Snubber Circuit ??

[roberged]

We have an outdated drive system that we are looking to upgrade. Currently we have a 40 HP AC drive running a 20 HP motor, with 6 other drives (4-5 H.P. and 2-1 H.P.)being fed from this drives DC bus. We are having a difficult time finding the exact replacement for the 40 HP unit and would like to put a 20 HP drive in its place. There is also a snubber circuit wired to the this drive. First question is what it the snubber circuits purpose? Secondly if we remove the DC bus feed from the smaller drives and re-feed them with 3phase 480V and replaced the 40hp with the a new 20hp inverter will we still need the snubber circuit?
Thanks

 

[Skogsgurra]

roberged,

Snubbers are not common in VFDs. It could be that they are used to reduce the travelling wave overvoltage that occurs if you have a long cable between drive and motor.

I see no direct connection between the arrangement with smaller inverters being fed from the larger drive's DC bus and the use of a snubber. So the new drive configuration should not influence the use of snubbers.

If your motor cable is long or if the motor has a non-VFD winding (old insulation system), keep the snubbers - or insert motor reactors - to avoid overvoltage and corona (partial discharge) in your motor.

 

[charlierod]

Snubber circuits are used to protect power electronic devices against dangerous overvoltages.

It doesn´t matter if you replace actual devices in service because new ones also need protection.

 

[DickDV]

I suspect that the snubber being referred to here is a DC Bus Brake snubber, sometimes called a brake chopper and resistor. If that is the case, then, you must analyse how motoring and braking energy is flowing between the drives on the common bus and either reproduce the shared bus system as designed or deal with the braking energy on each drive that has braking requirements.

Usually, the shared DC bus is an economical way of avoiding lots of braking modules by sharing braking energy with other drives that are motoring at the same time. To the extent that this transfer of braking energy is possible, you avoid the need for brake snubbers on each drive.

I would proceed with caution is upsetting the original shared DC bus system.