Almost 30 years, Neil Muncy, W3WJE, (the Pin One Guy), showed me and an
pro audio RFI colleague an in-house engineering report from a mfr of
large variable speed drives. They were having problems with RFI from the
drives screwing up the control circuitry from those drives, and
identified the wiring between controller drive as a principal mechanism.
The common thread was that the controllers and motors were widely
separated.
We were interested because RFI from drives running elevator motors was
getting into microphone circuits in large sound systems. A system Neil
was working on was at large performing arts center in NJ.
A few years later, at a church in Dayton where I was inspecting a sound
system I'd designed, I ran into an EE who specialized in EMC. We got to
talking, and the conversation turned to variable speed drives in large
installations. He volunteered that interconnecting wiring was the
culprit, and we agreed that all of the current-carrying conductors had
to be twisted pairs, which was the same solution Neil found. Obviously,
making the controller and motor a single integrated package is also a
great solution for smaller systems.
73, Jim K9YC
On 11/11/2024 12:12 PM, Gary Johnson via RFI wrote:
I wanted to mention one other good strategy that these new adjustable-speed drives are
using: For most of the motors, they integrate all the power electronics right into the
motor assembly, thus eliminating wires on the output side where the commutating
waveforms and high circulating currents are present. Then they are applying proper RFI
suppression to the incoming AC lines, again built right into the motor assembly. So
the potential antenna lengths are greatly reduced and I’m seeing how effective
this strategy actually is. The only motor without this approach is the big compressor,
and that has a HUGE filter network nearby and also twisted wires to the motor, all
inside a steel enclosure. Carrier was not being cheap or sloppy, and it shows.
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