Abstract: Due to the lack of unified standards for the hierarchical protection configuration of medium voltage distribution lines, it is urgent to find a quantitative evaluation method to evaluate various hierarchical protection schemes accurately in order to find the optimal allocation scheme. Firstly, the general setting principles of hierarchical protection for distribution lines are introduced based on existing standards and specifications, and the typical configuration scenarios for hierarchical protection are developed according to the maximum action time that can be tuned for outgoing protection of substation. Secondly, taking into account the impact of voltage collapse and main transformer damage caused by delayed tripping of hierarchical protection, the evaluation indexes of the hierarchical protection are defined from four aspects:long-term power outage, short-term power outage, voltage collapse, and main transformer damage, on this basis, the comprehensive evaluation model combining power supply reliability and economy is constructed. Taking a typical medium-voltage distribution line as an example,a comprehensive evaluation of the common hierarchical protection schemes in China is carried out, and the optimal hierarchical protection scheme suitable for the regional grid structure is obtained according to the evaluation results, and the effectiveness of the evaluation method is verified.

    Key words: distribution line; hierarchical protection; voltage collapse; main transformer damage; evaluation index; comprehensive evaluation