VHighLimit: when the measured phase-to-phase voltage is higher than VHighLimit/
100*VBase, than the pickup level of the overcurrent stage is Pickup_Curr/100*IBase. In
particular, in Slope mode it define the second point of the characteristic (Pickup_Curr/
100*IBase ; VHighLimit/100*VBase).
9.13.3.2 Voltage-restrained overcurrent protection for generator and step-up
transformer
An example of how to use VRPVOC (51V) function to provide voltage restrained
overcurrent protection for a generator is given below. Let us assume that the time
coordination study gives the following required settings:
• Inverse Time Over Current IDMT curve: IEC very inverse, with multiplier k=1
• Pickup current of 185% of generator rated current at rated generator voltage
• Pickup current 25% of the original pickup current value for generator voltages below
25% of rated voltage
To ensure proper operation of the function:
1. Set Operation to Enabled
2. Set GlobalBaseSel to the right value in order to select the Global Base Values Group
with VBase and IBase equal to the rated phase-to-phase voltage and the rated phase
current of the generator.
3. Connect three-phase generator currents and voltages to VRPVOC (51V) in the
application configuration.
4. Select Characterist to match the type of overcurrent curves used in the network IEC
Very inv.
5. Set the multiplier k = 1 (default value).
6. Set tDef_OC = 0.00 s, in order to add no additional delay to the trip time defined by
the inverse time characteristic.
7. If required, set the minimum operating time for this curve by using the parameter
t_MinTripDelay (default value 0.05 s).
8. Set PickupCurr to the value 185%.
9. Set VDepMode to Slope (default value).
10. Set VDepFact to the value 25% (default value).
11. Set VHighLimit to the value 100% (default value).
All other settings can be left at the default values.
9.13.3.3 Overcurrent protection with undervoltage seal-in
To obtain this functionality, the IED application configuration shall include a logic in
accordance to figure
288 and, of course, the relevant three-phase generator currents and
voltages shall be connected to VRPVOC. Let us assume that, taking into account the
1MRK 506 369-UUS - Section 9
Current protection
Line distance protection REL670 2.2 ANSI 565
Application manual
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