Inverse Time Overcurrent Protection - Siemens SIPROTEC 4 7UT6 Series Manual

[logikdia-ueberstromstufe-ie-fuer-erdstrom-121102-st, 1, en_GB]
Figure 2-81

Inverse Time Overcurrent Protection

2.5.3
The inverse time overcurrent stage operates with a characteristic either according to the IEC- or the ANSIstan-
dard or to a user-defined characteristic. The characteristics and their equations are given in the "Technical
Data". When configuring one of the inverse time characteristics, definite time stages IE>> and IE> are also
enabled.
Pickup, Trip
The current measured at the assigned 1-phase current input is compared with setting value IEp. If the current
exceeds 1.1 times the set value, the stage picks up and an annunciation is made. If inrush restraint is used, a
frequency analysis is performed first. If an inrush condition is detected, pickup annunciation is suppressed and
an inrush message is output instead. The RMS value of the fundamental is used for the pickup. During the
pickup of an I
Ep
measuring procedure, depending on the selected tripping characteristic. After expiration of this time period, a
trip command is output as long as no inrush current is detected or inrush restraint is disabled. If inrush
restraint is enabled and inrush current is detected, there will be no tripping. Nevertheless, an annunciation is
generated indicating that the time expired.
The following figure shows the logic diagram of the inverse-time overcurrent protection function.
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
Logic diagram of the overcurrent stage IE> for earth current (simplified)
stage, the tripping time is calculated from the flowing fault current by means of an integrating
2.5 Time Overcurrent Protection for Earth Current
Functions
163