power conversion help please.

[gpu3]

I manufacture vibratory parts feeders and electric is not my bag.

I have a system which I am building in which only 230 3phase power is avalible. My problem is the the feeder drive must run its electro-magnets on single phase power.

I do have a VFD which is running a motor and is capable of single phase output but I will still need pwoer when this shut off plus it will not be running the correct frequency.

anyone got any ideas.

 

[electricpete]

Some ideas:

1 - Use one phase of the three-phase power if you won't overload that phase or cause voltage balance problems for remaining equipment.

2 - Use a Scott or Tee connected transformer to draw one phase power symmetrically from a 3-phase system.

You have the responsibility to make sure it is correct and safe.

 

[electricuwe]

electricpete,

I have to disagree to your statement concerning the Scott ot Tee-connection:

With these connections you will load a three-pahse system symmetrical if the two-phase system at the output is loaded symmetrical. There is no transformer connction to connect a single-phase load to a three-phase-system so that it loads the three-phase system symmetrical.

The classic connection for this purpose is the Steinmetz-Connection (using an additional inductor and capacitor, commonly used for line-frequency induction furnaces).

 

[nbucska]

There is no reason why you can't run the shaker between two
phases : its power is most likely negligeable compared
to other loads, so the assymetry is small.

Using a separate TRA.FO wouldn't be reasonably cost effective.


<nbucska@pcperipherals.com>

 

[electricpete]

Thanks EU. I stand corrected.

 

[gpu3]

Thanks for your help.
The load will be 8amps @220v.

I am kindof concerned about the unbalance issue.
also note my mechanical background so there fore i have know idea what a Scott or Tee connected transformer is.

 

[busbar]

The single-phase 220V motor will equally load two phases of the 230V source. It's hard to comment about the effect of unbalance without knowing more about the source. Is the source particularly “weak” or otherwise susceptible to voltage imbalance?

 

[jbartos]

Suggestion: The VFD output frequency may affect AC electromagnets. It is better to rectify the three phase output from the VFD output by a three-phase full wave rectifier and design your electromagnets for DC. They tend to work better.

 

[gpu3]

The source is suspected to be in good balance already.

The vfd will run a single phase motor but I still need pwoer to my parts feeder when the motor is off.

I will only be reduceing motor speed by 11% if that helps any.

Lets say I hook it up and it does cause an imbalance...what symtoms or problems would you think the vfd may experiance.

The feeder coils will be hooked up prior to the vfd and I do have a controller which will rectify to wave and help compensate for voltage drop. I really don't think low voltage will hurt the feeder coils as long as it is not bad. Will it hurt the VFD?

 

[rlounsbu]

Typical Variable Frequency Drives (VFD) are made up of 3 sections. A rectifier on the input (sounds like a 3-ph rectifier in your case), a DC link, and an inverter that switches the DC to synthisize AC at other frequences and voltages. Voltage imbalance on the 3-phase source may cause additional ripple on the DC link voltage. The DC link usually has large capacitors to keep the DC &quot;smooth&quot;. Ripple will affect the power quality of the VFD output. If you need precise speed and torque controls like a paper mill it can be a problem. For a simple conveyor belt it shoud be no problem at all. Most VFDs will operates with the DC link at any level from 0VDC up to rated... as long as the controls circuits are getting the power they need. For your inital question, imbalance should not be a problem if you are within the KVA rating (per phase) of the transformers supplying your 3-ph source.

 

[busbar]

gpu3 states, “…load will be 8amps @220v” If that is a 1ø load, is there any way it could be done with three ~2.7-amp 1ø devices {&#8710;-connected} to provide a balanced 3ø load?

 

[jbartos]

Suggestion to the original posting gpu3 (Mechanical) Jun 17, 2003 marked ///\\I have a system which I am building in which only 230 3phase power is avalible. My problem is the the feeder drive must run its electro-magnets on single phase power.
///Please, clarify the feeder drive. Is this meant to be the drive output or the feeder of the drive?\\\

I do have a VFD which is running a motor and is capable of single phase output but I will still need pwoer when this shut off
///Will the drive shut off and will you still need power from the shut off drive output?????\\ plus it will not be running the correct frequency.
///Yes, a bigg problem for AC electromagnets.\\

 

[gpu3]

by feeder drive I mean the drive unit for the vibratory parts feeder. It contains my ac electromanets. They must run on 1pahse power and be indepentant of the VFD.

I have figued out that I can get the 1phase power I need off the three phase. but how do a properly fuse this?

My 3phase load will need to be fused at 20A and my single only neds to be fused at 10A.

 

[jbartos]

Suggestion to the previous posting:
The 20A branch circuit may be protected by the 20A or more appropriate fuse, and the 10A branch circuit may be protected by the 10A or more appropriate fuse.
The overall protection is then necessary to increase to protect properly the feeder to both 20A and 10A branch circuits.

 

[jraef]

gpu3,
How big is the motor that's on the VFD? The reason I ask is that if it is small, most small 230V VFDs (3HP and under)can be fed with 1 phase power and they will recreate the 3 phase necessary to run the motor. By doing that and connecting to the leg NOT used by the magnets, you can help to balance your loads.

Just a thought.

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