励磁绕组短路故障下汽轮发电机的电磁稳态特征

Steady-state Electromagnetic Characteristics of Turbine Generator After Field Winding Short-circuit Fault

为了评估励磁绕组匝间短路对汽轮发电机稳态变量的影响,采用有限元方法(FEM)计算了QFSN220-2型汽轮发电机励磁绕组短路故障后的电磁转矩变化,研究了在励磁快速补偿和恒励磁条件下为保持电磁转矩不变发电机的电磁稳态调节方法,研究结果表明:铁磁材料的饱和特性缓和了励磁绕组短路故障发生时的转矩波动,降低了发电机严重短路故障的失稳风险。得到了发电机无功和励磁电流在极端条件下的变化边界,分析了短路位置、程度对故障严重性的影响。发电机过励状态下发生匝间短路故障励磁电流增加较欠励时明显,过励程度越深则励磁电流增加越显著,研究结果为励磁绕组短路故障诊断提供了有益建议。

In order to assess the impact of turn-to-turn short circuit in field windings on steady-state variables of turbogenerator, using the finite element method（FEM）, we calculated the electromagnetic torque of a QFSN-220-2 turbine generator with short-circuit fault in its field windings, and developed an adjustment method that could maintain electromagnetic torque constant under rapid exciting compensation condition and constant excitation condition. We also obtained the limit of changes in generator excitation current and reactive power under extreme conditions, and hence evaluated the impacts of short-circuit location and short-circuit degree on failure severity. Results show that the saturation characteristics of ferromagnetic material not only reduce torque ripple when field windings short-circuit fault occurs, but also decrease the instability risk of generator under serious short-circuit fault. When short-circuit fault of a generator which works under an over-excitation condition happens, its excitation current increases more significantly than that under under-excitation condition; the higher the over-excitation grade is, the more the excitation current increases. The results are useful for the diagnosis of short-circuit faults in rotor windings.