Functions
2.14 Monitoring Functions
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
168
A wire break is signaled under the following conditions:
• A suspected local wire break has been detected.
• The logic for detecting the circuit-breaker position (see Section 2.16, Detection of the Circuit-Breaker Posi-
tion) does not signal an open circuit-breaker pole. Broken wire detection is not possible if the circuit breaker
is open. If the breaker position cannot be determined, a closed circuit breaker is assumed.
• The ground current is measured on the additional current transformer
I
4
. In this current channel and 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
detected for the affected phases.
• The device at the other end of the protected object must not have signaled 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 protected object may have measured a phase current of more than
2
I
Nom
. 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
criteria
, it is signaled via the protection data in-
terface to the device at the other end of the protected object and leads immediately to a wire break message.
The differential protection functions are blocked as well if this has been configured.
In the event of a local wire break, the device generates the indication „Wire break
I
X
“ (No. 290, 291, 292).
If a wire break is detected at the other end of the protected object, the indication „Wire break at the other end
I
X
“
(No. 297, 298, 299) is generated.
If the broken wire monitoring is disabled, the message 295
„Broken wire OFF“
is output.
The broken wire monitoring is reset by the return of the phase current (
I
Lx
> 0.05
I
Nom
) 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 only works with the local available information. Multi-
pole wire break is not reported in emergency operation.
Note that electronic test devices do not simulate the correct behavior of broken wire so that pickup may occur.
