Interaction With Voltage Monitoring; Dynamic Cold Load Pickup Function; Inrush Restraint; Determination Of Direction - Siemens 7SC80 Manual

Interaction with Voltage Monitoring

2.3.6
Spurious tripping might be caused by a measuring voltage failure due to a short circuit, a phase failure in the
voltage transformer secondary system, or a pickup of the voltage transformer mcb (fuse). In the event of a
single-phase or two-phase failure of the measuring voltage, it is possible to recognize this condition and block
the directional overcurrent protection elements (phase and ground) (see logic diagrams).
For additional information on the operation of the voltage transformer monitoring, see Section
urement Supervision

Dynamic Cold Load Pickup Function

2.3.7
It can be necessary to dynamically increase the pickup values of the directional overcurrent protection if
certain system components temporarily consume more power when they are re-energized after a prolonged
dead time. Thus, a general increase of pickup thresholds can be avoided taking into consideration such
starting conditions.
This dynamic cold load pickup function is common to all overcurrent elements and is described in Section
2.4 Dynamic Cold Load
directional and non-directional time overcurrent protection.

Inrush Restraint

2.3.8
The 7SC80 Feeder Protection and Recloser Controller features an inrush current detection which you can acti-
vate separately for each element of the directional overcurrent protection. The function is described in Section
2.12.1 Measurement

Determination of Direction

2.3.9
The determination of the fault direction for the phase directional element and the ground directional element
is performed independently.
Basically, the direction determination is performed by determining the phase angle between the fault current
and a reference voltage.
Method of Directional Measurement
For the phase directional element the fault current of the corresponding phase and the unfaulted phase-
tophase voltage are used as reference voltage. The unfaulted voltage also allows for a correct direction deter-
mination even if the fault voltage has collapsed entirely (short-line fault). In phase-to-ground voltage connec-
tions, the phase-to-phase voltages are calculated. In a connection of two phase-to-phase voltages and V
third phase-to-phase voltage is also calculated.
With three-phase short-line faults, memory voltage values are used to clearly determine the direction if the
measurement voltages are not sufficient.Upon the expiration of the storage time period (2 s), the detected
direction is saved, as long as no sufficient measuring voltage is available. When closing onto a fault, if no
memory voltage values exist in the buffer, the relay element will trip. In all other cases the voltage magnitude
will be sufficient for determining the direction.
For each directional ground element there are two possibilities of direction determination.
Direction Determination with Zero Sequence Calculated or Measured Quantities
For the directional ground fault elements, direction can be determined by comparing the zero sequence
system quantities. In the current path, the Ι
connected to the device. Otherwise, the device calculates the ground current from the sum of the three phase
currents. In the voltage path, the displacement voltage Ι
Otherwise the device calculates as reference voltage the zero sequence voltage 3 · V
three phase voltages. If the magnitude of V
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
Measurement Supervision.
Pickup. The alternative pickup values can be set individually for each element of the
Supervision.
current is valid, when the transformer neutral current is
N
or 3 · V
0
2.3 Directional Overcurrent Protection 67, 67N
is used as reference voltage, if it is connected.
N
is not sufficient to determine direction, the direction is
0
Functions
2.12.1 Meas-
, the
N
from the sum of the
0
121