CIRCUTOR computer SMART III-Fast Series - Manual (Page 83)

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
4000/5 0�04 0�05 0�07 0�08 0�10 0�11
Forothervoltagesorconditionsnotincludedinthetable,thevalueofC/Kcanbeobtainedby
meansofasimplecalculation�
 Calculating the C/K Factor
TheequationforcalculatingtheC/Kfactoris:
V K
Q
K
I
K C C
⋅ ⋅
= =
3
/
where I c :isthesmallestcapacitorcurrent�
K:thecurrenttransformertransformationratio�
Tocalculate
Ic
itisnecessarytoknowthereactivepowerofthesmallestcapacitor Qandthe
networkvoltage V�
V .
Q
C
I
3
=
ThetransformationratioKiscalculatedas:
sec
I
prim
I K / =
whereIprim :isthenominalcurrentofthetransformerprimary�
Isec:isthecurrentofthetransformersecondary�
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
Ic:
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,
in which case the C/K value of the previous example would be 0.72.
IftheC/Kisconfiguredlowerthantheactualvalue,connectionsanddisconnec-
tions would occur continuously with few load variations (the system performs
moreoperationsthannecessary)�
IftheC/Kisconfiguredhigher,theregulatorrequiresahigherdemandforreac-
tivepowerinordertoswitchandperformfeweroperations�
83 Instruction Manual
Computer SMART III FAST