600V vs 4160V Motors

[X49]

I'm at the conceptual stage of a facility design where we plan on using two 700-800hp pumps on VFD's. They may run simultaneously and we will have a standby genset. Cable lengths are relatively short. Building loads will be 50-75kVA. A 600V service would be in the 1600-2000A range (provided by the local utility).

My initial thoughts are that 600V will be more economical, but will not allow much room for additional loads/larger pumps. 600V motors don't seem to come in standard sizes above 800hp. MV drives are more expensive, but tend to be IEEE 519 compliant without adding filtering.

I am not very experienced with medium voltage and would be interested in some opinions.

 

[dpc]

Sounds like 600 V would make more sense, unless there is a good possibility of a lot of additional load being added.

Selecting a voltage level requires looking at the entire system, planned growth, as well as any existing electrical systems. You can't just look at one motor especially in this size range.

800 hp VFD can be done at 600 V - but allow a lot of space.



David Castor

http://www.cvoes.com

 

[ScottyUK]

Agree with dpc - LV variable speed drives will probably cause less heartache in the long term, although if it was a staight DOL motor I would have suggested going to MV if you have the technical staff to deal with them - maintenance, switching, etc.

Your generator may be problematic with such a large proportion of VFD load - consider putting either a 12-pulse rectifier or an active front end on the drive to keep the harmonics down, otherwise you are going to be in the market for a big set or a couple of medium-sized sets.


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If we learn from our mistakes I'm getting a great education!

 

[X49]

Thanks for confirming my gut feeling guys.

As for the VFD's causing problems with the genset, the utility requires IEEE 519 compliance so I will likely either go with 18-pulse drives, or the more cost effective 6-pulse drive/passive harmonic filter setup. I'll just have to be careful to make sure the filters are compatible with the genset.

 

[davidbeach]

IEEE 519 compliance while connected to a nice stiff utility system may not tell you anything about what it looks like on standby generators.

 

[purplepete]

I would check the efficiency of the passive harmonic filters. They will generate heat and the active filter may be more cost-effective. Sorry I haven't got the numbers but at that size they could be significant over whatever years lifespan.