基于励磁电流差异的调相机失磁保护方案

Excitation loss protection scheme based on excitation current difference for synchronous condenser

首先研究了调相机的失磁故障行为及失磁调相机的暂态响应,结果表明已处于失磁状态的调相机在系统电压变化时仍有一定的无功响应能力。在此基础上,分析了基于无功反向特征的已有失磁保护方案在故障检测及保护动作方式上的不足。为了进一步优化调相机的失磁保护,深入研究了调相机的失磁过程并得出了失磁故障后励磁电源输出的测量励磁电流与励磁磁动势对应的实际励磁电流大小存在明显差异的故障特征。然后建立了实际励磁电流的计算模型,解决了实际励磁电流值不能直接测量的问题。在此基础上,构建了基于励磁电流差异特征的失磁保护判据,优化了保护动作方式,提出了相应的调相机失磁保护方案。最后,在PSCAD中建立了包含调相机在内的实际直流输电系统模型,通过仿真对比已有失磁保护方案及所提失磁保护方案的作用,结果验证了所提失磁保护方案的有效性。

Firstly,behavior of SC(Synchronous Condenser)during the excitation loss and the transient response of SC with excitation loss fault are analyzed.The results indicate that the faulty SC still has certain reactive power response to system voltage variation.On this basis,the defects of the existing excitation loss protection scheme based on the reverse reactive power characteristic in the fault detection and the protection operation are analyzed.To further optimize the excitation loss protection of SC,the excitation loss process of SC is deeply analyzed,and the fault characteristic that the measured excitation current produced by the excitation source is obviously different from the actual excitation current corresponding to the actual excitation magnetomotive force is obtained.Then,the calculation model of the actual excitation current is established,which solves the problem that the actual excitation current cannot be measured directly.Then,the excitation loss criterion based on the excitation current difference is proposed,and the corresponding protection scheme with the improvement of the operation mode is presented.Finally,the direct current power transmission model based on the practical project equipped with SC is built in PSCAD,the effectiveness of the proposed excitation loss protection scheme is verified by comparing with the effects of the existing excitation loss protection scheme.