8.3.7.2
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.
Uref = -3U
0
e
jRCADir
, that is -3U
0
rotated by the set characteristic angle
RCADir
(φ=ang(3I
0
)-ang(U
ref
) ).
RCADir
is normally set equal to 0 in a high impedance
earthed 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.
=
=
0 ,
0
RCADir
ROADir
0
3I
ϕ =
−
0
ref
ang(3I ) ang(3U )
−
=
0
ref
3U
U
0
3I cos
⋅
ϕ
IEC06000648-3-en.vsd
IEC06000648 V3 EN
Figure 100:
RCADir set to 0°
IEC06000649_3_en.vsd
ref
U
= −
=
90 ,
90
RCADir
ROADir
0
3
I
0
3
⋅
ϕ
I cos
ϕ =
−
0
(3 )
(
)
ref
ang I
ang U
−
0
3
U
IEC06000649 V3 EN
Figure 101:
RCADir set to -90°
1MRK 502 048-UEN A
Section 8
Current protection
207
Technical manual
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