Voltage-Restrained Overcurrent Protection For Generator And Step-Up Transformer - ABB Relion 670 Series Applications Manual

1MRK 511 358-UUS A
tDef_UV : Definite time delay. Since it is related to a backup protection function, a long time delay
(for example
of the start and the trip outputs.
EnBlkLowV : This parameter enables the internal block of the undervoltage stage for low voltage
condition; the voltage level is defined by the parameter
BlkLowVolt : Voltage level under which the internal blocking of the undervoltage stage is activated;
it is set in % of
very low, for example, lower than 10%.
VDepMode : Selection of the characteristic of the start level of the overcurrent stage as a function
of the phase-to-phase voltage; two options are available: Slope and Step. See Technical Manual for
details about the characteristics.
VDepFact : Slope mode : it is the pickup level of the overcurrent stage given in % of Pickup_Curr
when the voltage is lower than 25% of
VDepFact * Pickup_Curr /100* IBase ; 0.25* VBase ).
(
Step mode : it is the pickup level of the overcurrent stage given in % of Pickup_Curr when the
voltage is lower than
VHighLimit : when the measured phase-to-phase voltage is higher than VHighLimit /100* VBase ,
than the pickup level of the overcurrent stage is
mode it define the second point of the characteristic (
VBase ).
100*
7.17.3.2 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
2. Set
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
5. Set the multiplier
6. Set
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
Application manual
0.5 s or more) is typically used. Note that the value set is the time between activation
VBase . This setting must be lower than the setting StartVolt . The setting can be
VHighLimit /100* VBase .
Operation to Enabled
GlobalBaseSel to the right value in order to select the Global Base Values Group with
Characterist to match the type of overcurrent curves used in the network IEC Very inv.
k = 1 (default value).
tDef_OC = 0.00 s, in order to add no additional delay to the trip time defined by the
PickupCurr to the value 185%.
BlkLowVolt .
VBase ; so it defines the first point of the characteristic
Pickup_Curr /100* IBase . In particular, in Slope
Pickup_Curr /100* IBase ; VHighLimit /
Section 7
Current protection
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