8.16.2.3
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(51V) function, the configuration is done according to figure
. 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
ANSI12000183-1-en.vsd
VRPVOC (51V)
I3P*
I3P*
V3P*
V3P*
BLOCK
BLOCK
BLKOC
BLKOC
BLKUV
BLKUV
TRIP
TRIP
TROC
TROC
27 Trip
27 Trip
PICKUP
PICKUP
PU_OC
PU_OC
27 PU
27 PU
ANSI12000183 V1 EN-US
Figure 94:
Undervoltage seal-in of current pickup
8.16.3
Setting guidelines
GUID-2AE85EC4-669E-47C0-ADD4-3DBA83581096 v2
8.16.3.1
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.
1MRK 511 401-UUS A
Section 8
Current protection
Bay control REC670 2.2 ANSI
237
Application manual
Summary of Contents for Relion REC670
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