汽轮发电机3次谐波电压随负荷变动的理论分析

Theoretical Analysis of the 3rd Harmonic Voltage of Turbo-generator with Load Changes

大型汽轮发电机机端3次谐波电压U3t以及中性点3次谐波电压U3n随有功负荷和无功负荷变动而变化,根本原因是定子绕组3次谐波电压EΦ3受负荷影响,从而影响到3次谐波电压的100%定子接地保护。通过磁导分析法以及傅里叶级数,推导了汽轮发电机转子磁动势和定子电枢反应磁动势产生的EΦ3,通过分析有功和无功负荷变动情况下发电机的磁动势、电势相量,得到了有功和无功对EΦ3的影响关系。分析表明,转子q轴方向上的小齿易饱和是影响EΦ3的重要原因,中性点接地设备参数的非线性可能是导致U3t/U3n发生变化的一个原因。

While active and reactive power change, the 3rd harmonic voltages at the terminals （U3t） and at the neutral （U3n） of large-sized turbo-generator also change. The basic reason is that the load change causes the 3rd harmonic voltage changing of stator windings （Eφ3）, so that the 100% stator ground fault protection based on the 3rd harmonic voltage will be influenced. By magnetic field analysis method and Fourier series, Eφ3, which is generated by field magnetomotive force （MMF） and armature MMF, is studied. By studying the MMF and electromotive force （EMF） phasors while active or reactive power changes, the influence relationship of the active or reactive power change to Eφ3 is obtained. The analysis results indicate that it is an important factor to affect Eφ3, due to the saturation of the rotor teeth at q axis. And it may be a reason of U3t/U3n changing that the parameters of the neutral grounding device are non-linear.