Siemens SIPROTEC 4 7UT6 Series Manual page 47

[topologie-transformatorbank-tertiaer-ausgleich-020603-st, 1, en_GB]
Figure 2-6
Sides:
S1 High voltage side of the auto-connected winding of the main protected object
S2 Low voltage side (tap) of the auto-connected winding of the main protected object
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 2
M3 Measuring location, assigned to the main protected object, side 3
Auxiliary measuring locations, 1-phase, assigned to the main object (current sum of the CT set)::
X3 Measuring location, assigned to the main protected object, side 1 and 2
Current comparison for common winding of an auto-transformer:
If during configuration of the functional scope in Section
via each winding has been selected, then the example of
terminals of the sides S1 (full winding) and S2 (tap) with the assigned 3-phase measuring locations M1 and
M2, one more side S3 is defined at the starpoint terminals with the 3-phase measuring location M3. In this
way, a current comparison can be realised over each of the three transformer windings, i.e. each phase with
its 3 measuring locations.
Such current comparison is more sensitive to 1-phase earth faults in one of the transformers than the normal
differential protection. This has a certain importance considering that 1-phase earth faults are the most prob-
able faults in such banks. By means of the parameter setting at address 105 PROT. OBJECT = Autotransf.
Autotr. node, the current comparison protection of the auto-transf. node is supported.
On the other hand, the compensation winding cannot and must not be included into this protection even if it
is accessible and equipped with current transformers. This application variant is based on the current law in
that all currents flowing in to a winding must total to zero. In auto-transformers with stabilising winding, the
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
Topology of a transformer bank consisting of 3 single-phase auto-transformers with compen-
sation winding dimensioned as accessible tertiary winding
2.1.3 Functional Scope a pure current comparison
Figure 2-7 applies. Besides the common winding
Functions
2.1 General
47