Technical data

June 2008
40-244
For more information visit: www.eaton.com CA08102001E
Adjustable Frequency Drives
40
CPX9000
Enclosed Drives
2. 12-Pulse Converters
A 12-pulse converter incorporates two separate AFD input
semiconductor bridges, which are fed from 30º phase shifted
power sources with identical impedance. The sources may
be two isolation transformers, where one is a delta/wye
design (which provides the phase shift) and the second a
delta/delta design (which does not phase shift). The 12-pulse
arrangement allows the harmonics from the first converter
to cancel the harmonics of the second. Up to approximately
85% reduction of harmonic current and voltage distortion
may be achieved (over standard 6-pulse converter). This per-
mits a facility to use a larger percentage of AFD loads under
IEEE 519-1992 guidelines than allowable using line reactors
or DC chokes. A harmonic analysis is required to guarantee
compliance with guidelines.
Figure 40-142. Basic 12-Pulse Rectifier with “Phase Shifting” Transformer
Figure 40-143. 500 hp 480V Drive with 12-Pulse Rectifier
Table 40-356. 500 hp 480V Drive with 12-Pulse Rectifier
Advantages
Moderate cost, although significantly more than reactors
or chokes
Substantial reduction (up to approx. 85%) in voltage and
current harmonics
Provides increased input protection for AFD and its semi-
conductors from line transients
Disadvantages
Impedance matching of phase shifted sources is critical to
performance
Transformers often require separate mounting or larger
AFD enclosures
May not reduce distribution harmonic levels to below
IEEE 519-1992 guidelines
Cannot retrofit for most AFDs
12-Pulse Diode
Bridge Rectifier
Converter Section
Inverter Section
(+) DC
L1A
L2A
L3A
L1B
L2B
L3B
(-) DC
Dynamic Braking
Tra nsistor
Output Transistors
IGBT Section
AC
Motor
12-Pulse Diode
Bridge Rectifier
Converter Section
12-Pulse
Phase Shifting
Tra nsformer
Bus
Capacitors
12-Pulse Circuit
Current Harmonics
I
1
= 100% I
11
= 4.19% I
19
= 0.06%
I
5
= 1.25% I
13
= 2.95% I
23
= 0.87%
I
7
= 0.48% I
17
= 0.21% I
25
= 0.73%
Power = 500 hp
H
c
= 66.2 Amps
1000
Current
Amps
500
0
-500
-1000
0.126 0.13225 0.1385
Time in Seconds
0.14475 0.151