The early detection of short-circuit fault in the active low-voltage AC system

The distributed power supply decentralized access to the low-voltage side of the distribution network transforms the existing low-voltage AC system into an active low-voltage AC system. The original low-voltage AC short-circuit detection methods are no longer applicable. In this paper, a short-circuit early detection method suit-able for different branch types in the active low-voltage AC system is proposed. Based on the analysis of the transient characteristics of the active low-voltage AC short-circuit, a short-circuit time-varying vector theory and a fast method for solving its modulus length are proposed. Then, we construct a branch state variable containing time-varying vector modulus length difference information of current and voltage. The constructed branch state variable can reflect the characteristics of short-circuit state in real-time, which greatly improving the reliability of fast short-circuit detection. Finally, the early detection of short-circuit fault can be realized by comparing the branch state variable with the set detection threshold. The physical experiment system experiments show that the proposed short-circuit early detection method is effective and reliable. Compared with the existing short-circuit fast detection method, the detection time is reduced by 3-5 ms. Moreover, the short-circuit breaking and current limiting can be achieved by combining with the fast protection mechanism, and the current limiting ratio is as low as 0.33.