Abstract
Protection of direct current (DC) transmission lines is one of the key difficulties to be urgently solved in the construction of the future voltage-sourced converter (VSC)-based DC grids. In this paper, a novel ultra-high-speed traveling-wave (TW) protection principle for DC transmission lines is proposed which is based on characteristics of modulus voltage TWs. First, the absolute value of the change in amplitude of the 1-mode voltage TW is used to construct the protection starting-up element. Then, the dyadic wavelet transform is utilized to extract the wavelet-transform modulus maxima (WTMM) of 1-mode and 0-mode initial reverse voltage TWs separately, which are used for fault section identification and selection of fault line successively. A four-terminal annular VSC-based DC grid electromagnetic transient model is established in PSCAD/EMTDC, and performance of the proposed novel ultra-high-speed TW protection principle is evaluated. Extensive simulation results under different fault conditions show that the proposed ultra-high-speed TW protection principle is excellent in rapidity, reliability and robustness. Therefore, the proposed novel ultra-high-speed TW protection principle in this paper can be adopted as an outstanding main protection for VSC-based DC grids.
Highlights
The voltage-sourced converter (VSC)-based direct current (DC) grid is a feasible solution to realize wide-area complementarity and flexible consumption of large-scale renewable clean energy, and as a result has bright future and important application value [1], [2]
SIMULATIONS To evaluate the performance of the proposed novel ultra-highspeed traveling-wave protection scheme, an electromagnetic transient simulation model on basis of the actual parameters of Zhangbei ±500 kV VSC-based DC grid shown in Fig. 1 was built, where the sampling frequency for signals is 500 kHz, and the frequency-dependent transmission line is adopted
In this paper, a novel ultra-high-speed traveling-wave protection principle for VSC-based DC grids is proposed, which is based on characteristics of modulus voltage travelling waves (TWs)
Summary
The voltage-sourced converter (VSC)-based direct current (DC) grid is a feasible solution to realize wide-area complementarity and flexible consumption of large-scale renewable clean energy, and as a result has bright future and important application value [1], [2]. X. Pei et al.: Novel Ultra-High-Speed Traveling-Wave Protection Principle for VSC-based DC Grids impedance path for the high-frequency component, with the obvious difference in the ratio of the transient voltages at both sides of the inductor during DC line fault and external fault, fault identification is realized. Based on analysis of features of fault-induced travelling waves (TWs) after DC line fault, two ultra-high-speed TW protection principles for transmission lines of VSC-HVDC systems are proposed in [14], [15]. To solve the integration and transmission of large-scale renewable clean energy resources in this area, a four-terminal annular bipolar VSC-based DC gird demonstration project of which the rated voltage is ±500 kV will be constructed around the end of 2019. Zc is the line characteristic impedance and γ is the corresponding TW propagation coefficient respectively, which can be shown as in frequencydomain form: r0 + jωl0 g0 + jωc0
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