大型汽轮发电机新型中性点引出方式的研究

汽轮发电机绝大多数中性点侧引出3个端子,通常只装设完全纵差保护,因而不能保护绕组匝间短路;中性点侧引出4个或6个端子并装设分支电流互感器,能够大大提高主保护方案的性能,却又带来电机设计制造的难度.为了解决上述矛盾,给大型汽轮发电机提供功能全面的主保护,提出了一种新型的中性点引出方式及主保护方案.提出将A,B相的第2分支单独引出并装设分支电流互感器,再将A1,B1,C1和C2分支接在一起形成中性点侧第3个引出端子并装设电流互感器;然后以2台300 MW汽轮发电机为例,在全面的内部故障仿真计算的基础上对新型主保护方案的灵敏度进行了校核,发现其性能显著优于传统的发电机中性点引出方式及保护方案的配置,并且该方案相比于中性点侧引出4个或6个端子的方案,对发电机的结构改动要求相对较低,更易于在工程上实现.

Study on New Leading-out Mode of Neutral Points of Large Turbo-generator

To provide overall protection to large turbo-generators, a new approach about leading-out mode of neutral points and disposition of protection schemes is presented. There are three terminals at the neutral point in most large generators. Complete longitudinal differential protection is the most commonly used method for stator winding protection, although it can not detect turn-to-turn faults in a same phase since there is no difference in the current entering and leaving the phase winding, To improve protection performance, it is necessary to lead out four or six terminals at the neutral point of large turbo- generators. However this can cause great changes of electrical machine design and manufacture. To solve this problem, the paper suggests that the second branch of phase A and that of phase B are led out and equipped with current transformer in the new leading-out mode. In addition, the first branches of three-phase and the second branch of phase C are connected to form the third leading-out terminal. By doing so, the incomplete longitudinal differential protection of phase C is different from that of phase A and phase B. To examine the sensitivity of the new protection scheme, two turbo-generators of 300 MW are simulated using the proposed multi-loop method. Simulation results indicate that the performance of the new protection scheme is much better than that of the traditional protection.