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Functions
2.24 Monitoring Functions
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
423
A wire break is signalled under the following conditions:
• A suspected local wire break has been detected.
• The logic for detecting the circuit breaker position (see Section 2.25.1, Detection of the Circuit Breaker Po-
sition) does not signal an open circuit breaker pole. Wire break detection is not possible if the circuit breaker
is open. If the breaker position cannot be determined, a closed circuit breaker is assumed.
• In all voltage channels, no jump must have been detected. Jumps in these channels indicate a genuine
power system fault.
• In the other current channels, there must have been no jump without wire break detection. Jumps in the other
current channels also suggest a power system fault, except if a suspected local wire break has been detect-
ed for the affected phases.
• The other devices of the protection constellation must not have signalled a jump. The jump information is
transferred together with the differential protection measurements, so that this information is available simul-
taneously with the first run of the differential protection after the jump.
• In the phase, none of the devices of the protection constellation may have measured a phase current of
more than 2
I
N
. A phase current of such a magnitude is a certain indicator of a power system fault.
When a wire break has been detected according to the above critera, it is signalled via the protection data in-
terface to the other devices of the constellation, and leads immediately to a wire break message. The differen-
tial protection functions are blocked as well if this has been configured.
A local wire break generates the message „Wire break
I
Lx
“ (No. 290, 291, 292), the detection of a wire break
in another device generates the message „Wire break at the other end
I
Lx
“ (No. 297, 298, 299). If the broken
wire monitoring is disabled, the message295 „Broken wire OFF“ is output.
The broken wire monitoring is reset by the return of the phase current (
I
Lx
> 0.05
I
N
) or by the binary input
message 3270 „>RESET BW“ . In 1-1/2 circuit breaker arrangements, the function can only be reset by the
binary input message because the current magnitude is no reliable criterion for a reset of the broken wire mon-
itoring.
If the communication between the devices is disturbed, the device operates in emergency operation. The dif-
ferential protection is not active. The wire break detection then operates only with the locally available informa-
tion. Multipole wire break is not indicated in emergency operation.
It has to be observed that electronic test devices do not behave like a circuit breaker so that pickup can occur
during such tests.