Mounting and Commissioning
3.2 Checking Connections
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
395
In order to obtain the pickup value, the setting value I-DIFF> (parameter address 2021) must be multiplied
by the factor
Table 3-27 Correction factor k
VG
depending on vector group and fault type
The pickup values are checked for each winding by slowly increasing the test current with the secondary test
set. Tripping is initiated when the converted pickup value is reached.
Example (Application as „mere transformer protection“):
Three-phase transformer S
N Transf
= 57 MVA, vector group Yd5
High Voltage 110 kV
Current Transformer 300 A / 1 A
Undervoltage 25 kV
Current Transformer 1500 A / 1 A
The following applies for the high voltage winding:
In this case the rated current of the winding is practically equal to the current transformer rated current. Thus,
the pickup value (referred to the rated relay current) complies with the setting value I DIFF> of the relay when
three or two-phase testing is performed (k
VG
= 1 for reference winding). For single-phase testing with zero se-
quence current elimination, a pickup value 1.5 times higher must be expected.
The following applies for the secondary winding:
When testing this winding, the pickup value (referred to the rated device current) will amount to
Type of Fault Reference winding
(High Voltage)
Even VG Numeral
(0, 2, 4, 6, 8, 10)
Odd VG Numeral
(1, 3, 5, 7, 9, 11)
Three-phase 1 1 1
Two-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
elimina-
tion
11√3 = 1.73
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