汽轮发电机中静止励磁轴电压的分析与抑制

Analysis and suppression of shaft voltage in turbonator with static excitation system

采用静止励磁的大型汽轮发电机,整流输出的共模电压施加在轴系对地电容上,产生一种交流轴电压。该轴电压大于20V时,容易击穿油膜,产生电腐蚀,严重损伤轴承。为了抑制这种轴电压,提出了一种对称互补RC模块的方法。该模块由转子汽机端、励磁端无源RC接地电路与整流输出侧的对称滤波器构成。汽机端RC接地电路主要消除直流和低频轴电压;励磁端RC电路主要抑制高频轴电压脉冲。当接地电刷故障时,对称滤波器起后备保护作用,综合运用可以将各种轴电压降低到无害水平。通过对一台600MW汽轮发电机励磁系统和轴系建模仿真,将采取不同防范措施后的仿真结果进行对比分析,验证了该方法的有效性和可靠性。

The static excitation system （SES） of large turbonator has resulted in a type of AC shaft voltage （SV） when the common-mode voltage （CMV） resulting from rectifiers adds on the capacitance to ground of the shaft line. The shaft voltage above 20 V is easy to break the oil films, causing electro-erosion and serious damage in the bearings. A new symmetrical and complementary RC module has been proposed to suppress the voltage. The module includes the RC-circuits to ground both on the exciter and turbine end, the symmetrical filter on the DC side of rectifier. The RC-circuit on the turbine end is mainly used to eliminate the DC and low frequency shaft voltage; while the one on the exciter end can suppress the high frequency shaft voltage peaks. When the grounding brushes are ineffective, the symmetrical filter will act as the backup protection, which will suppress all kinds of shaft voltages to harmless levels. A module of SES and shaft line of a 600 MW turbonator is built for simulation. Compared with the simulation results of different countermeasures, the method is proved to be valid and reliable.