Siemens 7SK80 Manual page 80

Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
50-1 Element (phases)
For setting the 50-1 element, it is the maximum anticipated load current that must be considered above all.
Pickup due to overload should never occur since in this mode the device operates as fault protection with cor-
respondingly short tripping times and not as overload protection. For this reason, a setting equal to 20% of the
expected peak load is recommended for line protection, and a setting equal to 40% is recommended for trans-
formers and motors.
The settable time delay (address 1205 50-1 DELAY) results from the grading coordination chart defined for
the system.
The selected time is an additional delay time and does not include the operating time (measuring time, dropout
time). The delay can also be set to ∞. In this case, the Element will not trip after pickup. However, pickup, will
be signaled. If the 50-1 Element is not required at all, then the pickup threshold 50-1 should be set to ∞. This
setting prevents tripping and the generation of a pickup message.
50N-1 Element (Ground)
The 50N-1 element is normally set based on minimum ground fault current.
If the relay is used to protect transformers or motors with large inrush currents, the inrush restraint feature of
7SK80 may be used for the 50N–1 relay element. It can be enabled or disabled for both the phase current and
the ground current in address 2201 INRUSH REST.. The characteristic values of the inrush restraint are listed
in Subsection "Inrush Restraint".
The settable delay time (address 1305 50N-1 DELAY) results from the time coordination chart defined for the
system. For ground currents in a grounded system a separate coordination timer with short time delays can be
applied.
The selected time is an additional delay time and does not include the operating time (measuring time, dropout
time). The delay can also be set to ∞. In this case, the Element will not trip after pickup. However, pickup, will
be signaled. If the 50N-1 Element is not required at all, the pickup threshold 50N-1 PICKUP should be set to
∞. This setting prevents tripping and the generation of a pickup message.
Pickup Stabilization (Definite Time)
The configurable dropout times 1215 50 T DROP-OUT or 1315 50N T DROP-OUT can be set to implement
a uniform dropout behavior when using electromechanical relays. This is necessary for a time grading. The
dropout time of the electromechanical relay must be known to this end. Subtract the dropout time of the device
(see Technical Data) from this value and enter the result in the parameters.
51 Element (phases) with IEC or ANSI characteristics
Having set address 112 Charac. Phase = TOC IEC or TOC ANSI when configuring the protection functions
(Section 2.1.1.2), the parameters for the inverse time characteristics will also be available.
If address 112 Charac. Phase was set to TOC IEC, you can select the desired IEC Curve (Normal
Inverse, Very Inverse, Extremely Inv. or Long Inverse) at address 1211 51 IEC CURVE. If
address 112 Charac. Phase 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.)
at address 1212 51 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 1210 51
Drop-out, reset will occur in accordance with the reset curve as described before.
The current value is set in address 1207 51 PICKUP. The setting is mainly determined by the maximum an-
ticipated operating current. Pickup due to overload should never occur since in this mode, the device operates
as fault protection with correspondingly short tripping times and not as overload protection.
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SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012