Undervoltage Seal-In - ABB REC670 Applications Manual

1MRK 511 401-UUS A
8.16.2.3
8.16.3
8.16.3.1
Bay control REC670 2.2 ANSI
Application manual

Undervoltage seal-in

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
94. 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.
OR
OR
ANSI12000183 V1 EN-US
Figure 94: Undervoltage seal-in of current pickup
Setting guidelines
Explanation of the setting parameters
Operation: Set to On in order to activate the function; set to Off to switch off the
complete function.
VRPVOC (51V)
I3P* TRIP
I3P* TRIP
V3P* TROC
V3P* TROC
BLOCK 27 Trip
BLKOC BLOCK PICKUP 27 Trip
BLKOC PICKUP
BLKUV PU_OC
BLKUV PU_OC
27 PU
27 PU
Section 8
Current protection
GUID-13BE02D3-1322-4075-859B-617CFF608657 v7
Trip output
t
ANSI12000183-1-en.vsd
GUID-2AE85EC4-669E-47C0-ADD4-3DBA83581096 v2
GUID-9B777E6D-602B-4214-9170-A44ED2D725BF v3
237