ABB REG316 4 Series - Page 74

ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-36
g
0
0,75
0,25
2
1
1
0,5
b
HEST 905 003e C
I
D
I
N
I
H
N
I
Fig. 3.5.1.3 Operating characteristic of the transformer differ-
ential protection for low through-fault currents
This characteristic provides higher sensitivity for the detection of
faults in the protection zone.
Example:
Internal fault and rated current flowing through the transformer:
01
I
I
4
I
I
N
2
N
1
=a==
2
I
I
HEST 905 003f C
1
I
-I
2
NNN21H
NNN21
I21I1I4cosIII
I3II4III
=´´=a´´=
=-=+=
D
Internal faults will thus be reliably detected when a through-cur-
rent is flowing even at the highest setting for “v”.
Increased basic setting g-High
The increased basic setting g-High has been provided as a
means of preventing false tripping under particular operating
conditions. It is activated by an external signal.