2 Functions
176
7SA522 Manual
C53000-G1176-C155-3
2.8 Teleprotection for earth fault overcurrent protection (optional)
2.8.1 General
With the aid of the integrated comparison logic, the directional earth fault protection
according to Section 2.7 can be expanded to a directional comparison protection
scheme.
Transmission
Modes
One of the stages which must be directional )RUZDUG 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!
If the device is equipped with an optional protection data interface, digital communica-
tion lines can be used for signal processing; these include: Fibre optic cables, commu-
nication networks or dedicated lines. The following teleprotection scheme is suited for
these kinds of transmission:
• Directional comparison
7SA522 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. Where the digital protection data
interface is used, the signal transmission is always phase segregated. If no single-
phase fault is recognized, the signals are transmitted for all three phases. Phase-seg-
regated transmission for the earth fault protection is only reasonable if the faulted
phase is detected by the phase selector (address 7ULSSROH() set to <(6,
see also Section 2.7 at “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. Phase segregated transmission is only possible
for three terminal line applications if digital communication channels are used.
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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