低频功率振荡中距离Ⅲ段动作特性

Operation Condition for Zone 3 Impedance Relays During Low Frequency Power Swings

电网事故过程中的低频功率振荡可以引起输电线路距离保护的不合理动作,扩大停电事故范围。提出距离Ⅲ段保护动作的临界振荡角度和临界振荡频率的直接算法。根据线路两端等值电源电压,建立多项式形式的保护动作条件,直接求解临界振荡角度,在此基础上,分析继电器参数设置、等值电源阻抗和线路充电电容对保护动作条件的影响。假设振荡频率恒定,根据临界振荡角度计算振荡轨迹在保护范围内的停留时间,从而得到不同保护整定时间下引起距离Ⅲ段保护动作的临界振荡频率。仿真分析验证了所提出的算法的可行性和有效性。

Low frequency oscillations following power system contingencies may cause undesirable operation of relay protections on transmission lines and enlarge the blackouts.A direct algorithm for the critical swing angle and frequency to zone 3 impedance relays is presented.The relay operation condition based on critical swing angles is quantified by the equivalent source voltages.The impacts of relay settings,source voltages and line charging on the relay performance are analyzed.With the approximately constant swing frequency,the resident time inside the protection region is found by the critical swing angles to quantify the critical swing frequency under different time settings.The feasibility and effectiveness of the algorithm are validated by the numerical results.