Functions
6-1597SA522 Manual
C53000-G1176-C119-2
Detection of a sequential fault can be selected to occur either with a
trip command
of
a protection function during the dead time or with every further
fault detection
.
It is possible to select the desired response of the internal automatic recloser follow-
ing the detection of a sequential fault.
a) (9)/702'(
blocks AR
:
The reclosure is blocked as soon as a sequential fault is detected. Tripping as a re-
sult of the sequential fault is three-pole. This applies irrespective of whether three-
pole cycles are permitted or not. There are no further reclosure attempts; the auto-
matic reclosure circuit is blocked dynamically (see also above under subtitle "Re-
close block“, page 154).
b) (9)/702'(
starts 3p AR
:
As soon as a sequential fault is detected the recloser switches over to a three pole
cycle. All trip commands are now three-pole. The separately settable dead time for
sequential faults starts with the clearance of the sequential fault; after the dead time
the circuit-breaker receives a close command. The further sequence is the same as
for single and three-pole cycles.
The complete dead time in this case consists of the portion of the single pole dead
time up to clearance of the sequential fault plus the dead time for the sequential
fault. This makes sence because the duration of the three-pole dead time is most
important for the stability of the network.
If reclosure is blocked due to a sequential fault without the protection issuing a three-
pole trip command (e.g. for sequential fault detection with starting), the device can
send a three pole trip command so that the circuit-breaker does not remain open with
one pole (forced three-pole coupling).
Dead line check
(DLC)
If the voltage of a disconnected phase does not disappear following a trip, reclosure
can be prevented. A prerequisite for this function is that the voltage transformers are
connected on the line side of the circuit breaker. To select this function the dead line
check must be activated. The automatic reclosure function then checks the discon-
nected line for no-voltage: The line must have been without voltage for at least an ad-
equate measuring time during the dead time. If this was not the case the reclosure is
blocked dynamically.
This no-voltage check on the line is of advantage if a small generator (e.g. wind
generator) is connected along the line.
Reduced dead time
(RDT)
If automatic reclosure is performed in connection with time-graded protection, non-
selective tripping before reclosure is often unavoidable in order to achieve fast,
simultaneous tripping at all line ends. The 7SA522 has a "reduced dead time (RDT)"
procedure which reduces the effect of the short-circuit on healthy line sections to a
minimum. The three phase voltages are measured for the reduced dead time. The
voltage transformers must be located on the line side of the circuit breaker.
In the event of a short-circuit close to on of the line ends, the surrounding lines can
initially be tripped because for example a distance protection detects the fault in its
overreaching zone Z1B (figure 6-84, relay location III). If the network is meshed and
there is at least one other infeed on the busbar B, the voltage there returns immedi-
ately after clearance of the fault. For single-pole tripping it is sufficient if there is an
earthed transformer with delta winding connected at busbar B which ensures symme-
try of the voltages and thus induces a return voltage in the open phase. This allows a
distinction between the faulty line and the unfaulted line to be made as follows:
Since line B–C is only tripped singled-ended at C, it receives a return voltage from the
end B which is not tripped so that at C the open phase(s) also has(have) voltage. If
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