[RFI] RFI from variable speed drive 1.1 miles away (very interesting case).

[Jim Brown]

On 11/17/2022 7:52 AM, Wes Stewart via RFI wrote:
>   This is very interesting to me as I've posed an earlier, as yet unanswered, question about potential RFI in a Bosch inverter-driven compressor heat pump,.  I am considering this as an alternative to a two-speed conventional compressor unit.  The Bosch is addition to the government mandated ECM blower also uses variable speed condenser fan.  The schematic shows a couple of toroid chokes on the line input, so they've made some attempt at suppression but how effective, who knows.

The analysis I've heard from two very competent engineers (the late Neil 
Muncy, and an industrial consultant who had encountered VFDs in the 
wild) is that a major mechanism is the magnetic field produced by 
current loops in the path between the controller and the motor.  Both 
Neil and that EE noted that it is common for motor and controller in 
industrial installations to be widely separated. If there IS a twisted 
pair, the resulting transmission line will confine HF currents to it, 
but if it's NOT, a strong magnetic field will be produced in the random 
return path depending on "ground" between motor and controller, in 
addition to the EM field which radiates.

This is in addition to "Pin One-like" problems with termination of the 
mains "green wire" at the chassis at the point of entry, or not. In 
products with line filters, it's pretty common for noise current to be 
emitted on the green wire, which radiates.

73, Jim K9YC