ABB Relion 670 series, Technical Reference Manual

Page: 444 / 1232

7.6.2 Principle of operation
7.6.2.1 Function inputs
The function is using phasors of the residual current and voltage. Group signals I3P
and V3P containing phasors of residual current and voltage is taken from pre-processor
blocks.
The sensitive directional ground fault protection has the following sub-functions
included:
Directional residual current protection measuring 3I
0
·cos φ
φ is defined as the angle between the residual current 3I
0
and the reference voltage.
Vref = -3V
0
e
jRCADir
, that is -3V
0
rotated by the set characteristic angle RCADir
(φ=ang(3I
0
)-ang(V
ref
) ). RCADir is normally set equal to 0 in a high impedance
grounded network with a neutral point resistor as the active current component is
appearing out on the faulted feeder only.
RCADir is set equal to -90° in an isolated
network as all currents are mainly capacitive. The function operates when 3I
0
·cos φ
gets larger than the set value.
-3V
0
=V
ref
3I
0
RCA = 0
°,
ROA = 90
°
= ang(3I
0
) - ang(3V
ref
)
3I
0
cos
en06000648_ansi.vsd
V
ref
ANSI06000648 V1 EN
Figure 218: RCADir set to 0°
Section 7
1MRK505222-UUS C
Current protection
438
Technical reference manual