Rockwell Automation 7000L PowerFlex 7000 Medium Voltage AC Drive C Frame - Marine - Manual (Page 18)

1-4 Overview of Drive
7000L-UM302B-EN-P – June 2013 7000 “C” Frame - Marine
Rectifier Designs
There are two offered designs for the rectifier of the PowerFlex 7000L
drive.
18-Pulse Rectifier
An 18-pulse phase controlled rectifier is shown in Figure 1.2. In an
18-pulse configuration, the IEEE 519-1992 requirements are met in
the majority of cases without the need for passive filters; however, a
multi-winding isolation transformer is required to mitigate the low
order harmonics by phase shifting principles. The 18-pulse solution is
superior to 6- or 12-pulse offerings in terms of lowering line side
harmonics.
Isolation transformers are available in indoor dry type, cast coil, and
outdoor oil-filled designs for maximum flexibility in dealing with floor
space, installation costs, and control room air conditioner loading.
(Refer to Specification 80001-005, Rectifier Duty Transformers, for
more details on transformer requirements and features.)
Sample line current and voltage are also shown in Figure 1.2. The
THD of line current is approximately 5.6%, while the THD of line
voltage (line-to-line) is approximately 2.0%. (THD of line voltage is
a function of system impedance.) The 18-pulse rectifier consists of
one master bridge and two slave bridges and will always have a total
of 18 SCR switching devices.
Figure 1.2 – 18-pulse Rectifier and its input waveforms
a) Line current
b) Line-to-line voltage at PCC
a)
b)