VFD to DBR Distance 1

[sunrays]

Is there any cable length limitations between a VFD and its DBR? Most manuals speak of VFD to Motor cable lengths only.

I have an application that is a highly overhauling load with the DBR in circuit for a good 1 minute in every 3 minutes. This results in the DBR temperature to raise to around 150 Deg. C. To avoid radiation of this heat on to the VFD panel located close by I propose to shift this DBR to a remote location with a cable distance of around 100 meters.

Are there any known issues on this issue.

Thanks in advance

 

[jraef]

None, other than voltage drop, which in this case actually helps. the power to the DBR is going to be strictly DC, no pulses to worry about.

 

[ozmosis]

phew, 100M? There would be a few issues I can think of.
1) You are adding to the resistance of the whole circuit so the ability to dissipate the required power will be reduced [Increased resistance=lower power dissipation. Lower resistance=higher power dissipation but the brake chopper (transistor) will require a higher current rating]
2) Be aware, you are looking at high voltages on this cable (nominal 400VAC supply you will be looking at anything upto 750VDC on this cable). It will certainly need to run in a protected cable (conduit, armoured).
3) A VFD will have no EMI filtering on your DC link. 100M of cable directly connected to your DC link will route high frequency interference everywhere that cable goes. Special precautions needed for segregation etc.
4) The added inductance could induce resonance on the DC link. Difficult to determine but this could be problematic.

We would normally advise no longer than 10M.

 

[sunrays]

Thanks sed2developer!

I have considered armoured cable and well segregated from other cables. I have no choice but to run this cable as the DBR temperature raise could not only affect the VFD but the room ventilation system as well.

I will also reduce the resistance value in the DBR marginally to compensate for the cable resistance there by ensuring that the total resistance is within the value specified in the manufactures manual. That should take care of the power dissipation ability I guess.

 

[DickDV]

Use the same brake chopper and be sure to place the resistor leads in metal conduit.

Otherwise, I think you will be ok. Unlikely that noise issues will come up since the DC bus is already heavily swamped with capacitance.

 

[sunrays]

The brake chopper is integral to the VFD.

Any way I have decided to change the location of the DBR. I will revert back with the outcome shortly.

 

[Drivesrock]

Hi Sunrays

My recommendations for your application would be;

You may have to install the resistor bank remote to the drive for fire / safety reasons - ie Insurance company will not accept the resistor banks in the same electrical room as the drive or perhaps to reduce the air conditioning of the room. 100metres though, seems excessive.

1. When installing the DBR remote from the cubicle with the drive and 'chopper' use fuses between them to protect against short circuits.
2. Use parallel conductors or twist them together to reduce the inductance.
3. The DBR must have a thermostat and this should be wired in series to an input contactor to the drive. If the resistor bank gets too hot then the drive will be shutdown. Donot just use the thermostat to trip the drive. If the DB Chopper goes faulty - transistor (or its anti-parallel diode) short circuit for example (and it does happen!) - then the resistor will be connected straight across the dc link and will be on all the time. Use an auxiliary contact off the incoming contactor to trip the drive.
4. Select non-inductive resistances
5. Keep the dc cables segregated from other power and signal cables
6. Make sure all the equipment is properly earthed.

Hope this helps!