  In design of new power transformers, reliable and efficient tools are
required to expedite research and development processes. Some of these tools
are used to interpret the data obtained from the transformer tests for better
judgement about the response of the transformer. In this paper a clear
procedure is proposed to estimate the nonlinear relation between flux and
excitation current of power transformers by using online measurable data, which
is the main reason of the input current harmonics. It is shown that the
procedure computes this relation with very high precision and leads to
identical results to that applied in simulation.
