什么是发电机的直轴瞬变电抗Xd’与发电机结构有什么关系 What is the direct axis transient reactance Xd 'of a generator and what is its relationship with the generator structure

Xd’是代表发电机运行中三相突然短路，初始时间(阻尼绕组的电流衰减后)的过渡电抗。直轴瞬变电抗是发电机额定转速运行时，定子绕组直轴总磁链产生的电压中的交流基波分量，在突变时的初始值与同时变化的直轴交流基波电流之比。它也是发电机和整个电力系统的重要参数，对发电机的动态稳定极限及突然加负荷时的瞬态电压变化率有很大影响。Xd’越小,动态稳定极限越大，瞬态电压变化率越小；但Xd’越小，定子铁芯要增大，从而使发电机组体积增大，成本增加。Xd’的值主要由定子绕组和励磁绕组的漏抗值决定。

结构上xd'与电负荷A极距T有如下关系:

k为比例系数。可见要降低xd’必须减小A或加大T，都将使发电机尺寸增大。

Xd 'represents the transient reactance at the initial time (after the damping winding current decays) of a sudden three-phase short circuit during generator operation. The direct axis transient reactance is the ratio of the AC fundamental component in the voltage generated by the stator winding's direct axis total magnetic flux at the rated speed of the generator, to the initial value at the time of the sudden change and the DC fundamental current that changes simultaneously. It is also an important parameter of the generator and the entire power system, which has a significant impact on the dynamic stability limit of the generator and the transient voltage change rate when suddenly loaded. The smaller the Xd ', the greater the dynamic stability limit and the smaller the transient voltage change rate; But the smaller the Xd ', the larger the stator core, resulting in an increase in the volume and cost of the generator. The value of Xd 'is mainly determined by the leakage reactance values of the stator winding and excitation winding.

Structurally, xd 'has the following relationship with the pole distance T of electrical load A:

K is the proportionality coefficient. It can be seen that reducing xd 'requires reducing A or increasing T, both of which will increase the size of the generator.