Siemens SIPROTEC 7UT613 series Manual page 111

Fault Detection,
Dropout
7UT613/63x Manual
C53000-G1176-C160-2
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 I and I
diff stab
tection. If the quantities result in an operating point which lies in the trip area, a trip
signal is given. If the current conditions I
(≥ 9 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 detection.
Normally, a differential protection does not need a „pickup", since the condition for a
fault detection is identical to the trip condition. Like all SIPROTEC 4 devices, however,
the differential protection feature of the 7UT613/63x 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 func-
tions 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.
Figure 2-24 Pickup of the Differential Protection
If restraint by higher-order harmonics is activated, the system first performs a harmon-
ic analysis (approx. 1 cycle) to check the restraint conditions as the case may be. Oth-
erwise, tripping occurs as soon as the tripping conditions are fulfilled.
For special cases, the trip command can be delayed. The following logic diagram il-
lustrates the tripping logic.
are assigned to the trip characteristic by the differential pro-
/I
diff stab
2.2 Differential Protection
appear near the fault characteristic
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