OT: VSD's and DC power

[leitmotif]

It is a good idea, and one I had briefly considered. The problem is that that would need me to completely redo the entire crane electrics, which is way outside the allowable scope. The other problem is that there is more than one crane on these rails, and only one can be out of service at any one time, due to the criticality of the process.

It is a very interesting project, with a lot of dimensions. Thanks to everyone for the discussion thus far.

Chris
I think Dicks idea is worthy of merit.

Leaving existing DC system will require jacking DC voltage 240 VDC to accomodate the DC bus voltage of VFDs 325 VDC if using 230 VAC motors and 650 VDC if using 460 VAC motors. This may take you out of the design voltage allowance of your collectors and rail system.

Switching the existing rail system and collectors to 240 single phase AC will
keep the system at near design voltage.
eliminate the equipment to jack the DC voltage
not effect the changes you will make to cab controls -- VFD fed from DC line or an AC line will take the same controls anyway.

This place sounds like a steelmill I used to work at here in Seattle.
Dan Bentler

 

[zankorel]

Chris
I think Dicks idea is worthy of merit.

Leaving existing DC system will require jacking DC voltage 240 VDC to accomodate the DC bus voltage of VFDs 325 VDC if using 230 VAC motors and 650 VDC if using 460 VAC motors. This may take you out of the design voltage allowance of your collectors and rail system.

Switching the existing rail system and collectors to 240 single phase AC will
keep the system at near design voltage.
eliminate the equipment to jack the DC voltage
not effect the changes you will make to cab controls -- VFD fed from DC line or an AC line will take the same controls anyway.

This place sounds like a steelmill I used to work at here in Seattle.
Dan Bentler

It is for an Aluminium smelter potline. As i said, the process will not allow all the cranes to be put out of service for the duration required. In any case, I only have approval to do one crane at the present moment.
The plan is not to touch the voltage at the collector rail, but install the voltage step up (along with the rest of the new electrics) on the crane gantry. This will mean it will not affect the operation of the other cranes.

 

[rpoet]

Just thinking:
Assuming a drive would be happy with such a low bus voltage (240vdc) could one not set a custom v/Hz curve in the drive, and then use either a custom motor designed for the lower voltage, or possibly a step-up transformer between the drive and motor?

I understand there might be practical issues with the transformer plan, such as the transformer's behavior at different frequencies. That does beg a question though - since a drive's "output frequency" is actually synthesized via PWM at a much higher frequency, would a step-up transformer actually care?

More questions than answers, but just thinking...

-rpoet