resistors, the prefluxing device only operates during the isolation
period and then is removed from the power system prior to
energization.
The “controlled closing with flux measurements” strategy
acquires the residual flux information from the transformer
for consistent performance, but requires additional, permanent
measurement equipment be mounted on the transformer terminals.
The prefluxing device does not require knowledge of the
initial transformer flux since the prefluxing device will set the
transformer flux to the desired polarity. Hence, supplementary
measurement equipment is not needed. In addition, the prefluxing
of the transformer is performed after any measurements
are made on the transformer during maintenance procedures
to ensure the residual flux is at the known polarity prior to the
controlled energization.
The prefluxing method was tested in the lab using a singlephase,
three-winding, 18-kVA, shell-type transformer. Table I
contains the pertinent transformer specifications.