Requirement of Load filter (DV/DT) for VFD output if motor is far away

[Shahzad]

NOTE: this is exclusive for inverter duty motors.
I have come across bunch of post on line where some recommend to install dv/dt (load filter) if motor distance is greater than 300 ft. However, some recommend to install load reactor if distance is greater than 500 ft.

Is there any standard or rule of thumb when to include load filter reactor at output of VFD? At what distance we should consider it?

 

[petersonra]

NOTE: this is exclusive for inverter duty motors.
I have come across bunch of post on line where some recommend to install dv/dt (load filter) if motor distance is greater than 300 ft. However, some recommend to install load reactor if distance is greater than 500 ft.

Is there any standard or rule of thumb when to include load filter reactor at output of VFD? At what distance we should consider it?

When it becomes financially attractive to the guys selling you these devices.

There's a difference between the filter and the reactor though. They are two different things.

 

[bwat]

Length is Manufacturer dependent. And sometimes even frame size dependent within same drive family from a manufacturer. There isn’t a one size fits all length where one makes sense over the other or where one is needed.

 

[milldrone]

Length is Manufacturer dependent. And sometimes even frame size dependent within same drive family from a manufacturer. There isn’t a one size fits all length where one makes sense over the other or where one is needed.

In appendix A of this document you will find wire distances for allen bradley drives.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjdvb7EtOLxAhVM-Z4KHVBQDsIQFnoECAMQAA&url=https%3A%2F%2Fliterature.rockwellautomation.com%2Fidc%2Fgroups%2Fliterature%2Fdocuments%2Fin%2Fdrives-in001_-en-p.pdf&usg=AOvVaw2f6Pztgm1OPBhrs3imDoXV

 

[junkhound]

re:
Length is Manufacturer dependent

You can hook up your scope to the VFD and see what the switching frequency and rise time is. Then measure motor parameters and shaft/frame capacitance when running on oil film.
Now you can calculate what filter to design to keep motor peak voltages below partial discharge inception to protect winding insulation and below oil film breakdown to prevent bearing damage.

have fun!

 

[Shahzad]

When it becomes financially attractive to the guys selling you these devices.

There's a difference between the filter and the reactor though. They are two different things.

Correct, I meant to write Dv/DT filter.

re:
Length is Manufacturer dependent

You can hook up your scope to the VFD and see what the switching frequency and rise time is. Then measure motor parameters and shaft/frame capacitance when running on oil film.
Now you can calculate what filter to design to keep motor peak voltages below partial discharge inception to protect winding insulation and below oil film breakdown to prevent bearing damage.

have fun!

That might be possible with existing running system but what if we are designing new system?

 

[bwat]

...but what if we are designing new system?

Again, read the manual from the manufacturer. Here's a snip for example that shows the lengths using the various reactors or filters and for what frame size:

 

[Besoeker3]

FWIW we always dv/dt filters. For us it was a low cost issue. And a lot of our applications were water sites with longer runs.

 

[Jraef]

Not a hard and fast rule, but if there are a lot of unknowns, I use >500’ for dV/dT filters, >3,000’ for sine wave filters. But I also weigh the cost of replacing the motor. For example on deep well submersibles where it can easily cost >$15k just to pull the pump out, a $1k filter is dirt cheap.