ABB RELION 670 Series Technical Manual page 148

Section 6
Differential protection
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-US
Figure 45: Transformer differential protection internal grouping of logical signals
Logic in figures 42, 43,
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 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 block 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 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
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 pickup signal is issued in a phase (see signal PU_A), even if the fault has been classified as
an external fault, then the instantaneous differential current of that phase (see signal ID_A) is
analyzed for the 2
Harmonic; Wave block and 5th Harmonic). If there is less harmonic pollution than allowed by
the settings
5th harmonic is 0) then it is assumed that a minor simultaneous internal fault must have
occurred. Only under these conditions a trip command is allowed (the signal TRIPRES_A is = 1).
The cross-block logic scheme is automatically applied under such circumstances. (This means
142
OR
OR
OR
OR
44 and 45 can be summarized as follows:
IMinNegSeq . If a fault is positively recognized as internal,
nd th
and the 5 harmonic contents (see the blocks with the text inside: 2nd
I2/I1Ratio , and I5/I1Ratio , (then the outputs from the blocks 2nd harmonic and
1MRK 502 066-UUS B
PICKUP
BLK2H
BLK5H
BLKWAV
en05000279_ansi.vsd
Technical manual