OR
PICKUP
Current Check
CB Position Check
AND
t
t1
t
t2
TRRET
TRBU
ANSI18001004-1-en.vsdx
ANSI18001004 V1 EN-US
Figure 277: Simplified overall logic for FollowStart&Mode
The
BuTripMode
setting defines how many measurement elements must operate, when current
criterion is used, to determine if the CB is opened or not:
• 2 elements operate out of three phases and neutral
• 1 element operates out of three phases
• 1 element operates out of three phases and neutral
Note that it is possible to set several timers for the backup trip as described below:
1. Timer
t2
is used when function is started in one phase only (i.e. for single-phase to ground
fault on an OHL (Over Head Lines) when single-pole auto-reclosing is used).
2. Timer
t2MPh
is used when function is started in at least two phases. This will allow to have
shorter backup trip times for a multi-phase fault on an OHL Note that for a protected object
which are always tripped three-phase (e.g. transformers, generators, reactors, cables, etc.)
this timer shall always be set to the same value as
t2
timer.
3. Timer
t3
can be used to give a second backup trip command. It can be used in stations having
small DC battery which is not capable to trip all surrounding breakers at once. Note that
t3
timer will only start when
t2
timer expires.
The
RetripMode
defines how re-trip feature will behave:
•
Off
: The re-trip command to the own circuit breaker is permanently disabled.
•
UseFunctionMode
: Retrip command to the own circuit breaker is given only if measurement
criterion defined by setting parameter
FunctionMode
is still active when set timer
t1
expires
(e.g. if
FunctionMode
=
Current
and current magnitude is higher than set value
IPPU
when
t1
expires, the retrip command will be issued).
•
Always
: Retrip command to the own circuit breaker is given always when set timer
t1
expires
without any further checks.
The simplified logic for the function is given in the following figures.
Section 8 1MRK 502 066-UUS B
Current protection
530
Technical manual
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