Difficulties in producing CT caused by the current ratio regulation in IEC standard and suggestions of modification

Abstract

Abstract The integer current ratio requirements by standard IEC 61869-2 and users result in the numbers of current transformer (CT) winding turns being decimal, such as 5.94, 9.9, and 14.85. This makes the manufacturing of CTs complex, causing socioeconomic waste. It is pointed out in this paper that if the integer current ratio requirements can be changed to decimals, the number of CT winding turns may be made an integer, which makes it easy to produce low-error CTs. The error refers to the difference between the actual current ratio and the required current ratio for CTs. Additionally, if this change is made, iron core materials do not need to have high permeability. Furthermore, it is better to allow the manufacturers to mark freely the current ratio within a certain range on CT rating plates. The measure of changing the current ratio requirements or changing the way of marking the ratio on rating plates can significantly reduce the manufacturing difficulties and costs of CTs.