2.6 Teleprotection for distance protection
127
7SA522 Manual
C53000-G1176-C155-3
2.6 Teleprotection for distance protection
2.6.1 General
Purpose of Telepro-
tection
Faults which occur on the protected line, beyond the first distance zone, can only be
cleared selectively by the distance protection after a delay time. On line sections that
are shorter than the smallest sensible distance setting, faults can also not be selec-
tively cleared instantaneously.
To achieve non-delayed and selective tripping on 100% of the line length for all faults
by the distance protection, the distance protection can exchange and process infor-
mation with the opposite line end by means of signal transmission schemes. For this
purpose, the device has signal send outputs and receive inputs as well as associated
logic functions. This can be done in a conventional way using send and receive con-
tacts. As an alternative, digital communication lines can be used for signal transmis-
sion (ordering option).
Teleprotection
Schemes
A distinction is made between underreach and overreach schemes.
In underreach
schemes, the protection is set with a normal grading characteristic. If a
trip command occurs in the first zone, the other line end receives this information via
a transmission channel. There the received signal initates a trip, either by activation of
overreach zone Z1B or via a direct trip command.
7SA522 allows:
• Permissive Underreach Transfer Trip with Zone Acceleration Z1B (PUTT),
• Direct (Underreach) Transfer Trip
In overreach
schemes, the protection works from the start with a fast overreaching
zone. This zone, however, can only cause a trip if the opposite end also detects a fault
in the overreaching zone. A release (unblock) signal or a block signal can be transmit-
ted. The following teleprotection schemes are differentiated:
Permissive (release) schemes:
• Permissive Overreach Transfer Trip (POTT) (with overreaching zone Z1B)
• Unblocking with overreaching zone Z1B.
Blocking scheme:
• Unblocking with overreaching zone Z1B.
As the distance zones Z1 ... Z5 (without Z1B) function independently, an instanta-
neous trip in Z1 without a release or blocking signal is always possible. If fast tripping
in Z1 is not required (e.g. on very short lines), then Z1 must be delayed with T1.
Transmission
Channels
For the signal transmission, one channel in each direction is required. For example,
fibre optic connections 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 device is equipped with an optional protection data interface, digital communica-
tion can be used for signal transmission; these include: e.g.: Fibre optic cables, com-
munication networks or dedicated cables.
The following signal transmission schemes are suited for these kinds of transmission:
• Permissive Underreach Transfer Trip with Zone Acceleration Z1B (PUTT),
• Permissive Overreach Transfer Trip (POTT) (with overreaching zone Z1B).
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