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
294. 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 294: Undervoltage seal-in of current pickup
9.17.3 Setting guidelines
GUID-2AE85EC4-669E-47C0-ADD4-3DBA83581096 v2
9.17.3.1 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.
Pickup_Curr: 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
Section 9 1MRK 504 163-UUS A
Current protection
608 Transformer protection RET670 2.2 ANSI
Application manual
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