WEG CFW-10 - Line Reactor

102
CHAPTER 8 - OPTIONS AND ACCESSORIES
8.2.1 Application
Criteria
In a general manner, the CFW-10 series inverters can be
connected directly to the power supply line without line reactors. But
in this case, ensure the following:
To ensure the inverter expected life, a minimum line impedance
that introduces a voltage drop as shown in table 8.1, as a function
of the motor load, is recommended. If the line impedance
(transformers + wirings) is lower than these values, it is
recommended to use line reactor(s).
When it is necessary to add a line reactor to the system, it is
recommended to size it considering a 2 % to 4 % voltage drop (for
nominal output current). This pratice is results in a compromise
between motor voltage drop, power factor improvement and
harmonic current distortion reduction.
Always add a line reactor, when capacitors for power factor
correction are installed in the same line and near to the inverter.
Figure 8.2 shows the line reactor connection to the input.
Use the following equation to calculate the value of the line reactor
necessary to obtain the desired percentage of the voltage drop:
8.2 LINE REACTOR
Due to the input circuit characteristic, common to the most inverters
available on the market, consisting of a diode rectifier and a capacitor
bank, the input current (drained from the power supply line) of inverters
is a non sinusoidal waveform and contains harmonics of the funda-
mental frequency (frequency of the power supply: 60 Hz or 50 Hz).
These harmonic currents circulate through the power supply line and
cause harmonic voltage drops which distort the power supply voltage
of the inverter and other loads connected to this line. These harmonic
currents and voltage distortions may increase the electrical losses in
the installation, overheating the components (cables, transformers,
capacitor banks, motors, etc.), as well as lowering the power factor.
The harmonic input currents depend on the impedance values that
are present in the rectifier input/output circuit.
The installation of a line reactor reduces the harmonic content of the
input current, providing the following advantages:
Increasing the input power factor;
Reduction of the RMS input current;
Reduction of the power supply voltage distortion;
Increasing the life of the DC link capacitors.
where:
 V - Desired line voltage drop, in percentage (%);
V
e
- Phase voltage at inverter input (line voltage), given in
Volts (V);
I
e,nom
- Input inverter rated current (refer to Chapter 9);
f - Line frequency.
L = 1592 .

V .
V
e
[H]
(f . I
e, nom
)