Selected Voltage Magnitude
OC1 Stage Pickup Level
PickupCurr_OC1
VDepFact_OC1 *
PickupCurr_OC1
VHighLimit_OC1
en05000323_ansi.vsd
ANSI05000323 V1 EN-US
Figure 374: Example for OC1 step current pickup level variation as function of measured
voltage magnitude in Step mode of operation
This feature will simply change the set overcurrent pickup level in accordance with magnitude
variations of the measured voltage. It shall be noted that this feature will as well affect the pickup
current value for calculation of trip times for IDMT curves (overcurrent with IDMT curve will trip
faster during low voltage conditions).
Current restraint feature
M13751-338 v3
The overcurrent protection step operation can be made dependent of a restraining current
quantity (see table
411). Practically then the pickup level of the overcurrent step is not constant
but instead increases with the increase in the magnitude of the restraining current.
IsetHigh
IsetLow
I
Measured
Restraint
atan(RestrCoeff)
en05000255.vsd
Operate area
I>RestrCoeff*Irestrain
IEC05000255 V1 EN-US
Figure 375: Current pickup variation with restraint current magnitude
This feature will simply prevent overcurrent step to pickup if the magnitude of the measured
current quantity is smaller than the set percentage of the restrain current magnitude. However
this feature will not affect the pickup current value for calculation of trip times for IDMT curves.
This means that the IDMT curve trip time will not be influenced by the restrain current magnitude.
Section 11 1MRK 502 066-UUS B
Multipurpose protection
704
Technical manual
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