超高压变压器断相保护研究

2021年12月26日，某750 kV变电站变压器C相高压侧套管内部载流连接件发生断裂，套管上节发生位移，由于在低负荷工况下现有变压器保护对断相故障无法判别，导致现场变压器长时间断相运行，套管会有随时掉落的风险，可能造成变压器内部爆燃、绝缘击穿、绕组变形等永久性损伤。为应对轻载工况的断相故障对变压器安全运行的威胁，提出基于测量级电流互感器的变压器断相保护方案，通过检测变压器高压侧电流、电压及低压侧套管电流，有效鉴别出变压器轻载工况下的断相故障，解决变压器保护对断相故障检测不灵敏、隔离不及时的问题，保障电网安全稳定运行。

Research on open-phase protection of EHV transformer

On December 26,2021,the upper section of the bushing at the high voltage side of phase C of main transformer in 750 kV substation was displaced and fractured resulting in the phase C open-phase of the transformer.Under low load conditions,there was no protection alarm for a long time.If the open-phase occurs in the bushing of the main transformer,there was a risk that the bushing would fall and may cause permanent damage such as internal deflagration,insulation breakdown,winding deformation of the main transformer.In order to deal with the threat of open-phase failure,an open-phase protection scheme of the transformer based on the measurement level current transformer was proposed.By detecting the current and voltage at the high voltage side of the transformer and the bushing current at the low voltage side of the transformer,which can effectively identify the open-phase failure of the transformer under the light load condition,and the problems were solved that the transformer protection was not sensitive to the open-phase detection and the tripping was not timely,It is conducive to the safe and stable operation of the power grid.