1.2 Application Scope
19
7SD610 Manual
C53000-G1176-C145-4
1.2 Application Scope
The numerical 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 transmission 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 transformer 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 re-
quired. However, they are available for indicating and processing of measured values
(voltages, power, power factor), or when using a directional overcurrent protection
stage (ordering variant).
The devices located at the ends of the protected zone exchange measuring informa-
tion via protection data interfaces 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-connected power
transformer (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 segregat-
ed. The protection system is restrained against inrush currents of power transformers.
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 signal.
In the event of a communication failure, the devices can automatically be switched to
emergency operation using an integrated time overcurrent protection until communi-
cation is restored again. This overcurrent protection has three current-independent
stages and one current-dependent stage. Furthermore, the device has a directional
current-independent stage and a directional current-independent stage which enables
an increased selectivity of the emergency function. For inverse time overcurrent pro-
tection stages, several curves of different standards are provided.
Alternatively, the time overcurrent protection can be used as a backup time overcur-
rent protection, i.e. it operates 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 operate in co-operation with an integrated automatic reclosure
(optionally). The automatic reclose function may be used on overhead lines for single-
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