Appendix B Component Sizing Calculations; Sizing Of Mcb For Switching Frequency Filter - Control Techniques Unidrive Regen Installation Manual

Appendix B
B.1

Sizing of MCB for switching frequency filter

The current rating of the MCB must be calculated; taking into account the switching frequency filter inductance and capacitance, the initial charging
current and the AC supply voltage. switching frequency filter inductance and capacitance values can be found in Chapter 5 Components on page 10.
L = 2 x Lf Lf = Switching frequency filter inductance
C = 3Cf / 2 Cf = Switching frequency filter capacitance
Vc = V peak Vc = Charging voltage
LL
L
Zc = Zc = Charging impedance
--- -
C
π
LC
Tc = Tc = Charging time
Ic = Vc / Zc Ic = Charging current
Example:
Unidrive size 5 Regen
Switching frequency filter Inductance 100µH
Switching frequency filter Capacitance 80µF
Supply Voltage 480v + 10%
L = 2 x 100µH =
C = 3 x 80µF / 2 =
480 + 10% x √2 =
Vc =
200µH
Zc = ----------------- - =
120µF
π
×
200µH 120µF
Tc = =
Ic = 747 / 1.29 =
The MCB should be rated to the peak charging current of 579A for 487µs, with an rms current of 35A. Refer to Table 5-6 for a full list of ratings. A
suitable MCB should have the following ratings and features:
Voltage rating:
Peak current rating: 579A
rms current rating: 35A
3 pole with auxiliary (for enable)
Table B-1
Power rating
Drive size
(kW)
1 4.0
5.5
2 7.5
11.0
15.0
18.5
3 22.0
30.0
37.0
45
55
4 75
90
110
5 150
36
Component sizing calculations
200µH
120µF
747V pk
1.29Ω
487µs
579A
480 + 10%
Total DC bus capacitance
1,100
1,100
2,200
2,200
2,200
3,300
3,300
4,400
6,600
6,600
8,800
www.controltechniques.com
(µF)
340
470
470
680
Unidrive Regen Installation Guide
Issue Number: 2