Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 23)

Overview of Drive 1-5
7000 “C” Frame 7000L-UM300I-EN-P – June 2013
Rectifier Designs
There are two offered designs for the front-end rectifier of the 7000L
“C” Frame 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-pulse or 12-pulse offerings in terms of lowering line
side harmonics.
The isolation transformers are available in both indoor dry type 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.)
The 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 the 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)