ABB RELION 620 Series Technical Manual page 268

Section 4
Protection functions
262
The value for the Min operate voltage setting should be carefully
selected since the accuracy in low signal levels is strongly affected by
the measuring device accuracy.
When the voltage falls below Min operate voltage at a close fault, the fictive voltage
is used to determine the phase angle. The measured voltage is applied again as soon
as the voltage rises above Min operate voltage and hysteresis. The fictive voltage is
also discarded if the measured voltage stays below Min operate voltage and hysteresis
for longer than Voltage Mem time or if the fault current disappears while the fictive
voltage is in use. When the voltage is below Min operate voltage and hysteresis and
the fictive voltage is unusable, the fault direction cannot be determined. The fictive
voltage can be unusable for two reasons:
• The fictive voltage is discarded after Voltage Mem time
• The phase angle cannot be reliably measured before the fault situation.
DPHxPDOC can be forced to the non-directional operation with the NON_DIR input.
When the NON_DIR input is active, DPHxPDOC operates as a non-directional
overcurrent protection, regardless of the Directional mode setting.
GUID-718D61B4-DAD0-4F43-8108-86F7B44E7E2D V1 EN
Figure 125: Operating zones at minimum magnitude levels
1MRS757644 F
620 series
Technical Manual