2 Functions
98
7UM61 Manual
C53000-G1176-C127-3
The following formula is generally valid for the primary impedance (with limiting to the
unit transformer):
with
k
R
Protection zone reach [%]
u
K
Relative transformer short-circuit voltage [%]
S
N
Rated transformer power [MVA]
U
N
Machine-side rated transformer voltage [kV]
The derived primary impedances must be converted for the secondary side of the
current and voltage transformers. In general:
The nominal current of the protection device (= secondary nominal current of the
current transformer) is automatically considered by the device. You have already com-
municated the transformation ratios of the current and voltage transformers to the
device by entering the nominal transformer values (see section 2.3).
Example:
Transformer data:
u
K
= 7 %
S
N
= 5.3 MVA
U
N
= 6.3 kV
Transformation ratios:
Current transformer ratio = 500 A / 1 A
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