3.5
How to choose the CURRENT TRANSFORMER (C.T.)
Use a Current Transformer (C.T.) with 5A at secondary circuit and primary
equal or slightly higher than the maximum absorbed by the loads. The C.T.
must be chosen in such a way to obtain a good current signal in the
secondary circuit. Current values between 0.5 and 5Amps are suitable to
obtain good working conditions of the regulator.
The C.T. must be good quality (first class) and with power equal or higher
to 5VA. If the C.T. has been mounted far from the equipment, it needs to
add the normal demanded the power consumed from the cables of connection
(normaly 0.2VA per meter of bifilar lines with 2.5mm
2
section) and the power
dissipated by others possible tools connected in the circuit.
The equations, used to calculate the real losses, are the sequents:
R = 2 x x L/S
(
Ω
)
Total resistance of amperometric circuit
P=(R+0.08) x I
2
(VA)
L o s s e s o f a m p e r o m e t r i c a l c i r c u i t
‘ ’ is the electrical resistivity ( 0.018 for the copper )
‘L’ is the length of amperometric circuit (mt)
‘S’ is the across section of cables at the secondary of TA
‘I’’ is Imax. at the secondary of C.T.
‘0.08’ are the internal resistance of P.F. regulator
When single-phase inductive loads are connected (unbalanced three-phase
system), place C.T. on the phase where Power Factor is lower and/or where
higher current value is absorbed.
The cables at the secondary of C.T. have to be of 2,5mm
2
section.
The C.T. connection must not to be protected with fuses or interruped by
switch.
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