, so that the protection algorithm can be completed within 5 ms. • High reliability. This paper uses reliable transient energy as the protection criterion, and the efficient SST to achieve the protection algorithm, which solves the unreliable problem caused by mode aliasing and noise interference, etc. • Immune to commutation failure (CF). The proposed ultra-high-speed protection method can operate within 5 ms, avoiding the influence of CF, and all the simulations prove the reliability of the protection algorithm when CF is unavoidable. Commutation failure (CF) is a common phenomenon existing in the LCC-HVDC system, which threatens the normal operation of AC line protection near the inverter side. To solve this problem, this paper proposes an ultra-high-speed transient based directional protection method based on synchrosqueezing S transform (SST). Firstly, the frequency characteristics of the AC bus near the inverter side and the effect of CF on the action of the relay protection are analyzed in detail. Then, this paper analyzes the propagation mechanism of fault transient components by grid method, and proposes a protection criterion based on the transient energy ratio of forward and reverse current traveling wave fault components, which makes the protection scheme with higher reliability. To adapt to the wildly existed high frequency-low amplitude transient signals, this paper utilizes the novel SST for signal processing. SST takes advantage of S transform and synchrosqueezing wavelet transform, and it is more efficient and convenient. Based on the project parameters of the Yun-Guang LCC-HVDC system, a PSCAD simulation model is established. Extensive simulation tests and comparison with other algorithms verify the superiority of the proposed protection method under various fault conditions, as well as its immunity to CF. [ABSTRACT FROM AUTHOR]