J
I have a noise problem associated with a VFD/motor (75HP 460v wye start/delta run) system. This system (motor/drive) runs the blower to a concert hall. The low level lines (microphone lines) of which there are 200+ pick up to varying degrees the trash (noise) produced by the VFD.
We have tried a variety of solutions, including line reactors, drive isolation transformer, moving the VFD to an alternate location (closer to the motor).
We still have the noise...
We have established that the noise is not coming from the power input side of the audio system. We "believe"/"think" that the noise is broadcasted into the low level lines (mics/intercom)...Thses are shielde-ballanced lines, but they still see the trash....
We theorised that the VFD/motor current (50A) was radiating noise into mic lines that were roughly 10-15 feet away, but which ran paralell for 100+ feet. We then decided to test our theory by powering the VFD/motor via a 460v 3PH generator.
...SUCCESS!....but not really....
The audio system was quiet with the generator setup. We reasoned that the VFD/motor power should be fed via an alternate location...The parking garage next door, (3x125 feet of wire run), and away from all mic lines ... We hooked it up... The noise was back...
The "GROUND" issue...
From the beginning, the grounding concept was discussed... The concert hall building is one giant ground loop in my opinion. At every junction box the contractors tied the ground, "the little green wire", to the side of the box. It is certainly concievable that in the maze of electrical systems throughout the building, a "neutral" might be tied to ground (this would be additional to the neutral/ground connection at the service entrance). That could well be the magic wire (if it exists).
The VFD/motor is grounded, and is a likely source of at least part of the problem.
When the VFD/motor power was sourced from the parking garage the ground was left in it's orriginal location,-- tied to the building steel... The ground circuit does have a "copper path" back to the service entrance, but it is by no means isolated.
The audio system ground is (or at least appears to be), an isolated ground.
This e-mail was prompted by a 2002 discussion about floating 3PH systems...
Is it safe (for humans/hardware) to float the motor?... Should I tie the VFD to the motor, as it is at present, and disconnect those units from earth?... Keep in mind that we communicate to the drive via RS485 (232?)...
As I recall, I measured 3-5 amps from VFD/motor to ground....
The VFD is in an odd location, and certainly not optimal for a low noise installation. My current plan is to move the VFD very close to the motor (<20ft.), tye the motor to the VFD, and run a low impeadance ground (#2 welding cable) back to the parking garage earth stake.
Thanks for your time!
Joel Young
We have tried a variety of solutions, including line reactors, drive isolation transformer, moving the VFD to an alternate location (closer to the motor).
We still have the noise...
We have established that the noise is not coming from the power input side of the audio system. We "believe"/"think" that the noise is broadcasted into the low level lines (mics/intercom)...Thses are shielde-ballanced lines, but they still see the trash....
We theorised that the VFD/motor current (50A) was radiating noise into mic lines that were roughly 10-15 feet away, but which ran paralell for 100+ feet. We then decided to test our theory by powering the VFD/motor via a 460v 3PH generator.
...SUCCESS!....but not really....
The audio system was quiet with the generator setup. We reasoned that the VFD/motor power should be fed via an alternate location...The parking garage next door, (3x125 feet of wire run), and away from all mic lines ... We hooked it up... The noise was back...
The "GROUND" issue...
From the beginning, the grounding concept was discussed... The concert hall building is one giant ground loop in my opinion. At every junction box the contractors tied the ground, "the little green wire", to the side of the box. It is certainly concievable that in the maze of electrical systems throughout the building, a "neutral" might be tied to ground (this would be additional to the neutral/ground connection at the service entrance). That could well be the magic wire (if it exists).
The VFD/motor is grounded, and is a likely source of at least part of the problem.
When the VFD/motor power was sourced from the parking garage the ground was left in it's orriginal location,-- tied to the building steel... The ground circuit does have a "copper path" back to the service entrance, but it is by no means isolated.
The audio system ground is (or at least appears to be), an isolated ground.
This e-mail was prompted by a 2002 discussion about floating 3PH systems...
Is it safe (for humans/hardware) to float the motor?... Should I tie the VFD to the motor, as it is at present, and disconnect those units from earth?... Keep in mind that we communicate to the drive via RS485 (232?)...
As I recall, I measured 3-5 amps from VFD/motor to ground....
The VFD is in an odd location, and certainly not optimal for a low noise installation. My current plan is to move the VFD very close to the motor (<20ft.), tye the motor to the VFD, and run a low impeadance ground (#2 welding cable) back to the parking garage earth stake.
Thanks for your time!
Joel Young