Application Scope - Siemens SIPROTEC 7SA522 Manual

1 Introduction
1.2

Application Scope

Protective Ele-
ments
22
The digital distance protection SIPROTEC
tion for overhead lines and cables with single- and multi-ended infeeds in radial, ring
or any type of meshed systems of any voltage levels. The network neutral can be
earthed, compensated or isolated.
The device incorporates the functions which are normally required for the protection
of an overhead line feeder and is therefore capable of universal application. It may
also be applied as time-graded back-up protection to all types of comparison protec-
tion schemes used on lines, transformers, generators, motors and busbars of all
voltage levels.
The devices located at the ends of the protected zone exchange measuring informa-
tion via teleprotection functions with conventional connections (contacts) or via optio-
nal protection data interfaces using dedicated communication links (usually fibre optic
cables) or a communication network. If the 7SA522 devices are equipped with a pro-
tection data interface, they can be used for a protection object with 2 ends. Lines with
three terminals (teed feeders) require at least one device with two protection data in-
terfaces.
The basic function of the device is the recognition of the distance to the fault with dis-
tance protection measurement. In particular for complex multiphase faults, the dis-
tance protection has a non-switched 6-impedance-loops design (full scheme). Differ-
ent pickup schemes enable a good adaption to system conditions and the user
philosophy. The network neutral can be isolated, compensated or earthed (with or
without earth current limiting). The use on long, heavily-loaded lines is possible with
or without series compensation.
The distance protection may be supplemented by teleprotection using various signal
transmission schemes (for fast tripping on 100 % of the line length). In addition, an
earth fault protection for high resistance earth faults (ordering option) is available,
which may be directional, non-directional and may also be incorporated in signal
transmission. On lines with weak or no infeed at one line end, it is possible to achieve
fast tripping at both line ends by means of the signal transmission schemes. Subse-
quent to energizing the line onto a fault which may be located along the entire line
length, it is possible to achieve a non-delayed trip signal.
In the event of a failure of the measured voltages due to a fault in the secondary cir-
cuits (e.g. trip of the voltage transformer mcb or a fuse) the device can automatically
revert to an emergency operation with an integrated overcurrent protection, until the
measured voltage again becomes available. This time overcurrent protection has
three definite-time overcurrent stages and one inverse-time stage; a number of char-
acteristics based on various standards is available for the inverse-time stage. The
stages can be combined in any way. Alternatively, the time delayed overcurrent pro-
tection may be used as back-up time delayed overcurrent protection, i.e. it functions
independent and parallel to the distance protection.
Depending on the version ordered, most short-circuit protection functions may also trip
single-pole. They may work in co-operation with an integrated automatic reclosure
(available as an option) which enables single-pole, three-pole or single and three-pole
automatic reclosure as well as several interrupt cycles on overhead lines. Before re-
closure after three-pole tripping, the device can check the validity of the reclosure
through voltage and/or synchronism check (can be ordered optionally). It is also pos-
sible to connect an external automatic reclosure and/or synchronism check as well as
double protection with one or two automatic reclosure functions.
®
4 7SA522 is a selective and quick protec-
7SA522 Manual
C53000-G1176-C155-3