Analysis of Transformer Differential Protection Malfunction Occurred in Intelligent Substation under VFTO Functionaper

The transformers’ differential protection of 110 kV intelligent substation misacted. With the fault recording document of the Oscilloscope and various data of field, the reason of the accidence was carried out. the electromagnetic interference (EMI) problem of switching operation overvoltage, especially very fast transient overvoltage (VFTO), on electronic transformers in substations can cause the serious problem which is the reason of the accidence. Transformers’ differential protect set point is reached for the false secondary current of electronic transformers. This paper analyzes the transmission characteristics and influencing factors of VFTO in 110kv GIS substation, and puts forward the field scheme of improving the anti VFTO interference of electronic transformer. After on-site modification, impaction of VFTO has significantly reduced on the output current of electronic transformer, which effectively preventing the recurrence of such accidents.