TRIPUC, operation of the undercurrent feature
START, current bigger than I> level
STARTUC, current smaller than I< level
LOCKOUT, sealed-in TRIP output signal from the function. Note that lockout feature
is only enabled by setting AutoLockout = “On”
BLKRECL, output signal active as long as Theta > ReclsLevTheta, which can be used
to block closing of the generator CB
Simplified logic diagram for lockout functionality is shown in Figure
224.
AND
TRIP
OR
SETLKOUT
AND
NOT
RESET
AND
BLOCK
LOCKOUT
IEC12000020-1-en.vsd
AutoLockout
IEC12000020 V1 EN
Figure 224: Trip Lockout logic
Alarm ripple detection
The rotor winding is provided with DC excitation current through the rectifier bridge
and the excitation transformer. In case a fault happens in the rectifier circuit, for
example a short circuit or broken diode/thyristor, the rotor system is endangered, due
to asymmetry in the three phase currents. This asymmetry will cause a ripple in the
rotor DC current. This alarm method estimates the ripple of the rotor DC current and
if it exceed the preset level (parameter AlmRippleLev) it will start a timer (defined by
parameter tAlarmRipple). Once this timer has expired the signal ALRIPPLE will be
given.
The service value for the ripple level is provided. It is recommended to check the
natural ripple of the rotor DC current at site before the level for parameter
AlmRippleLev is set. Note that this ripple supervision shall only be used if the rotor DC
current is used as measured quantity.
Section 8 1MRK502052-UEN B
Current protection
474
Technical manual
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