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The same results are obtained by applying the formulas with the
reference power S
B
´
´
U
I
TN
1
CT
1
=
a
1
S
B
´
´
U
I
TN
2
CT
2
=
a
2
S
B
´
´
U
I
TN
3
CT
3
=
a
3
S
B
A further possibility of compensating different rated powers in the
case of three-winding transformers is to use
the reference values of the A/D channels to match the pro-
·
tection to the different rated currents of c.t's and transformer
factors a1, a2 and a3 to compensate the different powers of
·
the windings.
The "a" factors compensate the signals at the inputs of the dif-
ferential protection.
If the reference values of the A/D channels are changed, the
changes apply to the entire protection system (i.e. all functions
and measured variables).
This can be seen from the following example.
Reference values:
Winding 1:
Winding 2:
Winding 3:
3-40
REG 316*4 1MRB520049-Uen / Rev. F
:
3
´
´
110
250
=
25000
3
´
´
20
600
=
25000
3
´
´
6 3
.
500
=
25000
Reference value =
Reference value =
Reference value =
3
= .
1905
3
= .
0 83
3
=
0 218
.
I
131
TN
1
=
=
0 524
.
I
250
CT
1
I
577
TN
2
=
=
0 962
.
I
600
CT
2
I
458
TN
3
=
=
0 916
.
I
500
CT
3
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