Topband: Gas well pump motor

[GEORGE WALLNER]

On Fri, 01 May 2009 20:49:11 -0600
  Art <k6xt at arrl.net> wrote:
> ...noisy pumps and their 
> cures. Last winter the gas wells on my place were
> converted to electric motors.

Art,

 From your description of the noise it is hard to say what 
generates it, but I got a feeling that it may come from a 
Variable Frequency Drive. These are essentially solid 
state AC power supplies that use a single phase 230 V AC 
input to generate a three phase 10 to 60 Hz variable 
frequency simulated AC output that is formed by a series 
of modulated 2 to 10 kHZ pulses. From the point of view of 
driving motors, they are fantastic: efficient, easy speed 
control, all kinds of programming features, etc. From an 
RFI point of view they are weapons of mass destruction! 
The inputs are easy to filter, just a regular RFI filter 
(Corcom, whatever), but the outputs require very special 
(and expensive) filtering and shielding. Once you have 
determined that it is a VFD that generates the noise, and 
you can get access to it, I will be happy to provide you 
details on the filtering of the outputs.

Unfortunately, we will be seeing these more and more 
often, not only in industrial applications but even in 
home appliances.

GL,

George
AA7JV