ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-44
Group of connection of a three-phase transformer s1, s2, s3
Factor s1 defines the connection of the three phase windings 1.
Factors s2 and s3 define the group of connection of windings 2
and windings 3 respectively, i.e. they define firstly how the
windings are connected and secondly their phase-angle referred
to windings 1.
The following arrangement is an example for two generators with
a common step-up transformer:
1
2
3
Y
d11
d11
HEST 905 004c C
The factors are correspondingly:
s1 = Y
s2 = d11
s3 = d11
Factors s2 and s3 are defined according to their phase shift in
relation to the HV side, i.e. to windings 1.
Note:
This setting for the vector group (s2 = d11, s3 = d11) assumes
that in relation to the protected unit, the star-point is symmetri-
cally formed and grounded on the secondary side of the main
c.t’s.
Should this not be possible for some reason (e.g. plant require-
ments), the group of connection has to be compensated.
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