ABB REG670 Technical Manual page 145

1MRK502052-UEN B
Technical manual
STL1
STL2
STL3
BLK2HL1
BLK2HL2
BLK2HL3
BLK5HL1
BLK5HL2
BLK5HL3
BLKWAVL1
BLKWAVL2
BLKWAVL3
IEC05000279-TIFF V2 EN
Figure 42: Transformer differential protection internal grouping of logical signals
Logic in figures 39, 40,
1. The three fundamental frequency differential currents are applied in a phase-wise
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 start
signal START is set. If the unrestrained limit is exceeded, an immediate
unrestrained trip TRIPUNRE and common trip TRIP are issued.
2. If a start signal is issued in a phase the harmonic and the waveform block signals
are checked. Only a start signal, which is free of all of its block signals can result
in a trip command. If the cross-block logic scheme is applied, then only if all
phases with set start signal are free of their respective block signals, a restrained
trip TRIPRES and common trip TRIP are issued
3. If a start signal is issued in a phase, and the fault has been classified as internal,
then any eventual block signals are overridden and 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 start
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 starts 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
common trip TRIP are issued. This feature is called the sensitive negative
sequence differential protection.
5. If a start signal is issued in a phase (see signal STL1), even if the fault has been
classified as an external fault, the instantaneous differential current of that phase
(see signal IDL1) is analyzed for the 2
OR
OR
OR
OR
41 and 42 can be summarized as follows:
nd
and the 5
Section 6
Differential protection
START
BLK2H
BLK5H
BLKWAV
IEC05000279-2-en.vsd
th
harmonic contents (see the
139