Functions
2.11 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
197
In meshed or looped systems, the measuring points of the faulty line also receive the maximum ground fault
current (residual current). Only in this line, "forward" direction is signaled at both ends (Figure 2-72). The rest
of the direction indications in the system may also be useful for ground fault detection. However, some indica-
tions may not be given when the ground current is too low.
Figure 2-72 Determination of the ground fault location basing on directional indicators in the meshed
system
2.11.4 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 = User
Defined PU is selected, a user-specified Curve can be used for the overcurrent elements 50Ns-1 or 51Ns.
The superimposed high-current element 50Ns-2 is available in all these cases. If this function is not required,
then Disabled is set. The user characteristics are only available, if the standard measurement procedure cos
ϕ / sin ϕ has been set at address 130.
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 character-
istic.
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.
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