Technical data

June 2008
40-216
For more information visit: www.eaton.com CA08102001E
Adjustable Frequency Drives
40
CFX9000
Enclosed Drives
4. Clean Power 18-Pulse Drives
When the total load is comprised of non-linear load such as
drives and the ratio is Isc/I
L
, the greatest harmonic mitiga-
tion is required. Under these conditions, the currents drawn
from the supply need to be sinusoidal and “clean” such that
system interference and additional losses are negligible. The
Cutler-Hammer CPX9000 Clean Power Drive uses a phase-
shifting auto transformer with delta-connected winding that
carries only the ampere-turns caused by the difference in
load currents. This results in nine separate phases. In this
type of configuration, the total KVA rating of the transformer
magnetic system was only 48% that of the motor load.
A traditional isolated transformer system, with multipulse
windings, would require the full KVA rating to be supported,
which is more common in a MV step-down transformer.
The integrated 18-pulse clean power drive, with near sine wave
input current and low harmonics will meet the requirements
of
IEEE 519-1992 under all practical operating conditions. The
comparisons with 6-pulse, passive filter and 12-pulse, systems
are shown in Figures 40-116, 40-120, 40-122 and 40-124.
Figure 40-123. Basic 18-Pulse Rectifier with Phase-Shifting Auto-Transformer
Figure 40-124. 100 hp 480V Drive with 18-Pulse Rectifiers
Table 40-317. 100 hp 480V Drive with 18-Pulse Rectifiers
Advantages
Effectively guarantees compliance with IEEE 519-1992
Provides increased input protection for AFD and its semi-
conductors from line transients
Up to 4 times the harmonic reduction of 12-pulse methods
Smaller transformer than isolation transformer used in
12-pulse converter
Minimizes ripple current in capacitors, doubling expected
capacitor life
Disadvantages
Larger and heavier magnetics than some other methods
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
A
C
N
Output Transistors
IGBT Section
Dynamic Braking
Tra nsistor
Pre-charge
Circuit
18-Pulse SCR
Bridge Rectifier
Converter Section
18-Pulse
Phase-Shifting
Auto-Transformer
Inverter Section
(
) DC
(
+
) DC
Diode Rectifiers
Bus
Capacitors
3-Phase
AC Input
1
2
3
AC
Motor
18-Pulse Clean Power
Current Harmonics
I
1
= 100% I
11
= 0.24% I
19
= 1.00%
I
5
= 0.16% I
13
= 0.10% I
23
= 0.01%
I
7
= 0.03% I
17
= 0.86% I
25
= 0.01%
Power = 100 hp
H
c
= 5.9 Amps
200
Current
Amps
100
0
-100
-200
Time