基于振荡边界圆的失磁保护新判据研究

Research on a novel loss of excitation protection criterion based on impedance circle of oscillatory boundary

提出了一种新的失磁保护判据——振荡边界圆判据,来解决传统的失磁保护阻抗元件无法区分失磁与振荡这一问题。推导了发生振荡时机端阻抗轨迹的方程,经过分析得到系统发生低励磁振荡时,低励程度越深,机端阻抗轨迹圆越小,并且形成包含关系。根据这一结论,提出振荡边界圆判据,当机端测量阻抗轨迹进入振荡边界圆内,认为发生了失磁故障,保护直接动作,通过仿真验证了该判据的正确性。针对振荡边界圆判据,提出了一套新的失磁保护方案,并通过实例分析,验证了新失磁保护方案的有效性。

This paper proposes a new loss-of-excitation（LOE） protection criterion, namely the impedance circle of oscillation boundary criterion, to solve the problem that traditional LOE protection impedance unit cannot distinguish LOE from oscillation. Firstly, the equation of impedance trajectory at generator terminal is established, and based on the equation, through the analysis, the conclusion can be drawn that when low excitation oscillation occurs, the deeper the extent of low excitation is, the smaller the impedance circle at generator terminal becomes, and the smaller circle is included in the bigger one. Then according to that conclusion, the impedance circle of oscillation boundary criterion is proposed. When the impedance trajectory measured at generator terminal enters into the impedance circle of oscillation boundary, loss-of-excitation is thought to occur and the protection devices act directly. Based on the impedance circle of oscillation boundary criterion, a new loss-of-excitation protection scheme is proposed and the effectiveness of the scheme is verified by the specific test case.