Controlled Switching — Buyer´s Guide
F-4
Edition 2, 2006-09
Application Power Transformers
Switching of No-load Power Transformers
420:132 kV, 750 MVA transformer in test area,
Ludvika, Sweden
Control of Closing Operations
Switchsync™ controllers for transformer cir-
cuit breakers are used for control of closing
operations, in order to limit inrush currents.
The closing operation should be initiated at
an appropriate time instant in consideration
to the residual flux of the transformer core.
The goal is to make the flux in the core sym-
metrical from the start. Disregarding residual
flux, the general principles in achieving this
goal may be summarized as:
- The first making should be made in one
phase, if the neutral of the primary wind-
ing is grounded, or in two phases if the
neutral is ungrounded. Making should oc-
cur at maximum phase-to-ground voltage
(grounded neutral) or maximum phase-to-
phase voltage (ungrounded neutral).
- Making of the remaining phase or phases
should occur at an instant when the flux in
the corresponding cores resulting from the
first making is the same as the flux that will
circulate in these cores under steady state
conditions.
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