Mitsubishi Electric FR-A700 Technical Manual page 478

Circuit components
Without reactor
Three-phase bridge With reactor (AC side)
(capacitor smoothing) With reactor (DC side)
With reactors (AC, DC sides)
(a) If the outgoing harmonic current is higher than the maximum value per 1kW (contract power)
power, a harmonic suppression technique is required.
3) Specific calculation example
When a 30kW 400V motor is driven by the FR-
A740-30K inverter
Fundamental wave current of the inverter is
49.0A
Rated capacity
fundamental
=
V
wave current
=
400
= 34.7 [kVA]
6-pulse equivalent capacity
=Rated capacity
=34.7 3.4 = 118 [kVA]
Since this value exceeds 50 [kVA], the inverter
is covered by the guideline.
Degree
Outgoing current [mA]
Maximum value of
outgoing current [mA/kW]
If the contract power is less than 965/3.5= 276kW, harmonic suppression techniques are required.
4) Harmonic reduction techniques
(a) Reactors for inverter (ACL, DCL)
Install a reactor (ACL) on the AC side of the
inverter or a reactor (DCL) on its DC side or
both to reduce outgoing harmonic currents.
Generally, installation of the reactor in only
one side of the inverter often produces an
insufficient suppression effect.
(b) Installation of
capacitor
When used with a series reactor, the power
factor improving capacitor has an effect of
absorbing harmonic currents.
This power factor improving capacitor may be
installed in either a high or low voltage side.
(c) Transformer multi-phase operation
When two transformers are used, connecting
them with a phase angle difference of 30
degrees as in
produce an effect corresponding to 12 pulses.
Harmonic content (Values of the fundamental current is 100%)
Degree
factor
-3
49.0 1.0228 10
conversion factor Ki
5th 7th
965 609
3.5 2.5
power factor improving
- , - combination will
5th 7th 11th
65 41 8.5
38 14.5 7.4
30 13 8.4
28 9.1 7.2
Hence, find the outgoing harmonic current in the
following procedure:
Rated current converted from received power
voltage
Fundamental
=
-3
wave current
10
=49.0
Outgoing harmonic current
current
Converted from
=
received power
voltage
It is derived from the following table.
Assume that the operation ratio is 50%.
11th 13th 17th
126 114 63.9
1.6 1.3 1.0
In this case, it is ideal that the harmonic
generating equipment of the load of each
transformer is the same in model and
capacity. If the capacity differs, however, a
12-pulse effect for smaller-capacity equipment
can be expected. Therefore, the conversion
factor for 6-pulse reference is halved.
(d) AC filter
A capacitor and a reactor are used together to
reduce impedances at specific frequencies,
producing
harmonic currents.
The AC filter exhibits an effect on a specific
frequency. When there is more than one
harmonic current degree, the AC filter must be
installed for each degree.
512
SELECTION
13th 17th 19th
7.7 4.3 3.1
3.4 3.2 1.9
5.0 4.7 3.2
4.1 3.2 2.4
(400V/received voltage)
400/6600 = 2.97[A]
operation harmonic
ratio content
19th 23rd 25th
46.0 38.6 26.7
0.9 0.76 0.70
a great effect
(Unit: %)
23rd 25th
2.6 1.8
1.7 1.3
3.0 2.2
1.6 1.4
contract
-3
10 [mA]
of absorbing