Set pickup values refer to symmetrical three-phase currents for three-phase protected objects. For singlephase
transformers the currents are presumed at phase opposition. With single-phase busbar protection the summa-
tion transformers are to be considered, if applicable. The rated currents of the measured current inputs are
important, if the device is connected via a summation transformer is generally 0.1 A.
When testing with the operational parameters, it should be noted that the setting value for the differential
protection refers to the rated current of the transformer, i.e. to the primary current which results from
[dreiphasenobjekt-inobj, 1, en_GB]
in 3-phase object and
[einphasenobjekt-inobj, 1, en_GB]
for 1-phase object with
S
N Obj
Rated apparent power of the protective object
U
N Obj
Rated voltage of the protected object or protected transformer winding.
For a winding with parameterised voltage according to Section 2.1.5 Setting Groups calculated voltage is
valid.
For transformers the actual pickup values for single or two-phase tests depend on the vector group of the
transformer; single-phase tests also depend on the starpoint condition and current processing. This corre-
sponds to conventional circuitry when current is fed in via matching transformers.
To obtain the actual pickup value, the set value has to be multiplied with the vector group factor kVG and the
following equation:
[faktor-ksg-3phasentr, 1, en_GB]
The following table shows these changes as a factor k
VG
depending on the vector group and the type of fault,
for three-phase transformers.
Table 3-31
Correction Factor k
VG
depending on vector group and fault type
Type of Fault Reference Winding
(high voltage)
even VG numeral
(0, 2, 4, 6, 8, 10)
uneven VG numeral
(1, 3, 5, 7, 9, 11)
3-phase 1 1 1
2-phase 1 1 √3/2 ≈ 0,866
1-phase
with Ι
0
-elimination
3/2 = 1,5 3/2 = 1,5 √3 ≈ 1,73
1-phase
without Ι
0
-elimina-
tion
1 1
Example:
3-phase transformer
S
N
= 57 MVA
Vector Group Yd5
Rated voltage (high-voltage winding) U
Nom
= 110 kV
Current Transformer 300 A/1 A
Mounting and Commissioning
3.3 Commissioning
366 SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
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