Specifications

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Overcurrent Protection SIPROTEC 7SJ81

5/6 SIPROTEC Compact · SIEMENS SIP 3.01 · Edition 3

for Low-Power CT and VT Applications – Application sheets

Protection functions

Overcurrent protection (ANSI 50, 50N, 51, 51N)

This function is based on the phase-selective measurement

of the three phase currents and the ground current (four

transformers). Three deﬁ nite time-overcurrent protection

elements (DMT) are available both for the phase and the

ground elements. The current threshold and the delay time

can be set in a wide range.

Inverse time-overcurrent protection characteristics (IDMTL)

can also be selected and activated.

Reset characteristics

Time coordination with electromechanical relays is made

easy with the inclusion of the reset characteristics according

to ANSI C37.112 and IEC 60255-3/BS 142 standards. When

using the reset characteristic (disk emulation), the reset pro-

cess is initiated after the fault current has disappeared. This

reset process corresponds to the reverse movement of the

Ferraris disk of an electromechanical relay (disk emulation).

Available inverse-time characteristics

Characteristics acc. to IEC 60255-3 ANSI/IEEE

Inverse



Short inverse



Long inverse



Moderately inverse



Very inverse



Extremely inverse



Table 5/2 Available inverse-time characteristics

Inrush restraint

If second harmonic content is detected during the energi-

zation of a transformer, the pickup of stages I >, I

, I >

dir

and I

dir

is blocked.

Dynamic settings group switching

In addition to the static parameter changeover, the pickup

thresholds and the tripping times for the directional and

non-directional time-overcurrent protection functions can

be changed over dynamically. As changeover criterion, the

circuit-breaker position, the prepared auto-reclosure, or a

binary input can be selected.

Directional comparison protection (cross-coupling)

It is used for selective instantaneous tripping of sections

fed from two sources, i.e. without the disadvantage of time

delays of the set characteristic. The directional comparison

protection is suitable if the distances between the protection

zones are not signiﬁ cant and pilot wires are available for

signal transmission. In addition to the directional comparison

protection, the directional coordinated time-overcurrent

protection is used for complete selective backup protection.

Directional time-overcurrent protection (ANSI 67, 67N)

Directional phase and ground protection are separate func-

tions. They operate in parallel to the non-directional overcur-

rent elements. Their pickup values and delay times can be set

separately. Deﬁ nite-time and inverse-time characteristics are

offered. The tripping characteristic can be rotated by ± 180

degrees.

By making use of the voltage memory, the directionality can

be determined reliably even for close-in (local) faults. If the

primary switching device closes onto a fault and the voltage

is too low to determine direction, the direction is determined

using voltage from the memorized voltage. If no voltages are

stored in the memory, tripping will be according to the set

characteristic.

For ground protection, users can choose whether the direc-

tion is to be calculated using the zero-sequence or negative-

sequence system quantities (selectable). If the zero-sequence

voltage tends to be very low due to the zero-sequence impe-

dance it will be better to use the negative-sequence quantities.

Fig. 5/4 Directional characteristics of the directional

time-overcurrent protection

(Sensitive) directional ground-fault detection

(ANSI 59N/64, 67Ns, 67N)

For isolated-neutral and compensated networks, the direc-

tion of power ﬂ ow in the zero sequence is calculated from

the zero-sequence current I

and zero-sequence voltage V

For networks with an isolated neutral, the reactive current

component is evaluated; for compensated networks, the

active current component or residual resistive current is eva-

luated. For special network conditions, e.g. high-resistance

grounded networks with ohmic-capacitive ground-fault

current or low-resistance grounded networks with ohmic-

inductive current, the tripping characteristics can be rotated

approximately ± 45 degrees (see Fig.5/5).

Two modes of ground-fault direction detection can be

implemented: tripping or “signalling only mode”.