2 Functions
202
7SD610 Manual
C53000-G1176-C145-4
Broken Wire Moni-
toring
During steady-state operation the broken wire monitoring registers interruptions in the
secondary circuit of the current transformers. In addition to the hazardous potential
caused by high voltages in the secondary circuit, this kind of interruptions simulates
differential currents to the differential protection, such as those evoked by faults in the
protected object.
The broken wire monitor scans the local currents of all three phases, as well as the
differential and stabilization current values of the differential protection transferred
from the devices to the other ends of the protected object. With these values, the
device decides whether there is a broken wire or a network process.
The local wire break detection generates a „Suspected wire-break“ finformation for a
phase when the current abruptly drops to zero during operation. This information con-
tinues to be used if currents and voltage (if connected) in the local device and the cur-
rents in the other devices do not change
In the local device, the „Wire break ILx“ (no. 290, 291, 292) message is generated and
the differential protection is blocked. By transmitting the „Suspected wire-break “ infor-
mation to the other devices, the differential protection is blocked also in these devices
and the „Wire-break at the other end ILx“ (no. 297, 298, 299) message is generated.
If the communication between the devices is disturbed, the device operates in emer-
gency operation. The differential protection is not active. The wire break detection then
operates only with the locally available information. Multipole wire break is not indicat-
ed in emergency operation.
The blocking is cancelled as soon as the device is again supplied with current in the
relevant phase. It is also suppressed when a high fault current is registered by any
device at another end of the protected object.
It has to be observed that electronic test devices do not simulate the correct behaviour
of broken wire so that pickup may occur.
Note
Broken wire monitoring can operate properly only when the fourth current input (I
4
) of
the relay is fed the residual current from a separate current transformer of the protect-
ed line, or no residual current at all.
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