Siemens SIPROTEC 7SC80 Series Manual page 84

Functions
2.3 Directional Overcurrent Protection 67, 67N
Note
When the 67-1 Element or the 67N-1 Element picks up, the phase-specific directional indications „forward" or
„reverse" are generated (indications 2628 to 2636).
Pickup of the 67-2 Element or the 67N-2 Element lies within the parameterized directional range without direc-
tional indication.
Quantity Selection for Direction Determination for the Directional Ground Element
Parameter 1617 67N POLARIZAT. can be set to specify whether direction determination is accomplished
from the zero sequence quantities or ground quantities (with VN and IN) or from the negative sequence
quantities (with V2 and I2). The first option is the preferential setting, the latter is to be selected in case of
danger that the zero voltage be too small due to unfavorable zero impedance or that a parallel line influences
the zero system.
Note
If parameter 213 VT Connect. 3ph is set to Vab, Vbc the direction is always determined using the negative
sequence values V2/I2. For these voltage connection types, the zero sequence voltage (VN or 3V0) is not avail-
able.
67-2 Directional High-set Element (phases)
The pickup and delay of element 67-2 are set at addresses 1502 and 1503. For setting, the same consider-
ations apply as did for the non-directional time overcurrent protection in Section 2.2.6.
The selected time is only an additional time delay and does not include the operating time (measuring time,
dropout time). The delay can be set to ∞. After pickup the Element will then not trip. Pickup, however, will be
signaled. If the 67-2 Element is not required at all, the pickup value 67-2 PICKUP should be set to ∞. For this
setting, there is neither a pickup signal generated nor a trip.
67N-2 Directional High-set Element (Ground)
The pickup and delay of element 67N-2 are set at addresses 1602 and 1603. The same considerations apply
for these settings as did for phase currents discussed earlier.
The selected time is only an additional time delay and does not include the operating time (measuring time,
dropout time). The delay can be set to ∞. After pickup the Element will then not trip. Pickup, however, will be
signaled. If the 67N-2 Element is not required at all, then the pickup value 67N-2 PICKUP should be set to ∞.
This setting prevents from tripping and the generation of a pickup message.
67-1 Directional Overcurrent Element (phases)
The maximum appearing load current is very important for the setting of the overcurrent element 1504 67-1
PICKUP. Pickup due to overload must never occur since in this mode, the device operates as fault protection
with correspondingly short tripping times and not as overload protection. For this reason, lines are set to
approx. 20 % above the maximum expected (over)load and transformers to approx. 40 %.
If the relay is used to protect transformers with large inrush currents, the inrush restraint feature of 7SC80 may
be used for the 67-1 PICKUP element (for more information, see margin heading "Inrush Restraint").
The delay for directional Elements (address 1505 67-1 DELAY) is usually set shorter than the delay for non-
directional Elements (address 1205) since the non-directional Elements overlap the directional elements as
backup protection. It should be based on the system coordination requirements for directional tripping.
84
SIPROTEC, 7SC80, Manual
E50417-G1140-C486-A1, Release date 12.2011