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The corresponding time multiplier for an IEC Curve is set at address 1208 51 TIME DIAL and in address
1209 51 TIME DIAL for an ANSI Curve. It must be coordinated with the time coordination chart of the system.
The time multiplier can also be set to ∞. In this case, the Element will not trip after pickup. However, pickup will
be signaled. If the 51 Element is not required at all, address 112 Charac. Phase should be set to Definite
Time during protection function configuration (see Section 2.1.1.2).
If highly sensitive settings close to the load current are required in weak power systems or transformers, the
element can be stabilized via the undervoltage as an additional criterion for the power system fault. The oper-
ating modes can be set in address 1223 VOLT. INFLUENCE. In a voltage-controlled operation, the voltage
threshold is defined via parameter 1224 51V V< below which the current element is released.
51N Element (Ground) with IEC or ANSI Characteristics
Having set address 113 Charac. Ground = TOC IEC when configuring the protection functions (Section
2.1.1), the parameters for the inverse time characteristics will also be available. Specify in address 1311 51N
IEC CURVE the desired IEC Curve (Normal Inverse, Very Inverse, Extremely Inv. or Long
Inverse). If address 113 Charac. Ground was set to TOC ANSI, you can select the desired ANSI Curve
(Very Inverse, Inverse, Short Inverse, Long Inverse, Moderately Inv., Extremely Inv. or
Definite Inv.) in address 1312 51N ANSI CURVE.
If the inverse time trip characteristic is selected, it must be noted that a safety factor of about 1.1 has already
been included between the pickup value and the setting value. This means that a pickup will only occur if a
current of about 1.1 times the setting value is present. If Disk Emulation was selected at address 1310 51
Drop-out, reset will occur in accordance with the reset curve as described before.
The current value is set in address 1307 51N PICKUP. The setting is mainly determined by the minimum an-
ticipated ground fault current.
The corresponding time multiplier for an IEC Curve is set at address 1308 51N TIME DIAL and at address
1309 51N TIME DIAL for an ANSI Curve. This has to be coordinated with the grading coordination chart of
the network. For ground currents with grounded network, you can often set up a separate grading coordination
chart with shorter delay times.
The time multiplier can also be set to ∞. In this case, the Element will not trip after pickup. However, pickup will
be signaled. If the 51N-TOC Element is not required at all, address 113 Charac. Ground should be set to
Definite Time during configuration of the protection functions (see Section 2.1.1).
Inrush Restraint
When applying the protection device to transformers where high inrush currents are to be expected, the 7SK80
can make use of an inrush restraint function for the overcurrent elements 50-1, 51, 50N-1 and 51N.
Inrush restraint is only effective and accessible if address 122 InrushRestraint was set to Enabled. If this
function is not required, then Disabled is set. In address 2201 INRUSH REST., the function is switched ON
or OFF jointly for the overcurrent elements 50-1 PICKUP, 51 PICKUP, 50N-1 PICKUP, and 51N PICKUP
The inrush restraint is based on the evaluation of the 2nd harmonic present in the inrush current. Upon delivery
from the factory, a ratio I
changed. The setting value is identical for all phases and Ground. However, the component required for re-
straint may be adjusted to system conditions in address 2202 2nd HARMONIC. To provide more restraint in
exceptional cases, where energizing conditions are particularly unfavorable, a smaller value can be set in the
aforementioned address, e.g. 12 %. Irrespective of parameter 2202 2nd HARMONIC, rush blocking will only
occur if the absolute value of the 2nd harmonic is at least 0.125 * I
The effective duration of the cross-blocking 2203 CROSS BLK TIMER can be set to a value between 0 s (har-
monic restraint active for each phase individually) and a maximum of 180 s (harmonic restraint of a phase
blocks also the other phases for the specified duration).
If the current exceeds the value set in address 2205 I Max, no further restraint will take place for the 2nd har-
monic.
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
/I
of 15 % is set. Under normal circumstances, this setting will not need to be
2f
f
2.2 Overcurrent Protection 50, 51, 50N, 51N
.
Nom,sec
Functions
81
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