ABB REG316 4 Series - Page 78

ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-40
The same results are obtained by applying the formulas with the
reference power S
B
:
a
UI
S
TN CT
B
1
3
110 250 3
25000
1905
11
=
´´
=
´´
= .
a
UI
S
TN CT
B
2
3
20 600 3
25000
083
22
=
´´
=
´´
= .
a
UI
S
TN CT
B
3
3
6 3 500 3
25000
0 218
33
=
´´
=
´´
=
.
.
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:
Reference value == =
I
I
TN
CT
1
1
131
250
0 524.
Winding 2:
Reference value == =
I
I
TN
CT
2
2
577
600
0 962.
Winding 3:
Reference value == =
I
I
TN
CT
3
3
458
500
0 916.