Note that it is possible to decide by a parameter setting how the directional feature shall behave
when the magnitude of the measured voltage phasor falls below the pre-set value. User can select
one of the following three options:
• Non-directional (operation allowed for low magnitude of the reference voltage)
• Block (operation prevented for low magnitude of the reference voltage)
• Memory (memory voltage shall be used to determine direction of the current)
It shall also be noted that the memory duration is limited in the algorithm to 100 ms. After that
time the current direction will be locked to the one determined during memory time and it will re-
set only if the current fails below set pickup level or voltage goes above set voltage memory limit.
Voltage restraint/control feature
M13751-326 v4
The overcurrent protection step operation can be made dependent of a measured voltage
quantity (see table
410). Practically then the pickup level of the overcurrent step is not constant
but instead decreases with the decrease in the magnitude of the measured voltage quantity. Two
different types of dependencies are available:
• Voltage restraint overcurrent (when setting parameter
VDepMode_OC1
=
Slope
)
Selected Voltage
Magnitude
OC1 Stage Pickup Level
PickupCurr_OC1
VDepFact_OC1 * PickupCurr_OC1
VHighLimit_OC1VLowLimit_OC1
en05000324_ansi.vsd
ANSI05000324 V1 EN-US
Figure 373: Example for OC1 step current pickup level variation as function of measured
voltage magnitude in Slope mode of operation
• Voltage controlled overcurrent (when setting parameter
VDepMode_OC1
=
Step
)
1MRK 502 066-UUS B Section 11
Multipurpose protection
703
Technical manual
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