Siemens siprotec 7SA522, User Manual

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Functions
6-77
7SA522 Manual
C53000-G1176-C119-2
6.4 Distance Protection Teleprotection Schemes
Purpose of Signal
Transmission Short-circuits 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 sec-
tions that are shorter than the smallest sensible distance setting, short-circuits can
also not be selectively 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 from the opposite line end by means of signal transmission systems. For this
purpose, the device has signal send outputs and receive inputs as well as associated
logic functions.
Teleprotection
Methods The distance protection is set with normal zone grading characteristic. An additional
fast overreaching zone Z1B is available for teleprotection schemes. Signal transmis-
sion and trip release methods depend on the teleprotection scheme. At least one re-
verse looking distance zone may be required for some teleprotection schemes. It is
recommended to use zone Z3 for this purpose.
As the distance zones Z1 ... Z5 (without Z1B) function independently, an instantane-
ous trip in Z1 without a release 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.
The 7SA522 permits:
•
Permissive Underreach Transfer Trip with Zone Acceleration Z1B (PUTT)
•
Direct (underreach) Transfer Trip
•
Permissive Overreach Transfer Trip (POTT)
•
Unblocking with Overreach zon Z1B
•
Blocking
Signal Transmis-
sion Channels For the signal transmission, at least one communication channel in each direction is
required. For example, fibre optic connections or voice frequency modulated high fre-
quency channels via pilot cables, power line carrier or microwave radio links can be
used for this purpose.
The 7SA522 also makes provision for the transmission of phase segregated signals.
For this purpose, three transmission channels are required in each direction. The ad-
ditional expense for the signal transmission is weighed up by the advantage that de-
pendable single-pole automatic reclosure can be carried out even when two single-
phase faults occur on different lines in the system.
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
the each of the others in both directions. Phase segregated signal transmission is
however not provided for three terminal line applications.
During disturbances in the receiver or on the transmission path, the teleprotection sup-
plement may be blocked via a binary input, without affecting the normal time graded
distance protection. The measuring reach control (enable zone Z1B) can be obtained
via the binary input “
!(QDEOH$5]RQHVµ
(see also Figure 6-39 above) from an ex-
ternal reclosure device or from the internal automatic reclose function.