输电线路动态安全裕度辨识及自适应过负荷保护

The existing overload protection of transmission line takes current or impedance exceeding the normal boundary as its action criteria. This action strategy cannot adapt to the surge overload during power flow transferring, and even has accelerated the cascading trip of power system in several block out events. The drawback of the existing overload protection is that its action strategy does not react the electric-thermal coupling mechanism of “current step change, conductor temperature increase, sag growth, security margin reduction” when transmission line sustains the overload current. Therefore, this project researches and establishes an adaptive overload protection of transmission line based on transmission line dynamic security margin. This project solves the key scientific issues of dynamic models of thermal deformation response to surge overload under power flow transferring conditions and dynamic evolution rule of transmission line security margin as well as optimization of overload protection. The radial distribution model of conductor temperature considering forced convection condition and temperature rise response calculation of transmission line will be established through parameter identification of thermal circuit model. The sag calculation method considering the features of radial distribution of conductor temperature and the difference of thermal strain parameters between steel core and aluminum strands will be built based on the modified strain accumulation method. Through constructing associated security check criteria of current, conductor temperature and sag, and obtaining the dynamic curves of “overload current—conductor temperature/sag—tolerance time” of transmission line, the starting criteria and action time of overload protection will be adjusted adaptively, which will provide emergency security control of power system with sufficient time, to block up the spread of cascading trip, and reduce the risk of power system blackouts.

现有的输电线路过负荷保护以电流或阻抗超出设定边界作为启动跳闸条件，其动作原理无法适应潮流转移冲击过负荷影响，在多次大停电事故中助推了连锁跳闸发展过程，其缺陷在于未能反应线路承受过负荷时“电流增大→温度升高→弧垂增长→安全裕度降低”的电热力耦合作用传递规律，为此本项目拟研究构建基于线路动态安全裕度的自适应过负荷保护方法。项目拟解决潮流转移过负荷冲击作用下线路的热力变形响应动力学模型和线路安全域动态演变规律及过负荷保护优化关键科学问题，通过热网络参数辨识法建立计及强迫对流条件的导线温度分布模型及温升响应计算方法，通过改进应变累积法建立计及导线温度径向分布特征和钢芯铝股热应变差异的弧垂计算方法，通过构建电流、温度和弧垂关联安全判据以及“过负荷电流—温度/弧垂—耐受时间”动态特性，实现过负荷保护启动条件和动作时间的自适应调整，为电网紧急安全控制赢得更多时间，有效阻断连锁故障发展，降低大停电风险。

电力系统时刻处在各种内外部扰动影响之下，由于扰动而突然产生大的有功不平衡后，系统将会处于振荡、潮流转移过负荷等非故障异常运行工况，由此带来的输电线路事故过负荷问题日益突出。现有过负荷保护的不合理动作助推大范围连锁跳闸事件发展，威胁电网的安全稳定运行。本项目针对事故过负荷情况下输电线路电热安全动态演变规律、过负荷保护和潮流优化控制等关键问题进行了深入的研究。构建了基于热网络模型的输电线路电热特性及温度计算方法，揭示了外部强迫对流与内部电流耦合作用下输电线路的传热机理，能够有效反映潮流转移下导线的径向周向温度分布特性。提出了高温天气下输电线路热力安全校核与预警方法，有助于运行人员动态校核输电线路安全状态，指导输电走廊植被管理和高温天气下线路潮流控制。提出了基于设备过载耐受能力配合的输电通道安全运行策略，能够充分利用设备的短时过载耐受能力，在兼顾设备安全保护的同时为系统安全运行提供传输容量支撑。提出了电网功率振荡期间的输电线路自适应过载热保护，能够在保障输电线路安全的前提下，有效防止系统振荡恢复过程中出现新的连锁故障。提出了计及输电线路电热特性的交直流混联电网过载控制策略，实现较短时间内的安全经济过载控制，有效阻断混联电网连锁跳闸事故发生。