高压发电机新型过电压保护

对于并列运行的发电机，当其中一台励磁系统出故障时，有可能导致公共母线的电压升高，如果发电机过电压保护的定值一致，将导致母线上的所有发电机被切除。由于以高压发电机(Powerformer)为电源主体构成的电厂必然存在上述配置，所以需要有妥善方案解决这个问题。该文在研究发电机机端电压和无功功率输出的基础上，指出现有用于并列运行的高压发电机过电压保护方案的不足，并提出了新的过电压保护方案。该保护除检测过电压故障外，还通过发电机无功功率输出的变化量识别引发过电压的根源，有利于获得保护的选择性。此外，采用补偿系数修正保护的动作时间，能最先切除对母线过电压影响最大的发电机。该保护方案的有效性通过PSCAD/EMTDC仿真试验证实，且该保护方案的应用范围并不局限于高压发电机。

A Novel Overvoltage Protection for Powerformer

For the generators operating in parallel, the common busbar may experience the increase of voltage when the excitation system of one generator is failed. All of the generators connected to this busbar will become isolated if their settings of overvoltage protection are identical. An appropriate solution must be proposed for the plant consisting of Powerformers since the Powerformers always operate in parallel. Based on the analysis of the relation between terminal voltage of a generator and the reactive power output, the disadvantage of the existent overvoltage protection scheme for generators working in parallel have been pointed out, and a novel overvoltage protection scheme is proposed. This protection can not only detect overvoltage events, but make it possible to identify which machine is the source of the overvoltage by virtue of the change of reactive power output. As a result, the selectivity of the protection is realized. Using a compensated factor to modify the operating time of the protection, the generator which has the most vital impact on the overvoltage of the busbar will be tripped at first. The effectiveness of this scheme is validated with the PSCAD/EMTDC simulation tests. It should be pointed out that the application of this protection scheme is not restricted to Powerformer.