发电机高压侧电压控制在抑制云广直流孤岛过电压中的作用

Effect of Generator High-voltage-side Voltage Control on Mitigating Overvoltage in Islanded Yunnan-Guangdong UHVDC Sending System

云广直流送端孤岛运行方式下发生直流闭锁时,系统将产生很高的工频过电压,是孤岛运行控制的关键问题。扰动后电压动态过程可分为不同阶段,文中分析了不同阶段影响过电压水平的主要因素。扰动后数百毫秒后的第2阶段电压虽然低于第1阶段,但持续时间较长,电压控制的要求更高,而且受发电机励磁控制的影响显著。短路比和过电压水平密切相关,提出了分阶段短路比的概念。发电机高压侧电压控制通过减小发电机侧恒定电压源和系统之间的电气距离,增大扰动后第2阶段的短路比,抑制过电压,并保证正常运行时合理的电压水平和无功分配。仿真结果验证了高压侧电压控制抑制过电压的效果。

High amplitude overvoltage will occur in the AC system after the DC block in the islanded operation mode of YunnanGuangdong ultra-high voltage direct current(UHVDC)sending system.This is a key problem of islanded operation.The dynamic process of voltage can be divided into several phases.This paper analyzes the major factors influencing the overvoltage level in different phases.The overvoltage in hundreds of milliseconds after disturbance in phase two is lower than that of phase one,but the duration is longer and the criterion of voltage is higher.The voltage level of this phase is notably affected by excitation control of generators.The short-circuit ratio is closely related to the overvoltage level and the short-circuit ratio differs from phase to phase.The voltage control of the generator high-voltage-side increases the short-circuit ratio of phase two after disturbance and mitigates the overvoltage by reducing the electrical distance between the constant voltage source and the system.The rational voltage level and reactive power distribution in normal operation is guaranteed.The effectiveness of the high-voltage-side voltage control is verified by simulation results.