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Design
●
Calculating the Equivalent Capacity per Inverter
The equivalent capacity for an inverter is calculated as follows:
Equivalent capacity = Inverter's rated input capacity (Pi) x Coefficient
Here, the Inverter's rated input capacity (Pi) is calculated based on the rated capacity of the appli-
cable motor, as shown in the following table.
Inverter's Rated Input Capacity
Motor capacity
(kW)
0.4
0.75
1.5
The coefficient is as shown in the following table for a three-phase general-purpose inverter.
3
Three-phase
3-1 No reactor
bridge (capaci-
3-2 Reactor on AC side
tor smoothing)
3-3 Reactor on DC side
3-4 Reactors on AC and DC side
Calculating the Harmonic Current per Inverter
■
Use the following formula: nth harmonic current [A] =
Fundamental frequency input current [A] x nth harmonic current ratio (%)/100
Here, the values in the following table are used for the fundamental frequency input current and
converted for a received voltage of 6.6 kV.
Applicable motor [kW]
Fundamental frequency
input current [A]
Value converted for 6.6 kV [mA]
The following table is used to obtain the nth harmonic current ratio (%). Normally calculations are
performed only for the 5th and 7th harmonics.
Three-phase Bridge (Capacitor Smoothing)
Harmonic number
No reactor
Reactor on AC side
Reactor on DC side
Reactors on AC and DC side
Rated input capacity (Pi)
(kVA)
200 V
0.57
0.97
1.95
0.4
200 V
1.61
400 V
0.81
49
5
7
11
65
41
8.5
38
14.5
7.4
30
13
8.4
28
9.1
7.2
400 V
K
= 3.4
General-purpose inverters
31
Servo amplifiers
K
= 1.8
32
Elevators
K
= 1.8
33
Refrigeration and air condi-
K
= 1.4
34
tioning equipment
Other general-purpose
equipment
0.75
1.5
2.74
5.50
1.37
2.75
83
167
13
17
19
7.7
4.3
3.1
3.4
3.2
1.9
5.0
4.7
3.2
4.1
3.2
2.4
Chapter 2
(Unit: %)
23
25
2.6
1.8
1.7
1.3
3.0
2.2
1.6
1.4
2-35
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