8.10.6 Monitored data
Table 152: VRPVOC Monitored data
Name
Type Values (Range) Unit Description
IMAX REAL - A Maximum phase current
magnitude
UUMIN REAL - kV Minimum ph-to-ph
voltage magnitude
8.10.7 Operation principle
8.10.7.1 Measured quantities
The voltage-restrained time overcurrent protection VRPVOC function is always
connected to three-phase current and three-phase voltage input in the configuration
tool (ACT), but it will always measure the maximum of the three-phase currents and
the minimum of the three phase-to-phase voltages.
8.10.7.2 Base quantities
GlobalBaseSel: Selects the global base value group used by the function to define
(IBase), (UBase) and (SBase).
IBase shall be entered as rated phase current of the protected object in primary
amperes.
UBase shall be entered as rated phase-to-phase voltage of the protected object in
primary kV.
8.10.7.3 Overcurrent protection
The overcurrent step simply compares the magnitude of the measured current quantity
with the set start level. The overcurrent step starts if the magnitude of the measured
current quantity is bigger than the set level.
Voltage restraint/control feature
The overcurrent protection operation is made dependent of a measured voltage
quantity. This means that the start level of the overcurrent step is not constant but
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 = Slope)
Section 8 1MRK 502 048-UEN A
Current protection
252
Technical manual
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