Voltage-Restrained Overcurrent Protection For Generator And Step-Up Transformer - ABB Relion REC670 Applications Manual

Section 7
Current protection
tMin : Minimum operation time for all inverse time characteristics. At high currents the inverse
time characteristic might give a very short operation time. By setting this parameter the
operation time of the step can never be shorter than the setting.
Operation_UV : it sets On / Off the operation of the under-voltage stage.
StartVolt : Operation phase-to-phase voltage level given in % of UBase for the under-voltage
stage. Typical setting may be, for example, in the range from 70% to 80% of the rated voltage
of the generator.
tDef_UV : Definite time delay. Since it is related to a backup protection function, a long time
delay (for example
activation 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
setting can be 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 start level of the overcurrent stage given in % of StartCurr
when the voltage is lower than 25% of
VDepFact * StartCurr /100* IBase ; 0.25* UBase ). Step mode : it is the start level of the
(
overcurrent stage given in % of
UBase .
100*
UHighLimit : when the measured phase-to-phase voltage is higher than UHighLimit /
UBase , than the start level of the overcurrent stage is StartCurr /100* IBase . In particular, in
100*
Slope mode it define the second point of the characteristic ( StartCurr /100* IBase ; UHighLimit /
UBase ).
100*
7.16.3.2 Voltage-restrained overcurrent protection for generator and step-up
transformer
An example of how to use VRPVOC 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
• Start current of 185% of generator rated current at rated generator voltage
• Start current 25% of the original start current value for generator voltages below 25% of
rated voltage
To ensure proper operation of the function:
1. Set
2. Set
UBase 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 in the application
configuration.
4. Select
inv.
5. Set the multiplier
172
0.5 s or more) is typically used. Note that the value set is the time between
UBase . This setting must be lower than the setting StartVolt . The
Operation to On
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
k = 1 (default value).
UBase ; so it defines the first point of the characteristic
StartCurr when the voltage is lower than UHighLimit /
1MRK 511 358-UEN A
BlkLowVolt .
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