Live Busbar And Dead Line - GE MiCOM P40 Agile Technical Manual

Application Notes
MiCOM P40 Agile P442, P444
close signal is applied into the logic as a pulse to ensure that an operator cannot simply keep
the close signal applied and wait for the system to come into synchronism. This is often
referred to as guard logic and requires the close signal to be released and then re-applied if
the closure is unsuccessful.
The check synchronism element provides two 'output' signals which feed into the manual CB
control and the auto reclose logic respectively. These signals allow reclosure provided that
the relevant check synchronism criteria are met.
Note that if check-synchronisim is disabled, the DDB: 'Check synch. OK' signal is
automatically asserted and becomes invariant (logical state always forced to 1).
For an interconnected power system, tripping of one line should not cause a significant shift
in the phase relationship of the busbar and line side voltages. Parallel interconnections will
ensure that the two sides remain in synchronism, and that autoreclosure can proceed safely.
However, if the parallel interconnection(s) is/are lost, the frequencies of the two sections of
the split system will begin to slip with respect to each other during the time that the systems
are disconnected. Therefore, a live busbar / live line synchronism check prior to reclosing the
breaker ensures that the resulting phase angle displacement, slip frequency and voltage
difference between the busbar and line voltages are all within acceptable limits for the
system. If they are not, closure of the breaker can be inhibited.
The SYSTEM CHECKS menu contains all of the check synchronism settings for auto ("A/R")
and manual ("Man") reclosure.
• If SOTF is disabled in S1, a dedicated PSL must be created using Deb B (live line or
live bus/dead line) – live/live cannot be managed – in that case.
Note that the combination of the Diff Phase and Bus-Line Delay settings can also be equated
to a differential frequency, as shown below:
• Diff Phase angle set to +/-20°, Bus-Line Delay set to 0.2 s.
• The phase angle 'window' is therefore 40°, which corresponds to 40/360ths of a
cycle = 0.111 cycle. This equates to a differential frequency of:
Therefore it is essential that the time delay chosen before an "in synchronism" output can be
given is not too long, otherwise the synchronising conditions will appear more restrictive than
the actual Diff Frequency setting.
The Live Line and Dead Line settings define the thresholds which dictate whether or not the
line or bus is determined as being live or dead by the relay logic. Under conditions where
either the line or bus is dead, check synchronism is not applicable and closure of the breaker
may or may not be acceptable. Therefore, setting options are provided which allow for both
manual and auto-reclosure under a variety of live/dead conditions. The following paragraphs
describe where these may be used.
WARNING:
If the live line threshold has been set too high, the relay will never detect a healthy network
(as the line voltage is always measured below the voltage threshold). Without the live line
condition, the distance protection cannot use the delta algorithms as no pre-fault detection
has been previously made.
5.9.1

Live Busbar and Dead Line

Where a radial feeder is protected, tripping the circuit breaker will isolate the infeed, and the
feeder will be dead. Provided that there is no local generation which can backfeed to
energise the feeder, reclosure for live busbar / dead line conditions is acceptable. This
setting might also be used to allow re-energisation of a faulted feeder in an interconnected
power system, which had been isolated at both line ends. Live busbar / dead line reclosing
allows energising from one end first, which can then be followed by live line / live busbar
reclosure with voltages in synchronism at the remote end.
0.111 / 0.2 = 0.55 Hz
Voltage setting is always calculated in phase to ground – even if
phase/phase ref has been selected.
P44x/EN AP/Hb6
(AP) 5-143