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 Defi-
nite Time during protection function configuration (see Section 2.1.1.2 Setting Notes).
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 Functional Scope), the parameters for the inverse time characteristics will also be available. Specify in
address 113 Charac. Ground = TOC IEC the desired IEC characteristic (Normal Inverse, Very
Inverse, Extremely Inv. or Long Inverse). If address 113 Charac. Ground = TOC ANSI, you can
select the desired ANSI characteristic (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
anticipated ground fault current.
The corresponding time multiplier for an IEC characteristic is set at address 1308 51N TIME DIAL and at
address 1309 51N TIME DIAL for an ANSI characteristic. This has to be coordinated with the grading coordi-
nation 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 elementt 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 Functional Scope).
Inrush Restraint
When applying the protection device to transformers where high inrush currents are to be expected, the
7SJ80 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 Ι2f/Ιf of 15 % is set. Under normal circumstances, this setting will not need to
be changed. The setting value is identical for all phases and ground. However, the component required for
restraint 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 * INom,sec.
The effective duration of the cross-blocking 2203 CROSS BLK TIMER can be set to a value between 0 s
(harmonic 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
harmonic.
Manual Close Mode (phases ground)
When a circuit breaker is closed onto a faulted line, a high-speed trip by the circuit breaker is usually desired.
For overcurrent or high-set element the delay may be bypassed via a Manual Close pulse, thus resulting in
instantaneous tripping. The internal "Manual close" signal is built from the binary input signal >Manual Close
(no.
356
). The internal "Manual close" signal remains active as long as the binary input signal >Manual Close is
active, but at least for 300 ms (see the following logic diagram). To enable the device to react properly on
Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
SIPROTEC 4, 7SJ80, Manual 75
E50417-G1140-C343-A8, Edition 12.2017