This paper describes a new approach for modelling of a distribution transformer and automatic voltage regulator in forward/backward sweep-based algorithms for unbalanced radial distribution systems. For the transformer modelling a symmetrical components model is used and zero sequence voltage and current updating for the sweep-based methods are demonstrated. The validity and effectiveness of the proposed method is demonstrated in a simple two-bus system for grounded wye-delta and delta-grounded wye transformer connections. The automatic voltage regulators (AVRs) are included into the sweep-based methods and tested by using two distribution test systems. From the systems, all results are in agreement, the proposed model is valid and reliable, and the performance of the algorithms is less affected from the inclusion of regulator modelling.
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