REG 316*4 1MRB520049-Uen / Rev. F ABB Switzerland Ltd
3-101
Characteristic angle
Determining the phase-angle of the current provides an addi-
tional criterion for preserving discrimination compared with non-
directional overcurrent protection. The directional sensitivity is
±180° in relation to the reference voltage. This is illustrated in the
following diagrams. The angles given apply for connection ac-
cording to the connections in Section 12.
U
ST
I
R
U
R
U
S
U
T
U
RS
U
ST
U
TR
I
R
j
a
= 45°
Operation:
L
L
w
M
a
x
.
s
e
n
s
i
t
i
v
i
t
y
Restraint:
ja
’
cos ( - ) = neg.
j
’
ja
’
cos ( - ) = pos.
HEST 005 001 C
b)a)
j’ = phase-angle between current and voltage
(positive angle)
a = Characteristic angle
L = Border line between operating and restraint areas
a) Definition of current
and voltage
b) Operating characteristic
Fig. 3.5.8.2 Vector diagram for a fault in the forwards direction on
R phase
The function determines the power direction by measuring the
phase-angle of the current in relation to the opposite phase-to-
phase voltage. Which current is compared with which voltage
can be seen from the following table.
Current input Phase-to-neutral voltage Calculated voltage
I
R
U
S
, U
T
U
ST
= U
S
- U
T
I
S
U
T
, U
R
U
TR
= U
T
- U
R
I
T
U
R
, U
S
U
RS
= U
R
- U
S
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