Introduction
1.2 Application Scope
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
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1.2
Application Scope
The digital Line Differential Protection SIPROTEC 4 7SD80 is a selective short-circuit protection for overhead
lines and cables with single- and multi-ended infeeds in radial, ring or any type of meshed systems of any trans-
mission level. The measured data are compared separately for each phase.
A major advantage of the differential protection principle is the instantaneous tripping in the event of a short
circuit at any point within the entire protected zone. The current transformers limit the protected zone at the
ends towards the remaining system. This rigid delimitation is the reason why the differential protection scheme
shows such an ideal selectivity.
The differential protection system requires a 7SD80 device as well as a set of current transformers at either
end of the protected zone. Voltage transformers are not required for the differential protection functions in the
7SD80; they are, however, available to record and display measured values (voltages, power, power factor) or
when using a directional overcurrent protection element.
The devices located at the ends of the protected zone exchange measuring information via protection interfac-
es using communication links (usually optical fiber or copper cables).
Since fault-free data transmission is the prerequisite for the proper operation of the protection, it is continuously
monitored internally.
Protection Functions
The device's basic function is to detect short-circuits or ground faults in the protected zone – even weak-current
or high-resistance short-circuits. Even complex multiphase faults are detected correctly, as the measured
values are evaluated separately for each phase. The protection is restraint against inrush currents of power
transformers. When switching a line onto a fault, it is possible to send an instantaneous trip signal. The 7SD80
line differential protection includes the differential protection functions of phase comparison protection and
ground fault differential protection. Both differential protection functions operate independently of each other.
In the event of a communication failure, the devices can automatically switch to emergency operation using an
integrated overcurrent protection until communication is restored. The overcurrent protection comprises two
definite time-overcurrent protection elements and one inverse time-overcurrent protection element. Both ele-
ments operate directional or non-directional. Additionally, the device features a third definite time-overcurrent
protection element that always operates non-directionally.
For inverse time overcurrent protection, several characteristic curves of different standards are available.
Alternatively, the time overcurrent protection can be used as a backup time overcurrent protection, i.e. it oper-
ates independent of and parallel to the differential protection at either end.
The communication link can be used for transmitting further information. Besides measured values, it is possi-
ble to transmit binary information.
All protection functions in the 7SD80 always trip 3-pole. They can work together with an integrated automatic
reclose function (optional). The automatic reclose functions enables 3-pole automatic reclosing with two
reclose attempts.
The thermal overload protection protects cables and power transformers from inadmissible heating due to over-
load.
Additionally, a two-element overvoltage and undervoltage protection and a four-element frequency protection
can be used. A circuit-breaker failure protection monitors the response of the circuit breaker following a trip
command.
