Siemens SIPROTEC 4 7UT6 Series Manual page 98

Functions
2.2 Differential Protection
[diff-ausloesekennl-mitinfos-020926-rei, 1, en_GB]
Figure 2-23
Differential currents above branch d cause immediate trip regardless of the restraining quantity and harmonic
content (setting I-DIFF>>). This is the operating range of the "Fast Unrestrained Trip with High-current
Faults".
The area of add-on restraint is the operational area of the saturation indicator (see margin heading "Add-on
Restraint during External Faults").
The values Ι and Ι
diff
result in an operating point which lies in the trip area, a trip signal is given. If the current conditions Ι
appear near the fault characteristic (≥ 80 % of the slope of the fault characteristic), tripping occurs even when
the trip characteristic has been excessively increased due to add-on stabilisation, startup or DC current detec-
tion.
Fault Detection, Dropout
Normally, a differential protection does not need a "pickup", since the condition for a fault detection is iden-
tical to the trip condition. Like all SIPROTEC 4 devices, however, the differential protection feature of the
7UT6x has a pickup that is the starting point for a number of subsequent activities. The pickup marks the
beginning of a fault. This is necessary e.g. for creating fault logs and fault records. However, internal functions
also require the instant of fault inception even in case of an external fault, e.g. the saturation indicator which
has to operate correctly in case of an external fault.
As soon as the fundamental wave of the differential current exceeds approximately 85 % of the set value or
the restraining current reaches 85 % of the add-on restraint area, the protection picks up. A pickup signal is
also issued when the high-speed trip stage for high-current faults picks up.
98
Tripping characteristic of the differential protection
are assigned to the trip characteristic by the differential protection. If the quantities
stab
diff
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
/Ι
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