OT: Frequency drive location remote mounted or panel

Hi all - off topic but anyway......

We are looking at installing a new bottle line and I am curious to hear what the trend is with frequency drive locations, ie remote mounted in teh field or in a MCC.

We have alway's mounted them in MCC's but they are networked (Devicenet). There appears to be a growing trend towards mounting them in the field and then wiring I/O direct topt he frequency drives.

From an installation poin this makes a lot of sense but from a maintenance point I am not sure.

Any thoughts would be appreciated.

Cheers
Peter

All of our drives are located in the panels at the machines. This makes it easier for troubleshooting/adjustments/resetting/etc.

I have seen them in the MCC at the old plant here in town, but even there majority of the time, they were located in the field.

Our internal standard is becoming that we put them in MCCs.

Over the years, we have done all of the above mentioned options. But with the increasing safety requirements, the easiest way is MCCs.

And alot of our locations are Class II, Div 2 type locations, so our MCC rooms are pressurized, too.

Sometimes, they're individually wired. Sometimes, they're networked (DN or CN). It just depends on the application.

I do a lot of swimming pool jobs. The VSDs are simple devices and are all in IP66 enclosures mounted right alongside the motors in the plant room. Very little very expensive shielded cable to run then. Just send the drive a stop/start signal from the PLC and a 4-20ma signal to adjust speed. Saves heaps on the installation.

I did a bottle line with motor mounted Danfoss FCD's on Devicenet and Allen bradley Point IO for prox's PE.s etc. Worked very well. But plenty of packaging lines still putting in a central MCC / PLC panel. Maintenance wise I saw no issues. In fact, given that a lot bottle line issues relate to PE's dirty/blocked/knocked out of alignment etc, it can be an advantage if the maintenance guy heads out to the line, rather than the MCC. Distributed drives work well when all drives are VSD as you only need CB and safety contactor in MCC and then can daisy chain 3 phase along a VSD zone.

At the Siemens MCC plant, we put larger ones (e.g. 5hp-800hp) in the MCC cabinets.

I don't remember any fractional motor drives installed there.

From a cost effective standpoint, it is probably cheaper to have the inverter as close to the motor as possible.

There is an advantage in having the VFD located close to the motor - reduced harmonics and dV/dt induced stress on the insulation. Another consideration may be the need for local disconnect switches if everything is located in an MCC. Many manufacturers still don't like opening a disconnect while the motor connectied to the VFD is running under load. If this is a concern it tends to favor locally mounted VFDs, whether free standing or mounted in a control panel.

Other than that the trade-offs of local or MCC mounting for smaller drives are the same as those associated with starters mounted locally or in an MCC. Because of the MCC bus-bars for line power I suspect that the MCC installed cost is lower.

Tom Jenkins said:

There is an advantage in having the VFD located close to the motor - reduced harmonics and dV/dt induced stress on the insulation.

Click to expand...

And there is a Max cable length. As an example ABB ACS50 is the max length 75 meters with choke and 50 meters without choke.

Actually, there is no absolute maximum cable length from a technical standpoint. It's just that the cost of cleaning up the motor leads gets impractically expensive.

I suppose you could put a true sine filter on an ACS50 and run the motor leads a half mile but you will have put an $800 filter on a $140 drive. Not exactly a useful thing to do!

Also, some of the really basic small drives don't have very sophisticated ground fault detection systems or any way to turn it off which sets a limit on lead length due to lead capacitance to ground and the resulting leakage current thru it. Installing an expensive sine filter right at the drive output terminals would likely eliminate that problem too but at a cost level which is impractically high.

Full-featured drives will be able to turn off the ground fault protection but you still have to protect the motor from ringing voltages and reflected waves.