ABB REL 356

ABB REL 356 Current Differential Protection
6-5
Computer Communications
*Note that only every third sample is sent from the remote end. The local received value, Vfrr, and the computed, Vfri,
are “padded” in OSCAR by repeating the same sample value three times. This results in a “stepped” waveform. This is
of no concern for the measurement as only every third, true, sample is used for diifferential measurement. The display
Vfrr and Vfri are delayed by the local delay time, LDT plus 3 frames values, i.e. LDT + 3 x 1.39 msec = LDT + 4.17 msec.
The delay is due to data transfer time between the protection processor and the oscillographic processor and is of no
importance for the protection function. For testing, however, it should be noted that when Vfri lags the local quantity, Vfli
by 90 degrees + LDT they are actually in phase, i.e. an internal fault. When Vfri leads Vfli by LDT - 90 degrees they are
actually 180 degrees out of phase, i.e. an external fault.
Digital Signals
A total of 64 digital signals are displayed in OSCAR. These signals are easiest identified by finding them in the
SYSTEM LOGIC diagrams, at the back of this IL.
The first 20 digital signals are display in the OSCAR main screen after downloading the file from the REL 356 relay. The
command F8 - DIG MENU displays 20 additional signals and the command F1 - SCROLL DIGI UP displays the remain-
ing 24 signals, one by one.
Main Screen
PLT pilot trip
SBT stub bus trip
OBKT open breaker trip
ROBR remote open breaker
CT channel trouble
RDPD remote differential protection disabled
RNRM receive in normal mode
RDTT receive direct transfer trip
SCTB soft channel trouble (no delay measurement)
CHOK channel OK
TDIS transmit disable
TRNM transmit in normal mode
OBKR open breaker
LDTT local direct transfer trip input
LDPD differential protection disable input
DEMM DCE echo mismatch
DNOR DCE no response
DRST DCE in reset
DMMM DCE modem mismatch
BK1S breaker 1 trip contact seal
Extended Digital Screen
BK3S breaker 3 trip seal
BK4S breaker 4 trip seal
BK5S breaker 5 trip seal
BL6S breaker 6 trip seal
JMP7 jumper 7
TTRP direct transfer trip
STBB stub bus
DISA disable input
ERST external reset input
52B 52b contact input
TP12 trip relay 1 and 2
TL34 trip relay 3 and 4
TP56 trip relay 5 and 6