ABB RELION REX640, Technical Manual, Page: 1417 / 1960

excitation faults) to protect the system. The logic for the same has been shown in
Table 1347
and
Table 1348
.
The over/under fueling and over/under excitation logic will be checked
only if the local active and reactive power are above 2% of nominal value
respectively. When the local active and reactive power are less than 2%,
the
OPERATE
output is issued instantaneously.
Table 1347: Criteria for activation of STOP_ENGINE output
Fault type Criteria Output
Over fueling fault
MIN (P1 … P8) <
Min active power
That is, One among the network generators (ex-
cluding the local generator) enter reverse power
OR
F > Max Freq limit + Max Freq deviation
STOP_ENGINE
Under fueling fault (MAX (P1 … P8) >
Max active power
That is, One among the network generators enter
over power region
OR
F <
Min Freq limit
–
Max Freq deviation
)
AND
P < 0.0
That is, local generator enters reverse power zone.
Table 1348: Criteria for activation of DE_EXCITE output
Fault type Criteria Output
Over excitation
fault
MIN(Q1 … Q8) < Min reactive power
OR
Uavg > Max voltage limit + Max Volts deviation
DE_EXCITE
Under excitation
fault
(Uavg < Min voltage limit – Max Volts deviation
OR
I_MAX > 100% of nominal value
I_MAX = Maximum of the three phase currents ob-
tained from input I3P)
AND
Q < 0.0
That is, local generator enters reverse reactive pow-
er zone.
The activation of
STOP_ENGINE
or
DE_EXCITE
outputs, activates the
PRE_TRIP
output and initiates the operate delay timer. The timer characteristic is based on DT.
Once the time set by Operate delay time elapses or when active power (for fueling
1MRS759142 F Condition monitoring functions
REX640
Technical Manual
1417