Modelling and analysis of asymmetrical three-phase distribution transformer banks with mid-tap connected to the secondary neutral conductor

This paper presents phase co-ordinate models for five asymmetrical three-phase distribution transformer banks with mid-tap connected to the secondary neutral conductor. On the basis of the proposed models, these three-phase transformer banks are investigated in this paper. To simplify the derivation of the proposed models, the network-overlapping technique was used. The major considerations in the derivations include copper and core losses,phase angular displacement between primary and secondary voltages, and off-nominal tapping. Using appropriate three-phase power-flow programs or commercial simulation software, the inherent characteristics of these five specific transformer banks under a steady-state condition could be correctly retrieved. The comparison of results of field tests and computer simulations have demonstrated the correctness of these proposed models. The models are of value to distribution engineers for improving the simulation accuracy of a distribution system especially under unbalanced circumstances. (C) 2000 Elsevier Science S.A. All rights reserved.