ABB REG316 4 Series Operating Instructions Manual page 74

ABB Switzerland Ltd
I
D
I
N
1
0,75
0,5
0,25
g
0 1
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:
I I
1 2
= = a
4 1
I I
N N
-I 2
I
I = I + I = I 4 -
D
1 2 N
I = I ´ I ´ cos
H 1 2
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.
3-36
REG 316*4 1MRB520049-Uen / Rev. F
b
I
H
2
I
N
=
0
1 I
2 I
HEST 905 003f C
I = I 3
N N
a = I 4 ´ I 1 ´ 1 = I 2
N N
HEST 905 003e C
N