where at least two currents (phase current and/or residual current) shall be high for breaker
failure detection.
• The current detection level for the residual current can be set different from the setting of
phase current detection.
• It is possible to have different backup time delays for single-phase faults and for multi-phase
faults.
• It is possible to have instantaneous back-up trip function if the circuit breaker is incapable to
clear faults, for example, at low gas pressure. This will happen when input signal 52FAIL has
logical value one and timer
tCBAlarm
has expired. This situation will be indicated via output
signal CBALARM.
The selection of measurement criterion is done with setting parameter
FunctionMode
, to
determine if the breaker has opened or not:
•
Option1 - Current
: Compares the measured phase current magnitude to setting
IPPU
(operate
phase current level in % of
IBase
), and the measured residual current magnitude to setting IN>
(Operate residual current level in % of
IBase
). Criterion is active (i.e. breaker did not open yet)
if the measured current magnitudes are higher than the set values.
•
Option 2 - CB Pos
: This criterion is active (i.e. breaker did not open yet in phase Lx) if the
binary input CBCLDLx has logical value one. Thus function simply follows the status of CB pole
normally open auxiliary contact (i.e. "52a" or "closed") which shall be connected to this input.
•
Option 3 - Current or CB Pos
: It uses a combination of
Current
or
CB Pos
criteria. Note that
Current
criterion will be then always used, while the
CB Pos
criterion will be only enabled and
used if current is smaller than set value
I>BlkCBPos
at the moment when external INITIATE
signal has been received. It is recommended to set value for
I>BlkCBPos
higher than the set
value for
IPPU
.
By the setting
StartMode
it is possible to select how
t1
and
t2
timers are run and consequently
how output commands are given from the function:
•
Option 1 - LatchedStart
: “By external start signals which is internally latched”.
When function is once started by external INITIATE signal, the timers
t1
and
t2
will always
elapse and then measurement criterion defined by parameter
FunctionMode
will be always
checked in order to verify if the appropriate command shall be given out from the function.
Timers cannot be stopped by removing the external INITIATE signal. Function can be started
again only when all of the following three timers
t1
,
t2
and fixed timer of 150 ms in function
internal design has expired and the measurement criterion defined by parameter
FunctionMode
has been deactivated, see Figure 275.
•
Option 2 - FollowStart
: “Follow the external start signal only”.
The timers
t1
and
t2
will run while external INITIATE signal is present. If they elapse then
measurement criterion defined by parameter
FunctionMode
will be checked in order to verify
if the appropriate command shall be given out from the function. Timers can be always
stopped by resetting the external INITIATE signal, see
Figure 276.
•
Option 3- FollowStart&Mode
: “Follow external start signal and selected
FunctionMode
”.
The timers
t1
and
t2
will run while external INITIATE signal is present and in the same time the
measurement criterion defined by parameter
FunctionMode
is active. If they elapse then the
appropriate command will be given out from the function. Timers can be stopped by resetting
the external INITIATE signal or if the measurement criterion de-activates, see
Figure 277.
Section 8 1MRK 502 066-UUS B
Current protection
528
Technical manual
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