次同步扭振互作用机制解析

Insight Into Mechanism of Subsynchronous Torsional Interaction

文中分别推导了次同步频率阻性电流和次同步频率感性电流产生的2个电磁转矩偏差分量表达式,发现次同步频率阻性电流产生负阻尼转矩,而次同步频率感性电流产生同步转矩。在此基础上,揭示次同步频率的等值电阻与电抗比过大是导致机组轴系扭振模态弱阻尼或负阻尼的根本原因。同时,阐释了由于机组轴系机械弹性系数远大于电气系统引起的上述阻尼转矩系数和同步转矩系数,次同步扭振互作用只发生周期失稳。最后,以改编的IEEE第一标准模型为算例,应用时域仿真和特征值法验证上述分析的正确性。

This paper deduces formulas for two components of electromagnetic torque respectively caused by subsynchronous frequency resistive and inductive currents. It is observed that subsynchronous frequency resistive current provides negative damping torque, while its inductive current provides synchronous torque. Larger ratio of subsynchronous frequency equivalent resistance to reactance results in oscillation of weak or negative damping of torsional modes of turbine-generator shafts. Only periodic instability can occur in terms of subsynchronous torsional interaction because shaft mechanical elasticity coefficients are far larger than damping torque and synchronous torque coefficients caused by electrical system. Finally, modified first IEEE benchmark model is adopted to justify the analyses with time domain simulation and eigenvalue method.