Circuito equivalente de un transformador con regulación

This paper presents a methodology aimed at obtaining and applying the equivalent circuit of a regulating transformer, whose turn ratio can be varied. This aspect is insufficiently treated in most current textbooks in which the equivalent circuit of a tapped transformer is not well justified. This document shows how to obtain the equivalent circuit of the transformer and how to apply it using either physical quantities or per unit (pu) quantities. The usage of per unit values can be performed by selecting the base quantities in an arbitrary manner, which is an obvious advantage when one of the rated voltages must be estimated. Although the goal of the paper is to develop a method for regulating transformers (e.g., under load tap changers, ULTC), it can be applied to transformers with a fixed turn ratio for which one of the rated voltages is unknown. The paper includes two illustrative examples with different fields of application.