Installation and Connection
3-12 | CFW-11M G2
3
The harmonic input currents depend on the impedance values that are present in the rectifier input/output circuit.
The addition of a line reactor and/or DC bus choke reduces the current harmonic content, providing the following
advantages:
Increased input power factor.
Reduced RMS input current.
Reduced power supply voltage distortion.
Increased life of the DC Link capacitors.
To determine the line reactor needed to obtain the desired voltage drop, use equation below:
L
line
=
Voltage Drop [%] x Line Voltage [V]
3 x 2π x Line Freq [Hz] x Rated Cur . [A]
ATTENTION!
It is recommended a line reactance of at least 3 % on the input of the 6-pulse diode rectifier.
3.2.1.3 Pre-Charge
The resistors of the pre-charge circuit must be sized according to the following criteria:
Maximum voltage.
Maximum energy.
Power overload capacity of the resistors during the pre-charge period (energy dissipation capacity).
Table 3.5:
Dimensioning of the pre-charge
Peak Current During the Pre-charge (A)
0.82.(V
line
/R)
Energy Stored in the Capacitor Bank (J)
UP11-02 G2
N.0.012.V
line
2
UP11-01 G2
N.0.006.V
line
2
Duration of the Pre-charge (s)
UP11-02 G2
0.031.N.R
UP11-01 G2
0.015.N.R
Where R is the ohmic value of the resistor used on each phase and N the number of power units.
Example:
At a drive composed by three power units, whose line voltage at the input of the rectifier was 690 Vrms
(UP11-01 G2), the obtained values would be the following:
Energy stored in the capacitor bank: 3.0,006.6902 = 8569.8 J.
Using three 10 Ω resistors (one per phase), each resistor must withstand 2856.6 J.
The resistor manufacturer is able to inform the power supported by the component.
The peak current during the pre-charge would be 56.6 A and the length of the pre-charge would be 0.45 s.
