fixed coils the grid are recognized
. The measurement
usually takes 240 ms.Page 185
Commissioning current injection
YU
BC
UNE
BL
YW
IU
ICI f1,f2
Figure 117: Simplified equivalent circuit with current injection unequal Hz
The simplified equivalent circuit with current injection Figure 116 produces the equiva-
lent circuit Figure 117 when current with frequency unequal injected.35)
1 2
_ 2
2 2
1 2
( )
CI f
imag imag Y
C
(1.37)
Based the assumption that the system linear, both frequencies can injected the
same time.
The system's conductance viewed from the current injection point can formulated
for current injection follows:
_
_
_
1
( )
CI fn
W n
CI U
n
NE fn
I
Y C
U L
(1.33)
For symmetrical grids with small YU, this results in:
_
_
_
1
( )
CI fn
W n
CI fn
n
NE fn
I
Y C
U L
(1.34)
If two frequencies and are used, two complex equations with three variables are creat-
ed and can used calculate the grid parameters, without adjusting the P-coil. The corresponding value _
CI fn
Y can also determined the same time, mak-
ing possible quickly measure and determine the grid parameters.36)
_ 1
1 1
1
( )
CI f
L
imag C
(1. This
approach leads the following solutions:
1
_ 1
f
W
NE f
I
Y real
U
(1.
A list the main method advantages contains:
0 Very fast measurement change the grid topology unlikely during the measure-
ment time
0 The process can used very symmetrical grids
0 All P-coils incl
