ABB Relion REC615, Техническое руководство

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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.
(F)DPHxPDOC can be forced to the non-directional operation with the
NON_DIR
input. When the
NON_DIR
input is active, FDPHLPDOC and DPHHPDOC operate as a
non-directional overcurrent protection, regardless of the
Directional mode setting.
Figure 121: Operating zones at minimum magnitude levels
Level detector
The measured phase currents are compared phasewise to the set
Start value. If the
measured value exceeds the set
Start value, the level detector reports the exceeding
1MRS758755 C Protection functions
REC615 & RER615
Technical Manual
239