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. This
approach leads the following solutions:
1
_ 1
f
W
NE f
I
Y real
U
(1.35)
1 2
_ 2
2 2
1 2
( )
CI f
imag imag Y
C
(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.36)
_ 1
1 1
1
( )
CI f
L
imag C
(1. fixed coils the grid are recognized
.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.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.37)
Based the assumption that the system linear, both frequencies can injected the
same time. The measurement
usually takes 240 ms. The corresponding value _
CI fn
Y can also determined the same time, mak-
ing possible quickly measure and determine the grid parameters.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
