Eccentric bus-bar testing method of the shielding effect of heavy current transformer with shielding coils

To equivalently test the shielding effect of heavy current transformer (HCT) with shielding coils in laboratory, an eccentric bus-bar testing method has been used to simultaneously simulate the effect of the primary bus-bar and adjacent bus-bar since 1970s. But still there hasn´t been an effective way to determine the crucial parameters, especially the eccentric distance, which means the distance from the center of the eccentric bus-bar to the center of HCT. This paper presents several analytical formulas to determine the eccentric distance and relevant parameters in the testing method, which may overcome the present difficulty. The formulas are derived from magnetic circuit model, and further verified by finite element method (FEM). Numerical results show that these formulas are effective and easy to use in the testing of HCT. Further more, if the eccentric current, which should be equal to the original primary current, is still too high to reproduce in laboratory, auxiliary and compensating windings could be adopted to reduce it.