Desearch On Fransformer Differential Protection Against CT Saturation

Power transformer, one of the most important elements, is widely used in electric power transmission and distribution. To prevent transformer from damage, current differential protection principle is applied to transformer main protection. The principle and algorithm of transformer main protection has been more and more perfect, but the differential protection mal operation cases still occur due to CT saturation and other reasons. Therefore how to eliminate the influence of CT saturation on transformer differential protection becomes an important research topic of transformer differential protection.The main research is focused on the key problem of anti-CT saturation. This dissertation describes in detail the implementation of differential protection principle and the differential protection in the microcomputer device in transformer differential protection. The author analyse the existing main problems in transformer differential protection, particularly unbalanced current under normal or abnormal condition. Based on the analysis of CT saturation mechanics, the thesis sum up the characteristics of the waveform of the second current and magnetizing current when CT transient saturation, and provides a theoretical basis for the subsequent CT anti saturation scheme.According to the characteristic of current waveform when CT saturation, a scheme of Anti CT saturation is presented for transformer differential protection, which is simulated through a integrated system. Experimental results show that:it can prevent incorrect operation of transformer differential protection when CT saturation; on the other hand it can act correctly when fault occurs in protected areas. In conclusion, the scheme proposed by the author can distinctly enhanc the ability of anti CT saturation of transformer protection device, and achieve the expected design goals.