3.2 Checking Connections and System (Plant) Integration
341
7UM62 Manual
C53000-G1176-C149-3
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
= 57 MVA, vector group Yd5
Primary (higher) voltage 110 kV
Current transformers
300 A/1 A
Secondary (lower) voltage25 kV
Current transformers
1500 A/1 A
The following applies for the primary 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 set IDIFF> of the relay when three or two-phase testing is performed
(k
VG
= 1 for reference winding). With single-phase testing and zero sequence current
elimination, a pickup value 1.5 times higher must be expected.
The following applies for the secondary winding:
Table 3-23
Correction Factor k
VG
Depending on Vector Group and Fault Type
Type of Fault
Reference Winding
(High Voltage Side)
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
elimination
1
1
√
3 = 1.73
I
N Transf
S
N Transf
MVA
]
[
1000
⋅
3 U
⋅
N Winding
kV
]
[
------------------------------------------------------------
=
[A]
57 MVA
]
[
1000
⋅
3 110
⋅
(
)
kV
]
[
--------------------------------------------
=
[A] = 299.2 A
I
N Transf
S
N Transf
MVA
]
[
1000
⋅
3 U
⋅
N Winding
kV
]
[
------------------------------------------------------------
=
[A]
57 MVA
]
[
1000
⋅
3 25
⋅
(
)
kV
]
[
--------------------------------------------
=
= 1316 A
[A]
