Specifications

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Line Differential Protection SIPROTEC 7SD80

3/6 SIPROTEC Compact · SIEMENS SIP 3.01 · Edition 3

Application sheets

Protection functions

Differential protection (ANSI 87L, 87N L, 87Ns L)

The differential protection SIPROTEC 7SD80 consists of two

separately operating differential protection algorithms:

• Phase comparison protection (PCP)

• Earth-fault differential protection (EFD).

The phase comparison protection, PCP, offers a safe and

robust short-circuit protection for all types of neutral treat-

ment. Of course, this is also valid for application in systems

with isolated or resonant-earthed neutral. Adaptation of

the phase comparison protection according to the neutral

treatment is done by setting parameters via DIGSI.

The earth-fault differential protection, EFD, operates with

two different algorithms, depending on the neutral treat-

ment in the power system to be protected.

For application in solidly, low-resistance or high-resistance

earthed systems, the EFD analyzes the measured zero-se-

quence current. The fundamental wave of the zero-sequence

current is determined by ﬁ ltering. The ﬁ ltered zero-sequence

currents of the local side and the opposite side are added

and provide the zero-sequence differential current. The ad-

aptive stabilizing facilitates the parameterization and assured

stability and selectivity.

For application in power systems with isolated or resonant-

earthed neutrals, the connection of voltages – at least of the

zero-sequence voltage – and the use of a sensitive earth-cur-

rent transformer is required. From the zero-sequence current

and the voltage, the apparent power of the zero-sequence

system is calculated, and compared with the opposite end.

Depending on the direction of the power ﬂ ow, an internal or

external earth fault is detected. This is only indicated, and

can be shut down immediately or with a set delay.

Circuit-breaker intertripping (ANSI 85 DT)

The 7SD80 devices have an integrated circuit-breaker inter-

tripping function for tripping the circuit-breaker at the oppo-

site end. The circuit-breaker intertripping can be activated

directly by the differential protection functions, but also

through binary signals of any other external or internal pro-

tection function. The circuit-breaker intertripping can be

combined with an integrated phase and/or zero-sequence

current threshold, which permits to trip the circuit-breaker

if there is a sufﬁ ciently high current.

Overcurrent protection, non-directional/directional

(ANSI 50, 50N, 51, 51N, 67, 67N)

This function is based on the phase-selective measurement

of the three phase currents and the earth current (4 instru-

ment transformers).

In the SIPROTEC 7SD80, three deﬁ nite time-overcurrent

protection stages are integrated for protection against phase

faults, as well as for protection against earth faults. The current

threshold and the delay time can be set for each stage. Fur-

thermore, inverse time-overcurrent protection characteristics

can be added.

Each of the overcurrent protection stages can be set as emer-

gency or backup protection independently of each other. This

enables the integration of the SIPROTEC 7SD80 in a simple

busbar protection concept by means of reverse interlocking.

When voltage transformers are connected, a directional

time-overcurrent protection emergency function can be

activated if the protection interface communication fails.

Available inverse-time characteristics

Characteristics acc. to IEC 60255-3 ANSI/IEEE

Inverse



Short inverse



Long inverse



Moderately inverse



Very inverse



Extremely inverse



Tabelle 3/2 Available inverse-time characteristics

Inrush restraint

When the second harmonic is detected while energizing a

transformer inside or outside of the protection zone, pickup

of the differential protection stages or the overcurrent

protection stages can be suppressed.

Breaker failure protection (ANSI 50BF)

If a faulted portion of the electrical circuit is not disconnected

when a trip command is issued to a circuit-breaker, another

trip command can be initiated using the breaker failure protec-

tion which trips the circuit-breaker of an upstream feeder.

Breaker failure is detected if, after a trip command is issued

the current keeps on ﬂ owing into the faulted circuit. It is also

possible to make use of the circuit-breaker position contacts

for indication as opposed to the current ﬂ owing through the

circuit-breaker.

External trip initiation

Through a binary input, an external protection device or mo-

nitoring equipment can be coupled into the signal processing

of the SIPROTEC 7SD80 to trip the local circuit-breaker.