Table 47:C/K factor (table 2)�
CT Ratio
(Ip / Is)
Power of the smallest stage at 440 V (in kvar)
2�5
5�0
7�5 10�0 12�5 15�0 20�0 25�0 30�0 40�0 50�0 60�0 75�0 80�0
150/5
0.09 0.18 0.27 0.36 0.45 0.54 0.72 0.90
200/5
0.07 0.14 0.20 0.27 0.34 0.41 0.54 0.68 0.81
250/5
0.05 0.11 0.16 0.22 0.27 0.33 0.43 0.54 0.65 0.87
300/5
0.05 0.09 0.14 0.18 0.23 0.27 0.36 0.45 0.54 0.72 0.90
400/5
0.07 0.10 0.14 0.17 0.20 0.27 0.34 0.41 0.54 0.68
0.81
500/5
0.05 0.08 0.11 0.14 0.16 0.22 0.27 0.33 0.43 0.54
0.65 0.81 0.87
600/5
0.05 0.07 0.09 0.11 0.14 0.18 0.23 0.27 0.36 0.45
0.54 0.68 0.72
800/5
0.05 0.07 0.08 0.10 0.14 0.17 0.20 0.27 0.34
0.41
0.51 0.54
1000/5
0.04 0.05 0.07 0.08 0.11 0.14 0.16 0.22 0.27
0.33 0.41 0.43
1500/5
0.04 0.05 0.05 0.07 0.09 0.11 0.14 0.18
0.22 0.27 0.29
2000/5
0.04 0.05 0.07 0.08 0.11 0.14
0.16 0.20 0.22
2500/5
0.04 0.05 0.07 0.09 0.11
0.13
0.16 0.17
3000/5
0.04 0.05 0.05 0.07 0.09
0.11
0.14 0.14
4000/5
0.04 0.05 0.07
0.08 0.10 0.11
For other voltages or conditions not included in the table, the value of C/K can be obtained by means
of a simple calculation.
Calculating the C/K Factor
The equation for calculating the C/K factor is:
V
K
Q
K
I
K
C
C
⋅
⋅
=
=
3
/
where
I
c
: is the smallest capacitor current.
K
: the current transformer transformation ratio.
To calculate
I
c
it is necessary to know the reactive power of the smallest capacitor
Q
and the network
voltage
V
.
V
.
Q
C
I
3
=
The transformation ratio K is calculated as:
sec
I
prim
I
K
/
=
where
Iprim
: is the nominal current of the transformer primary.
Isec
: is the current of the transformer secondary.
Example:
In a 400 V unit the smallest capacitor is of 60 kvar with a current transformer having a ratio
of 500/5, and the calculation would be made as follows:
Current of the smallest capacitor
I
c:
A
I
C
6
,
86
400
3
60000
=
⋅
=
K
Factor
100
5
/
500
=
=
K
The C/K value is:
0.866
.
If the power of 60 kvar is referenced at 440 V, it should be multiplied by Vgrid
2
/440
2,
80
Computer SMART III FAST
Instruction Manual
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