某1000MW机组轴系次同步振荡仿真研究

Simulation of subsynchronous oscillation caused by fault in converter station of a 1000MW unit shafting

因换流站的直流单元发生故障,导致某型超超临界1 000 MW机组发生持续性次同步振荡。为评估该次同步振荡事件对机组轴系安全性的影响,考虑电气和机组轴系的耦合影响,建立了超超临界1 000 MW机组发生次同步振荡的数学模型,并采用数值仿真法,通过在系统电网侧串接1个小幅值的次同步频率电压,激发轴系的次同步振荡,模拟实际次同步振荡在该机组轴系上产生的扭矩。结果表明:该超超临界1 000 MW机组机头转速偏差稳定在0.002 86p.u.(标幺值,下同),机尾转速偏差稳定在0.001 20p.u.,与振型曲线基本吻合(机尾、机头振型比约0.4);主要振荡频率23.8Hz,为轴系的第2阶扭振固有频率;低发对轮间扭矩最大,在机组实际运行中,应密切监测低发对轮的状态和扭转振动。

Due to DC unit fault of converter station, continuous subsynchronous oscillation occurred in an ultra supercritical 1 000 MW unit. In order to evaluate the effect of this subsynchronous oscillation event on security of the unit shafting,mathematical model for this ultra supercritical 1 000 MW unit with subsynchronous oscillation was established,considering the coupling effect between the electric and unit shafting. By using simulation method, a small amplitude sub synchronous frequency voltage was connected in the grid-side of system, and subsynchronous oscillation of the shafting was inspired,to simulate the torque acting on the ultra supercritical 1 000 MW unit shafting during the subsynchronous oscillation. The results show that,the die speed deviation in this ultra supercritical 1 000 MW unit is stable at 0. 002 86 p. u. ,and that of the machine tail is stable at 0. 001 20 p. u. ,which is basically the same as the vibration curve （the vibration ratio of the machine head to the end is about 0.4）. The main oscillation frequency is 23.8 Hz, which is the natural frequency of the second order torsional vibration of the shaft system. The torque between the low generation wheel is the largest, the state and torsional vibration of the wheel should be closely monitored during the actual operation.