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
0.5
s or more) is typically used. Note that the value set is the time between
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
.
BlkLowVolt
: Voltage level under which the internal blocking of the undervoltage stage is
activated; it is set in % of
UBase
. This setting must be lower than the setting
StartVolt
. The
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
UBase
; so it defines the first point of the characteristic
(
VDepFact
*
StartCurr
/100*
IBase
; 0.25*
UBase
).
Step mode
: it is the start level of the
overcurrent stage given in % of
StartCurr
when the voltage is lower than
UHighLimit
/
100*
UBase
.
UHighLimit
: when the measured phase-to-phase voltage is higher than
UHighLimit
/
100*
UBase
, than the start level of the overcurrent stage is
StartCurr
/100*
IBase
. In particular, in
Slope
mode it define the second point of the characteristic (
StartCurr
/100*
IBase
;
UHighLimit
/
100*
UBase
).
7.16.3.2 Voltage-restrained overcurrent protection for generator and step-up
transformer
GUID-263B960B-2280-461C-B455-F17B7D278F60 v8
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
Operation
to
On
2. Set
GlobalBaseSel
to the right value in order to select the Global Base Values Group with
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
Characterist
to match the type of overcurrent curves used in the network
IEC Very
inv.
5. Set the multiplier
k
=
1
(default value).
Section 7 1MRK 511 358-UEN A
Current protection
172
Application manual
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