Magnetics for neutral current compensation in three-phase four-wire distribution system

Abstract

In this paper, a number of methods for neutral current compensation using magnetics are proposed and these are compared with reported techniques. The proposed neutral current mitigation techniques include a Scott-transformer, T-connected transformer, star-hexagon transformer and starpolygon transformer designed for mmf (magneto motive force) balance. These transformer configurations along with the conventional transformer configurations such as a star-delta transformer and a zig-zag transformer are analysed, designed, simulated and verified by developing prototypes. The transformers provide a path to the zero sequence fundamental as well as harmonics currents. Two single phase transformers are required for the proposed Scott-connection and T-connection where as three single phase transformers are required in other methods. The neutral current compensation schemes using transformers are modeled and simulated using MATLAB with its Simpower systems (SPS) toolboxes and compared to demonstrate the effectiveness of the proposed transformers. Laboratory prototypes of the transformers are developed and their test results are presented to validate the design of transformers for neutral current compensation.