有功不平衡下计及低频减载影响的输电线路过载热保护

Thermal overload protection of transmission lines considering the influence of UFLS under active power imbalance

由于内外部扰动引起的有功不平衡,系统频率和线路电流会出现明显的波动、过渡及恢复过程,需关注系统状态恢复过程中的导线热力安全,采取合理的保护策略。分析了电网有功不平衡下电流和频率的动态特性,研究了不同低频减载方案对频率恢复速率和导线温升过程的影响,提出了电网有功不平衡下计及低频减载影响的输电线路过载热保护策略。通过IEEE39节点系统仿真测试,验证了所提策略的有效性。仿真结果表明:不同类型的大扰动下,不同的低频减载布点位置和数量以及低频减载整定方案对导线温升响应的影响及延迟过载热保护动作时间的效果不同。所提出的输电线路过载热保护能够最大限度地挖掘线路耐受事故过负荷的能力,在兼顾系统频率恢复的同时,避免线路温升越限出现新的连锁故障。

Power frequency and transmission line current show a distinct process of fluctuation,transition,and recovery when massive active power imbalance occurs,which is caused by internal and external disturbances.Thus,attention should be paid to the thermal safety of conductor,and reasonable protection strategy should be adopted during the recovery of power system.In this paper,the dynamic characteristics of power frequency and line current are analyzed.Furthermore,the influence of different UFLS schemes on the frequency recovery rate and conductor temperature rise response is also studied.Thermal overload protection of transmission lines considering the influence of UFLS under active power imbalance is proposed.The effectiveness of the proposed protection strategy is verified on IEEE 39-bus power system.The simulation results show that different location,number and setting scheme of UFLS have different influence on conductor temperature rise response and time delay of protection under different disturbances.The proposed overload thermal protection can maximize the capacity of the transmission lines to withstand emergency overload,and avoid new cascading fault due to conductor temperature off-limit when the power frequency is recovery.