1 2 3 4 A - SIPROTEC

Functions
2.1 General
Special Considerations on Auto-Transformers
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As mentioned above, the common windings on auto-transformers must always be defined as S1 and S2. A third
side may be present if the compensation winding is dimensioned as power winding (tertiary winding) and
accessible (figure 2-5). In this example we have 3 sides and 4 assigned measuring locations. During
parametrization of the auto-transformer, one must always start with the auto-winding.
Figure 2-5 Topology of an auto-transformer with a compensation winding which is used as tertiary winding
Sides:
S1 High voltage side of the main protected object (auto-transformer)
S2 Low voltage side of the main protected object (auto-transformer)
S3 Tertiary winding side (accessible compensation winding) of the main protected object
Measuring locations 3-phase, assigned:
M1 Measuring location, assigned to the main protected object, side 1
M2 Measuring location, assigned to the main protected object, side 1
M3 Measuring location, assigned to the main protected object, side 2
M4 Measuring location, assigned to the main protected object, side 3
A further tap of the winding can also be used as the third side. Be aware that the numbering sequence always
starts with the auto-connected winding: full winding, taps, and then accessible delta winding if required.
Auto-Transformer Banks
If three single-phase auto-transformers are arranged as a power transformer bank, the connections of the starpoint
leads of the auto-windings are accessible and often provided with current transformers. During configuration
of the functional scope in section 2.1.3 you have decided whether a differential protection must be realised
via the entire transformer bank, or whether you prefer a current comparison via the winding of each phase
by means of current law.
Differential protection over the entire power transformer bank:
Regarding the first case, figure 2-6 gives an example of a 3-phase presentation. In this example we have 3
sides and 3 assigned three-phase measuring locations. The auto-connected winding terminals form the sides
S1 (full winding) and S2 (tap) with the assigned 3-phase measuring locations M1 and M2. As the delta winding
functions both as the tertiary winding and the compensation winding, it is the third side S3 with measuring
location M3.
SIPROTEC, 7UT6x, Manual
C53000-G1176-C230-2, Release date 06.2012