Applications - Siemens siprotec 7SA522 User Manual

Introduction
1.2

Applications

Protection
Functions
1-4
The numerical Distance Protection SIPROTEC
tection device for overhead lines and cables with single- and multi-ended infeeds in
radial, ring or any type of meshed systems with an earthed system star-point.
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 volt-
age levels.
Recognition of the distance to fault with distance protection measurement, is the basic
function of the device. In particular for complex multiphase faults, the distance protec-
tion has a non-switched 6-impedance-loops design (fullscheme). The influence of
wrong distance measurement due to parallel lines can be compensated by feeding the
earth current of the parallel line to the relay. Parallel line compensation can be used
for distance protection as well as for the fault locator. It may be supplemented by tel-
eprotection 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 a directional comparison scheme. 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 scheme. Subsequent 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 sig-
nal.
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 time delayed overcurrent protec-
tion, until the measured voltage again becomes available. The overcurrent protection
consists of three definite time overcurrent stages and an inverse time (IDMT) stage.
For the IDMT stage, a number of characteristics based on various standards are avail-
able. Alternatively, the time delayed overcurrent protection may be used as back-up
time delayed overcurrent protection, i.e. it functions independant and in parallel to the
distance protection.
Depending on the version ordered, the short-circuit protection may also trip single-
pole. It may work in co-operation with an integrated automatic reclosure (available as
an option) with which single-pole, three-pole or single and three-pole automatic reclos-
ure as well as several interrupt cycles are possible on overhead lines. Before reclos-
ure after three-pole tripping, the permissibility of the reclosure can be checked by volt-
age and/or synchronization check by the device. It is possible to connect an external
automatic reclosure and/or synchronization device as well as double protection with
one or two automatic reclosure functions.
Apart from the short-circuit protection functions mentioned, further protection func-
tions are possible such as overvoltage protection, circuit breaker failure protection and
protection against the effects of power swings (simultaneously active as power swing
blocking for the distance protection). For the rapid location of the damage to the line
after a short-circuit, a fault locator is integrated which also may compensate for the in-
fluence of a parallel line and load.
®
7SA522 is a fast and selective pro-
C53000-G1176-C119-2
7SA522 Manual