城轨交通配电变压器励磁涌流特性及保护配合曲线研究

Excitation Inrush Current Characteristics and Protection Coordination Curves of Distribution Transformer for Urban Rail Transit

城市轨道交通供电系统配电变压器担负车站所有Ⅰ、Ⅱ和Ⅲ级低压负荷的供电,其重要性不言而喻。现阶段城市轨道交通配电变压器的保护主要由中压馈线综合保护装置实现,主要包括速断保护、过流保护以及过负荷保护。由于上述保护均采用定时限,为躲避配电变压器送电引起的励磁涌流,需调大电流和时间整定值,虽然调整后的整定值可以避免保护误动,但牺牲了一定的速动性和灵敏性。本文对配电变压器的励磁涌流特性、过负荷能力、变压器高低压侧短路电流等进行深入分析和研究,同时结合IEC60225标准的反时限曲线进行拟合,给出更贴合配电变压器实际运行的保护配合曲线。

Distribution transformers are utilized to undertake voltage loads of gradeⅠ,Ⅱ,Ⅲ,and they are playing more and more important roles in electrified urban transit systems.The protection of distribution transformers is generally realized by MV feeder circuit breaker with integrated relays,which can provide instantaneous over-current protection,time delayed over-current protection and overload protection in recent years.However,due to the definite time limit curves are applied to the above-mentioned protection relays,the setting values of current and time delay have to be increased intentionally to avoid false trip caused by the excitation inrush current from an energizing distribution transformer.Although the coordinated setting values can protect the transformer,it sacrifices a certain amount of speed of operation and sensitivity.This paper facilitates in-depth the analysis on inrush current characteristics,overload capacity,and short-circuit currents on primary and secondary sides of the transformer,which is in conjunction with IEC 60225 standard inverse time curves,and gives a better fit for actual operation of distribution transformer.