Hi Scott,
I can't answer your question about a consultant, but let me make some
comments based on a few cases of VFD and AC Servo Drive interference I've
had to deal with as a ham as well as some of my day job experience with
VFDs and the likes (over the years I've done a fair amount of electrical
control system design for some of the manufacturing equipment that we use
in development as well as production).
In the cases of RFI I've encountered as a ham, the biggest issue is that
the system integrator (company designing the electrical controls package
that included a VFD in the design) did not include the input power line
filter that the VFD manufacturer said was was required to make their VFD
EMC compliant (most system integrators totally ignore the recommended power
line filter in their design). Turns out that a lot of the VFD
manufacturers know what it takes to make their VFD EMC compliant and
document this in their manuals, but users of their drives are clueless and
often ignore their recommendations.
One case involved a VFD that was driving a commercial kitchen ventilation
fan motor at a large apartment complex near my house. After I identified
the VFD as the source of my RFI they went back and installed the power line
filter recommended by the VFD manufacturer, and this fixed my RFI issue.
In another case the owner of an injection molding facility did not want to
spend $955 for the power line filter recommended by the AC Servo Drive
manufacturer to address the RFI I was encountering, so I spec'd an
inexpensive 3 phase input power line filter (Delta Electronics model
30TDVST2) that cost $77 that they could try to see if it had any effect on
the RFI but I told them I was not liable for their decision making. They
purchased and installed the Delta Electronics filter that I specified and
this fixed the RFI issue. They installed another identical injection
molding machine and it also caused RFI so they installed the same filter on
this second machine and once again it eliminated the RFI. The injection
molding machine manufacturer eventually reimbursed the injection molding
house for the filters they purchased.
Note: in cases where the motor is located a considerable distance from the
drive I know there are techniques that should be considered regarding the
cables going from the drive to the motor (well bonded conduit, special
shielded cabling, etc.). For any VFD that is part of the design I would
have someone review the VFD manual to see what filter is specified to make
the drive EMC compliant and if this information is not included in the
manual then someone needs to contact the VFD manufacturer for this
information. If they can't provide this information then I would be
hesitant in using their drives in the design or I would at least specify a
good power line filter. I've also seen toroid cores available for use with
VFD systems as chokes (on the input and/or output side of the drive) in
addition to using traditional power line filters.
Just FYI, and good luck.
Don (wd8dsb)
On Tue, Jul 13, 2021 at 3:28 PM nm8rmedic via RFI <rfi@contesting.com>
wrote:
> All,I am the Manager of a mid-sized municipality. We are installing VFD's
> at an existing sewer lift station, replacing soft-starts, on a pair of 40
> hp pump motors.I'm inquiring if anyone in this group could point me at a
> consultant who could advise the engineer drafting the specifications for
> this retrofit, in regard to RFI/EMI mitigation and best practices.ScottSent
> via the Samsung Galaxy S8+, an AT&T 5G Evolution capable smartphone
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