Eccentric Bus-Bar Testing Method of the Shielding Effect of a Heavy Current Transformer With Shielding Coils

To equivalently and effectively test the shielding effect of a heavy current transformer (HCT) with shielding coils in a laboratory, an eccentric bus-bar testing method has been used to simultaneously simulate the effect of primary bus bar and adjacent bus bar since 1970s. However, there has not yet been an effective way to determine the crucial parameters, particularly the eccentric distance, which means the distance from the center of an eccentric bus bar to the center of an HCT. This paper presents several analytical formulas to determine the eccentric distance and relevant parameters in the testing method, which may overcome the difficulty at present. The formulas are derived out from a magnetic circuit model and further verified by a finite-element method. Numerical results show that these formulas are effective and easy to use in the testing of an HCT. Most importantly, the source of an equivalent relative error has been also investigated in detail. Furthermore, if the eccentric current, which should be equal to the original primary current, is still too high to be reproduced in a laboratory, auxiliary and compensating windings could be adopted to reduce it.