Power system of State Grid continuously happened several of 220-500 kV instrument transformer damage accidents

and caused serious influence to safe operation of power grids. In response to these accident

State Grid launched secondary load investigation of instrument transformer

involving 18 220 kV to 500 kV substation of nine power companies of provinces and municipalities. Through field measurement

statistical analysis showed that the vast majority secondary practical burden of instrument transformer lower than 25% rated burden

and does not meet the relevant technical regulations. This paper discussed secondary rated capacity designed a oversize value

it seriously affected the transformer metering

measurement

protection performance and lead to increase of transformer size

weight and cost

does not meet the requirements of environmental protection and green power

but also resulted in deterioration of transformer integrated features

including electrical and mechanical performance. Finally

this paper put forward design principle to reduce the secondary load and reduce secondary windings

and suggested that the relevant standards and norms of instrument transformer should carrying out revision and research.