ABB REG650 Technical Manual page 114

Section 6
Differential protection
108
PU_A
PU_B
PU_C
BLK2H_A
BLK2H_B
BLK2H_C
BLK5H_A
BLK5H_B
BLK5H_C
BLKWAV_A
BLKWAV_B
BLKWAV_C
ANSI05000279 V1 EN
Figure 41: Transformer differential protection internal grouping of logical signals
Logic in figures 38, 39, 40
1. The three fundamental frequency differential currents are applied in a phase
segregated manner to two limits. The first limit is the operate-restrain
characteristic, while the other is the high-set unrestrained limit. If the first limit is
exceeded, a pickup signal PICKUP is set. If the unrestrained limit is exceeded, an
immediate unrestrained trip TRIPUNRE and common trip TRIP are issued.
2. If a pickup signal is issued in a phase, then the harmonic-, and the waveform block
signals are checked. Only a pickup signal, which is free of all of its respective
blocking signals, can result in a trip command. If the cross-block logic scheme is
applied, then only if all phases with set pickup signal are free of their respective
block signals, a restrained trip TRIPRES and common trip TRIP are issued
3. If a pickup signal is issued in a phase, and the fault has been classified as internal,
then any eventual block signals are overridden and a unrestrained negative-
sequence trip TRNSUNR and common trip TRIP are issued without any further
delay. This feature is called the unrestrained negative-sequence protection 110%
bias.
4. The sensitive negative sequence differential protection is independent of any
pickup signals. It is meant to detect smaller internal faults, such as turn-to-turn
faults, which are often not detected by the traditional differential protection. The
sensitive negative sequence differential protection pickup whenever both
contributions to the total negative sequence differential current (that must be
compared by the internal/external fault discriminator) are higher than the value of
the setting IMinNegSeq. If a fault is positively recognized as internal, and the
condition is stable with no interruption for at least one fundamental frequency
cycle the sensitive negative sequence differential protection TRNSSENS and
OR
OR
OR
OR
and 41 can be summarized as follows:
1MRK 502 043-UUS B
PICKUP
BLK2H
BLK5H
BLKWAV
en05000279_ansi.vsd
Technical Manual