Application Scope - Siemens SIPROTEC 7SD610 Manual

1.2

Application Scope

The digital Differential Protection SIPROTEC 4 7SD610 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 voltage
level. Conditioning of the system starpoint is irrelevant, as measuring data are compared separately for each
phase.
High sensitivity and the inrush current restraint allow for the application of the 7SD610 even if a power trans-
former is located within the protected zone (ordering option) whose starpoint(s) might also be isolated, earthed
or provided with a Petersen coil.
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 7SD610 device as well as a set of current transformers at either
end of the protected zone. Voltage transformers are not required. However, they are available for indicating and
processing of measured values (voltages, power, power factor), or when using a directional overcurrent pro-
tection stage (ordering variant).
The devices located at the ends of the protected zone exchange measuring information via protection data in-
terfaces using dedicated communication links (usually fibre-optic cables) or a communication network. Using
7SD610, a protected object with two ends can be protected: cable, overhead line or both, even with unit-con-
nected power transformer (ordering option). For each end, a 7SD610 is used.
Since fault-free data transmission is the prerequisite for the proper operation of the protection, it is continuously
monitored internally.
Protection Functions
Recognition of short-circuits in the protection zone – even of weak-current or high-resistive shorting – is the
basic function of the device. Even complex multiphase faults are precisely detected, as the measured values
are evaluated phase-segregated. The protection system is restrained against inrush currents of power trans-
formers. When switching onto a fault at any point of a line, an undelayed trip signal can be emitted.
In the event of a communication failure, the devices can automatically be switched to emergency operation
using an integrated time overcurrent protection until communication is restored. This overcurrent time protec-
tion has three definite-time overcurrent stages and one inverse-time stage. Furthermore, the device has one
directional definite-time overcurrent stage and one directional inverse stage which enables an increased selec-
tivity of the emergency function. For inverse time overcurrent protection stages, several curves of different stan-
dards are provided.
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 connection can be used for transmitting further information. Besides measured values,
binary commands or other information can be transmitted as well (ordering variant).
Depending on the order variant, the short-circuit protection functions may also trip single-pole, and may work
in co-operation with an integrated automatic reclosure (optionally). The automatic reclosure function enables
for single-pole, three-pole or single- and three-pole automatic reclosure as well as several interrupt cycles on
overhead lines.
Apart from the short-circuit protection functions mentioned, a thermal overload protection has been integrated
which protects in particular cables and power transformers from undue heating through overload. Furthermore,
multi-step over- and undervoltage as well as frequency protection and restricted earth fault protection can be
used (ordering variant). An optional circuit breaker failure protection monitors the circuit breaker response after
a trip command (ordering variant).
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
Introduction
1.2 Application Scope
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