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2 Functions
232
7SD5 Manual
C53000-G1176-C169-1
2.9
Teleprotection for Earth Fault Protection (optional)
2.9.1
General
With the aid of the integrated comparison logic, the directional earth fault protection
according to Section 2.8 can be expanded to a directional comparison protection
scheme.
Transmission
Modes
One of the stages which must be directional
Forward
is used for the directional com-
parison. This stage can only trip fast if a fault is also recognized in the forward direction
at the other line end. A release (unblock) signal or a block signal can be transmitted.
The following permissive schemes exist:
• Directional comparison,
• Directional unblock scheme
and blocking scheme:
• Blocking of the directional stage.
Further stages may be implemented as directional and/or nondirectional backup
stages.
Transmission
Channels
For the signal transmission, one channel in each direction is required. Fibre optic con-
nections or voice frequency modulated high frequency channels via pilot cables,
power line carrier or microwave radio links can be used for this purpose. If the same
transmission channel is used as for the transmission by the distance protection, the
transmission mode must also be the same!
The signal processing can also be used via digital communication lines via a protec-
tion data interface. For example: fibre optic cables, communication networks or dedi-
cated cables (control cable or twisted phone wire). The send and receive signals must
in this case be assigned to fast command channels of the protection data interface
(DIGSI matrix). The direction comparison scheme is suited for these kinds of transmis-
sion:
7SD5 allows also the transmission of phase-selective signals. This presents the ad-
vantage that single-pole automatic reclosure can be carried out even when two single-
phase faults occur on different lines in the system. If no single-phase fault is detected,
signals are transmitted for all three phases. With earth fault protection, phase-segre-
gated transmission only makes sense if the earth faulted phase is identified by means
of the phase selector (address
3109
Trip 1pole E/F
is set to
YES
, refer also to
Section 2.8 under „Tripping“).
The signal transmission schemes are also suited to three terminal lines (teed feeders).
In this case, signal transmission channels are required from each of the three ends to
each of the others in both directions.
During disturbances on the transmission path, the teleprotection supplement may be
blocked. With conventional signal transmission schemes, the disturbance is signalled
by a binary input, with digital communication it is detected automatically by the protec-
tion device.
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