Modelling and Optimization of Four-Segment Shielding Coils of Current Transformers

Abstract

Applying shielding coils is a practical way to protect current transformers (CTs) for large-capacity generators from the intensive magnetic interference produced by adjacent bus-bars. The aim of this study is to build a simple analytical model for the shielding coils, from which the optimization of the shielding coils can be calculated effectively. Based on an existing stray flux model, a new analytical model for the leakage flux of partial coils is presented, and finite element method-based simulations are carried out to develop empirical equations for the core-pickup factors of the models. Using the flux models, a model of the common four-segment shielding coils is derived. Furthermore, a theoretical analysis is carried out on the optimal performance of the four-segment shielding coils in a typical six-bus-bars scenario. It turns out that the “all parallel” shielding coils with a 45° starting position have the best shielding performance, whereas the “separated loop” shielding coils with a 0° starting position feature the lowest heating value. Physical experiments were performed, which verified all the models and the conclusions proposed in the paper. In addition, for shielding coils with other than the four-segment configuration, the analysis process will generally be the same.

Design of equivalent coils for anti- interference testing of heavy current transformers

“…The parameters of the sample are given in Table 4. As the mathematical models of the interfering fields, which is the basis of the methodology, have been validated on higher-rated 30 kA HCT [16], we believe the conclusions of the experiment can also be expanded to HCTs with higher current rating.…”

“…There have been attempts to build a mathematical model of the stray field [1,12], and in a recent study [16], the mathematical models of the leakage field produced by coils are also derived. The models have been verified on a 30 kA HCT by physical experiments.…”