Setting Of The Parameters For This Function; Fault Detection; Overcurrent Fault Detection - Siemens siprotec 7SA6 User Manual

6.2.1.2

Setting of the Parameters for this Function

6.2.2

Fault detection

6.2.2.1

Overcurrent Fault Detection

7SA6 Manual
C53000-G1176-C133-1
In systems with earthed star-point, the setting ,! 7KUHVKROG (Address ) is
set somewhat below the minimum expected earth short-circuit current. 3I
as the sum of the phase currents |I
of the set of current transformers. In non-earthed systems the setting value is
somewhat below the earth current value for double earth faults.
With regard to the setting 8! 7KUHVKROG (Address ), in systems with earthed
starpoint, care must be taken that operational unsymmetries do not cause a pick-up.
3U is defined as the sum of the phase-earth voltages |U
0
–criterion should be ignored, the address  is set to ∞. In non-earthed systems
U
0
this setting is not relevant and therefore not accessible.
The preset value ,!,SKPD[ =  (Address ) usually is sufficient for the
slope of ,–characteristic ,! ,SKPD[ (Address ). This setting can only be
®
changed with DIGSI 4 under "Additional Settings".
These settings are listed in a table in Subsection 6.2.2.4.
Fault detection has to detect a faulty condition in the power system and to initiate all
the necessary procedures for selective clearance of the fault:
• Start the delay times for the directional and non-directional final stages
• Determination of the faulted loops
• Release of impedance calculation and direction determination
• Release of tripping command
• Initiation of supplementary functions
• Indication/output of the faulty phase(s)
Depending on the ordered version, the 7SA6 distance protection has a range of fault
detection modes, from which the appropriate type for the particular system conditions
can be selected. If, according to the ordering code, the device only has impedance
fault detection, or if you set ',6 3,&.83 = = TXDGULODW (address ) as
detection mode, this Section 6.2.2 is of no importance. This type of fault detection
works implicitly, i.e the above-mentioned operations are executed automatically as
soon as a fault is detected in one of the distance zones.
Overcurrent pick-up is a per phase fault detection mode. After numerical filtering, the
currents are monitored to check if they exceed the set values in every phase. An
output signal is given for the phase(s) where the set threshold is exceeded.
For the processing of the measured values (see Section 6.2.3) the per phase pick-up
signals are converted into loop information. This is done subject to earth-fault
detection according to Section 6.2.1 and — in the earthed network — subject to the
+ I + I |, which equals the star-point current
L1 L2 L3
L1–E
Functions
is defined
0
+ U + U |. If the
L2–E L3–E
6-31