ABB REG650 Technical Manual page 92

Section 6
Differential protection
86
For the phase reference, the highest voltage wye (Y) connected winding is used. For
example, if the power transformer is a Yd1 power transformer, the HV winding (Y) is
taken as the phase reference winding. If the power transformer is a Yy0 power
transformer the HV winding (Y) is taken as the phase reference winding. If the power
transformer is a Dy1, then the LV winding (y) is taken for the phase reference. If there
is no wye connected winding, such as in Dd0 type of power transformers, then the HV
delta winding (D) is automatically chosen as the phase reference winding.
The fundamental frequency differential currents are in general composed of currents of
all sequences, that is, the positive-, the negative-, and the zero-sequence currents. If the
zero-sequence currents are eliminated (see section
currents"), then the differential currents can consist only of the positive-, and the negative-
sequence currents. When the zero-sequence current is subtracted on one power
transformer side, then it is subtracted from each individual phase current.
Table 27 summarizes the values of the matrices for all standard phase shifts between
windings.
Table 27: Matrices for differential current calculation
Matrix for Reference Winding
Matrix for winding with 30°
lagging
Matrix for winding with 60°
lagging
Matrix for winding with 90°
lagging
Table continues on next page
"Elimination of zero sequence
Matrix with Zero Sequence
Reduction set to On
é - - ù
2 1 1
1 ê ú
× - -
1 2 1
ê ú
3
ê ú
- -
ë 1 1 2 û
(Equation 3)
EQUATION1227 V1 EN
é ù
1 -1 0
1 ê ú
× -
0 1 1
ê ú
3
ê ú
-
ë 1 0 1 û
(Equation 5)
EQUATION1229 V1 EN
-
é ù
1 2 1
1 ê ú
× -
1 1 2
ê ú
3
ê ú
-
2 1 1
ë û
(Equation 6)
EQUATION1230 V1 EN
é ù
0 -1 1
1 ê ú
× -
1 0 1
ê ú
3
ê ú
-
ë 1 1 0 û
(Equation 8)
EQUATION1232 V1 EN
1MRK 502 043-UUS B
Matrix with Zero Sequence
Reduction set to Off
é ù
1 0 0
ê ú
0 1 0
ê ú
ê ú
ë 0 0 1 û
(Equation 4)
EQUATION1228 V1 EN
Not applicable. Matrix on the left
used.
-
é ù
0 1 0
ê ú
-
0 0 1
ê ú
ê ú
-
ë 1 0 0 û
(Equation 7)
EQUATION1231 V1 EN
Not applicable. Matrix on the left
used.
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