一种换流变压器零序过流保护改进方案

An Improved Scheme for Zero-sequence Over-current Protection of Converter Transformers

针对某换流站换流变压器空充时零序过流保护误动这一事故,根据故障录波器波形证实了此次保护为正确动作。通过对比发现:国家电力调度继电保护处和南方电网电力调度继电保护处,在整定换流变零序过流保护时基于的整定原则不一致。经优化零序过流保护逻辑,将空充标志状态引入零序过流保护,使得保护装置能够在判别出换流变处于空充时自动投入零序过流保护的二次谐波闭锁功能,正常运行时退出保护的二次谐波闭锁功能。既能确保空充时零序过流保护不误动,又能保证正常情况下发生接地故障时零序过流保护的可靠性。最后通过将故障录波器波形进行故障回放验证了方案的正确性。

With respect to a maloperation of zero-sequence over-current protection of the converter transformer at a converter station during transformer charging, the waveform from the fault oscillograph verifies that it is a correct protection action. Through comparison, it is found that the power dispatch relay protection ＆.partment of the State Power Grid and that of the China Southern Power Grid apply different principles for setting zero-sequence ow＇r-current protection for the converter transformer. Though optimization of the zero- sequence over-current protection logic1 zero-sequence over-current protection is applied to the charging mark state1 so that the protection device can automatically initiate second harmonic lock for zero-sequence over-current protection when it figures out the converter transformer is in charging state. During normal operation ~ the lock function is not in effect. In this way, no maloperation of zero-sequence over-current protection will occur during charging. Furthermore, the reliability of zero-sequence over-current protection is ensured in case of a grounding fault under normal conditions. Finally, fault playback through the fault oscillograph verifies the correctness of this scheme.