ABB RELION REX640 Technical Manual page 638

Section 4
Protection functions
632
of two-winding transformer) is close to zero, a fault has most certainly occurred in the
area protected by the differential protection relay. The operating value set for the
instantaneous stage is automatically halved and the internal blocking signals of the
biased stage are inhibited.
Transformer vector group matching
The phase differences of the winding 1 and winding 2 currents (winding 1 and winding
3 in case of a three-winding transformer) that are caused by the vector groups of the
power transformer are numerically compensated in the function.
Phase difference matching is based on the ABB-patented generalized transform-
method. Settings Phase shift Wnd 1-2 and Phase shift Wnd 1-3 determine the current
phase angle difference between windings 1 and 2 and between 1 and 3, respectively.
Normally, the transformer vector group designation includes the winding
configurations and the phase angle difference between given with a clock number. For
example, YNd1 has clock number 1. Settings Phase shift Wnd 1-2 and Phase shift Wnd
1-3 are calculated as clock number ⋅ 30 deg.
Table 591: Examples of Phase shift Wnd 1-2 (and Phase shift Wnd 1-3) settings for some
common vector groups
Vector group between windings 1 and 2 (or windings
1 and 3)
YNd1, Yd1, Dyn1, Dy1
YNd5, Yd5, Dyn5, Dy5
YNd7, Yd7, Dyn7, Dy7
YNd11, Yd11, Dyn11, Dy11
The vector group matching can be set in the resolution of 0.1 degrees, which allows for
cycloconverter applications with a phase angle difference of, for example, 7.5 degrees
between windings.
The Phase Ref winding setting is used to define which of the windings is the reference.
The phase reference can be selected from Phase Ref winding as "Winding 1",
"Winding 2" or "Winding 3". The currents in the winding selected as the phase
reference are not modified (except the removal of the zero-sequence current if set
active) when the currents in other windings are matched with the reference winding (if
the set phase shift between the windings is not zero).
The Phase Ref winding setting does not affect settings Phase shift
Wnd 1-2 and Phase shift Wnd 1-3.
Zero-sequence component elimination
If a wye-connected power transformer neutral is earthed, or if there is a separate
earthing transformer inside the differential protection zone, any out-of-zone earth
Phase angle
30°
150°
210°
330°
1MRS759142 C
REX640
Technical Manual