The saved phase-to-ground voltage is used
•
for 1-phase or 3-phase faults
•
up to max. 2 sec. after saving the phasors
•
if there was not pickup before short-circuit occurrence.
The unfaulted phase-to-phase voltage is used
•
for 1-phase faults
•
for unfaulted phase-to-ground voltages
•
if the voltage value is > 70% of the rated voltage.
The negative-sequence system quantities
V
2
and Ι
2
are used
•
for 1-phase or 2-phase faults
•
if Ι
2
> 50 mA and U
2
> 5 V.
When using the negative-sequence system quantities, it is the short circuit with the higher current which
determines the direction in case of two 1-phase short circuits.
If none of the above measured quantities is available, an already existing result of the direction determination
is used or the directional element is blocked for the corresponding phase.
The behavior in the even to a measuring voltage failure can be set. The elements operate directionally or
nondirectionally.
The time overcurrent protection only operates directionally if all 3 phase-to-ground voltages are connected.
Address 144 must be set to connected here.
Directional Characteristic
The directional characteristic of the directional overcurrent elements is fixed. The angle difference φ(
V) - φ(I)
is calculated from the voltage phasors and current phasors using the impedance Z = V/I and the direction is
determined using the depicted directional characteristic.
Functions
2.4 Backup overcurrent
SIPROTEC 4, 7SD80, Manual 77
E50417-G1100-C474-A2, Edition 02.2018
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