UBase shall be entered as rated phase-to-phase voltage of the protected object in
primary kV.
9.14.2.2 Application possibilities
VRPVOC function can be used in one of the following applications:
• voltage controlled over-current
• voltage restrained over-current
In both applications a seal-in of the overcurrent function at under-voltage can be
included by configuration.
9.14.2.3 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 function, the configuration is done according to figure 203. 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
Figure 203: Undervoltage seal-in of current start
Section 9 1MRK 502 071-UEN -
Current protection
396 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
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