3.3 Commissioning
391
7UT613/63x Manual
C53000-G1176-C160-2
To obtain the actual pickup value, the set value has to be multiplied with the vector
group factor k
VG
and the following equation:
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 3-26 Correction Factor k
VG
depending on vector group and fault type
Example:
three-phase transformer S
N
=57MVA
Vector Group Yd5
Rated voltage
(high-voltage winding) U
N
=110kV
Current Transformer 300 A/1 A
Rated voltage
(high-voltage winding) U
N
=25kV
Current Transformer 1500 A / 1 A
The following applies to the high voltage winding:
In this case the rated current of the winding is practically equal to the current trans-
former rated current. Thus, the pickup value (referred to the rated relay current) com-
plies with the setting value I-DIFF> of the device (k
VG
= 1 for reference winding). For
single-phase testing with zero sequence current elimination, a pickup value 1.5 times
higher must be expected.
The following applies to the low voltage winding:
When testing this winding, the pickup value (referred to the rated device current) will
amount to
Because of the odd vector group numeral, the following pickup values apply (Table )
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
single-phase
with I
0
elimination
3/2 = 1,5 3/2 = 1,5 √3 ≈ 1,73
single-phase
without I
0
elimination
11
To Next Page
Loading...
