VAMP 210
Generator protection relay
Technical description
VAMP Ltd
18
Vamp 24h support phone: +358 (0)20 753 3264
VM210.EN004
2.2.4.
Directional earth-fault protection (67N)
The directional earth fault protection is used in networks
where a sensitive earth fault protection is needed and in
applications with varying network structure and length.
Directional earth fault protection gives also extra selectivity in
case the cable capacitance between CT and generator is
significant. This stage uses the input I
01
for earth fault current
and input U
0
for residual voltage.
For the I
0
and U
0
measurement the fundamental frequency
components are used. In this case the third harmonic is
suppressed with at least 60 dB, which contributes to the
extremely high accuracy of the earth-fault protection.
The stage starts when the resistive component of the earth
fault current exceeds the setting limit and the measured
residual voltage is more than the corresponding setting value.
Figure 2.2.4-2.
If the DI control is selected and DI=0 then the actual operation
characteristic is I
o
Res and if DI=1 it is I
o
Cap.
&
Isin
j
t
&
&
Io
Uo
Icos
j
i0fiislohko
>
>
Start
Trip
Register
event
Register
event
Choice
Icos / Isin
j
j
Setting
I > s
j
Setting
Io > s
Delay
Enable events
Block
Figure 2.2.4-1 Block diagram of the directional earth-fault stage I
0
ϕ
>.
Figure 2.2.4-2 Operation characteristic of the directional I
0
cos
ϕ
.
