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The following table shows this factor k
SG
in dependence of the vector group and the fault type.
Table 11-2 Correction Factor k
SG
for the Vector Group (SG) and Fault Type
Fault Type Reference Winding
(High Voltage)
Even SG Number
(0, 2, 4, 6, 8, 10)
Odd SG Number (1, 3,
5, 7, 9, 11)
3-phase 1 1 1
2-phase 1 1 √3/2 ≈ 0.866
1-phase with I
0
elimination 3/2 = 1.5 3/2 = 1.5 √3 ≈ 1.73
1-phase without I
0
elimination 1 1 3/(1+√3) ≈ 1.1
Primary Tests
Restricted primary testing is possible for capacitor-bank applications. A wiring fault in the connection to the
system could be a possible cause of the fault. With the system at a standstill, you can apply a test current of
approx. 10 % to 20 % of the rated current directly to the transformer terminals and connected transformer
with a primary testing device. Simulate a load (through-flowing current). The differential current must be 0
and the restraint current is the current which is fed in.
To rule out overfunction on initial switch-on, for example, due to the incorrect installation of a transformer,
Siemens recommends switching the differential protection to test mode. The protection function operates,
but does not issue a trip command. With the protection measurement values in the fault log, check the differ-
ential and the restraint current. The differential current must be 0 and the restraint current must correspond
to the actual capacitor current.
If the differential protection is functioning correctly, switch the protection function ON.
NOTE
If the differential protection is disabled (for example, function in test mode), an overcurrent protection
must be active as short-circuit protection (without delay and set via the starting current).
11.17.2
Functional Tests
11.17 Functional Test Differential Protection for Capacitor Banks
SIPROTEC 5, Overcurrent Protection, Manual 1403
C53000-G5040-C017-8, Edition 07.2017
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