Functions
2.12 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
232
2.12.4
Setting Notes
General Settings
During configuration of the protection function (Section 2.1.1), under address
131
Sens. Gnd Fault
it was
determined with which parameters the ground fault detection is functioning. If address
Sens. Gnd Fault
=
Definite Time
is selected, then the definite-time parameters are available. If
Sens. Gnd Fault
=
Log.
inverse A
is set, a logarithmic inverse characteristic is available. If
Sens. Gnd Fault
=
Log. Inverse
B
is set, a logarithmic inverse characteristic with knee point is active. If
Sens. Gnd Fault
=
User Defined
PU
is selected, a user-specified characteristic can be used for the overcurrent elements 50Ns-1 or 51Ns. The
superimposed high-set element 50Ns-2 is available in all these cases. If this function is not required, then
Disabled
is set. The logarithmic inverse characteristics and user characteristics are only available if under
address
130
the standard measuring method
cos
ϕ
/ sin
ϕ
is set.
The characteristic for determining the direction is set at address
130
S.Gnd.F.Dir.Ch
. It is optional to select
either the standard measurement method
cos
ϕ
/ sin
ϕ
or the
V0/I0
ϕ
mea.
with one sector charac-
teristic.
At address
3101
Sens. Gnd Fault
, the function
ON
or
OFF
can be set to either
ON with GF log
or
Alarm
Only
. If settings
ON
and
ON with GF log
are applied, tripping is also possible, otherwise a fault log is created.
A ground fault log is created for
ON with GF log
and
Alarm Only
. Setting
ON with GF log
is only
available if characteristic
V0/I0
ϕ
mea.
has been selected at address
130
S.Gnd.F.Dir.Ch
.
The parameters
3111
T-DELAY Pickup
and
3130
PU CRITERIA
are only visible if the standard measure-
ment method
cos
ϕ
/ sin
ϕ
has been selected when setting the direction characteristic. The ground fault
is detected and reported when the displacement voltage was sustained a certain time
T-DELAY Pickup
).
Address
3130
PU CRITERIA
specifies whether ground fault detection is enabled only for pickups of V
N
and
I
NS
(
Vgnd AND INs
) or as soon as one of the two has picked up (
Vgnd OR INs
).
The pickup can be stabilized for ground fault protection with definite time curve by a settable dropout time delay
(address
3121
50Ns T DROP-OUT
). This facility is used in power systems with intermittent faults. Used to-
gether with electro-mechanical relays, it allows different dropout responses to be adjusted and time grading of
digital and electro-magnetic relays to be implemented. The setting depends on the dropout time delay of the
electro-magnetic relay. If no coordination is required, the preset value (zero = no dropout time delay) remains.
Note
Address
213
VT Connect. 3ph
specifies how the voltage transformers are connected (phase-to-ground or
phase-to-phase). Furthermore, adjustment factor
Vph / Vdelta
for displacement voltage is properly set in
address
206
, primary and secondary nominal transformer current in the ground path are properly set in ad-
dresses
217
and
218
.
Overcurrent Elements Definite Time/Inverse Time
A two-element current/time characteristic can be set at addresses
3113
to
3120
. These elements operate with
the amounts of the ground current. They are therefore only useful where the magnitude of the ground current
and maybe its direction can be used to specify the ground fault. This may be the case for grounded systems
(solid or low-resistant) or on electrical machines connected to the busbar of an ungrounded power system,
when in case of a network ground fault the machine supplies only a negligible ground fault current across the
measurement location, which must be situated between the machine terminals and the network, whereas in
case of a machine ground fault the total ground fault current produced by the total network is available.
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