ABB Relion Technical Manual page 122

Section 6
Differential protection
116
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 the harmonic and the waveform block signals
are checked. Only a pickup signal, which is free of all of its 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
OR
OR
OR
OR
and 41 can be summarized as follows:
1MRK 502 048-UUS A
PICKUP
BLK2H
BLK5H
BLKWAV
en05000279_ansi.vsd
Technical manual