7.16.2.3 Undervoltage seal-in
GUID-13BE02D3-1322-4075-859B-617CFF608657 v7
In the case of a generator with a static excitation system, which receives its power from the
generator terminals, the magnitude of a sustained phase short-circuit current depends on the
generator terminal voltage. In case of a nearby multi-phase fault, the generator terminal
voltage may drop to quite low level, for example, less than 25%, and the generator fault current
may consequently fall below the pickup level of the overcurrent protection. The short-circuit
current may drop below the generator rated current after 0.5...1 s. Also, for generators with an
excitation system not fed from the generator terminals, a fault can occur when the automatic
voltage regulator is out of service. In such cases, to ensure tripping under such conditions,
overcurrent protection with undervoltage seal-in can be used.
To apply the VRPVOC function, the configuration is done according to figure
78. As seen in the
figure, the pickup of the overcurrent stage will enable the undervoltage stage. Once enabled,
the undervoltage stage will start a timer, which causes function tripping, if the voltage does
not recover above the set value. To ensure a proper reset, the function is blocked two seconds
after the trip signal is issued.
Trip output
OR
OR
t
IEC12000183-1-en.vsd
VRPVOC
I3P*
U3P*
BLOCK
BLKOC
BLKUV
TRIP
TROC
TRUV
START
STOC
STUV
IEC12000183 V1 EN-US
Figure 78: Undervoltage seal-in of current start
7.16.3 Setting guidelines
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GlobalBaseSel
: Selects the global base value group used by the function to define (
IBase
),
(
UBase
) and (
SBase
).
7.16.3.1 Explanation of the setting parameters
GUID-9B777E6D-602B-4214-9170-A44ED2D725BF v3
Operation
: Set to
On
in order to activate the function; set to
Off
to switch off the complete
function.
StartCurr
: Operation phase current level given in % of
IBase
.
Characterist
: Selection of time characteristic: Definite time delay and different types of inverse
time characteristics are available; see Technical Manual for details.
tDef_OC
: Definite time delay. It is used if definite time characteristic is chosen; it shall be set
to
0 s
if the inverse time characteristic is chosen and no additional delay shall be added. Note
that the value set is the time between activation of the start and the trip outputs.
k
: Time multiplier for inverse time delay.
1MRK 511 358-UEN A Section 7
Current protection
171
Application manual
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