On Wed, 08 Apr 2009 17:59:04 -0700
"Jim Brown" <jim@audiosystemsgroup.com> wrote:
> On Wed, 08 Apr 2009 19:12:16 -0400, w2pm@aol.com wrote:
>
> I don't know, but my guess would be yes. If you are on
>good terms with your
> neighbor, you may get some relief with a good line
>filter.
If the motor is supplied via a variable frequency drive
(VFD) it will require some special filtering! These drives
input single phase (but sometimes three phase) 230 V 60 Hz
AC and output a vartiable frequency (10 to 70 Hz)
simulated three phase 230 V AC that is generated using
streams of constantly modulated 2 to 10 kHz pulses.
Filtering the input is relatively simple: as Jim said, a
good Corcom filter will do it. You can not, however put
one those filters on the outputs! The high value
capacitors in the filters will load the outputs too much
(10 kHz!), the filters get hot, the VFD gets hot and the
motor will not run properly. (Indeed the drive's internal
CPU may shut if off.) You need to install a two stage
filtering system: first, connect to the output what is
called a reactor. It is essentially a three wire very low
frequency common mode choke (see Newark.com). Following
the reactor, you need to install three 2200 pF, 1 kV mica
or ceramic capacitors, one between each output line and
ground. That should be followed by a HF common mode choke
that consists of about 8 turns of three wires (suitably
sized and insulated) wound as a common mode choke on a 2"
ferrite ring (No. 31 or similar), followed by another
three capacitors. Now to top if off, you need to run the
power to the motor using either a shielded "frquency
drive" cable (amazingly expensive!) or three separate
RG-58 coax lines, where the inner conductors carry the AC
power and the shields are tied to ground. Good grounding
is essential! Shielding the whole thing will help too. I
have done all that, and it sort of works! VFD's are high
power (100W+) noise generators! There is a good tutorial
on VFD's on the omega.com web site.
GL,
George
AA7JV
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