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Anonymous Poster #1

Generator for LV MCC

12/16/2012 5:46 PM

Hello All,

How feasible is a generator usuage for running 3 45kW VSD controlled motors and some other loads? Total load will be about 250 Amps @ 415V, 3 phase.

Any thoughts would be appreciated.

Thanks

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#1

Re: Generator for LV MCC

12/16/2012 6:10 PM

Feasible yes, what you are probably after is a 150kW diesel generator or larger (you don't mention the size of "the other loads").

Example Link with Pricing

Plenty more available on the internet, and they can go up to about 2000kW (40 foot container size) before they start go get really specialised and expensive.

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#3
In reply to #1

Re: Generator for LV MCC

12/16/2012 6:26 PM

Thanks for the reply,

I forgot to mention that this is not a back up generator and no mains will be available and the motors will be in Hazardous Area. This generator will be a standalone source of supply.

The total load is about 250 Amps. which includes heat tracing, instruments, etc..

Do you think there will any technical hindrances implementing this solution? On paper it looks good though.

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#4
In reply to #3

Re: Generator for LV MCC

12/16/2012 6:52 PM

Motors are obtainable for usage in hazardous locations, and they don't care too much about the source of power. Hazardous location generators are less likely to be available, and therefore may need to be segregated by walls and/or distance, with sealed conduits to the motors. Please study and conform to local regulations.

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#5
In reply to #3

Re: Generator for LV MCC

12/16/2012 7:14 PM

That's all fine (in general) as long as the generator and variable speed drives are located in the safe area outside the hazardous area zone(s) and that the motors are hazardous area-rated motors and installed as per the relevant hazardous area standards.

Variable speed drives are difficult and/or expensive to install in Ex d (or possibly Ex p) enclosures due to dissipated heat (especially for Ex p, which is only included as an option). You really don't want to install them in the hazardous area unless you really have to, the same goes for the industrial gen-set.

What country is the site in? You should contact your local hazardous are supplier for more information and a quote for hazardous area solutions that meet your requirements (R Stahl US or Europe spring to mind).

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#9
In reply to #5

Re: Generator for LV MCC

12/17/2012 3:16 AM

It is unwise to install a drive in an Ex p enclosure, as it will prove impossible to modify drive parameters without de-energising the drive and parameter keypad first.

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#10
In reply to #9

Re: Generator for LV MCC

12/17/2012 2:13 PM

Ex d enclosures also suffer from the same problem of parameter modification (both require a hot work permit or similar to open and change when installed in the hazardous Zone).

That's not actually the biggest problem thou. The biggest problem is that the maximum heat dissipation limits of Ex p enclosures are quite small when compared to Ex d enclosures and hence you would require absolutely massive Ex p panel unless the drive had external heat sinks that could be passed out through the back of the Ex p panel wall (and properly sealed), and even then the panel would still have top be large to handle the internal drive heat dissipation.

Ex p was only included as a theoretical possibility for comparison, it is not viable for this application in practice.

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#13
In reply to #3

Re: Generator for LV MCC

01/16/2025 6:07 AM

<...technical hindrances...>

  1. Clearly the <...generator...> needs to be located outside the <...Hazardous Area...>.
  2. The installation must be designed, selected, installed and tested by personnel having had specific training for the use of Electrical Equipment in Hazardous Atmospheres.
  3. Consult a qualified Electrical Engineer to carry out the design and look for training pack evidence as part of that individual's documentation.
  4. Consult a qualified local Electrician and look for training pack evidence as part of that individual's documentation.
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#2

Re: Generator for LV MCC

12/16/2012 6:12 PM

A 225 to 250 kW generator should be about right for this.

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#6
In reply to #2

Re: Generator for LV MCC

12/17/2012 12:11 AM

I think it is on higher side .If you select 225 KW generator, it's full load current will be 390A with 0.8 lag.p.f..With 80% loading it comes to 320A.So i think it would be better to go for 200KW.

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#7
In reply to #6

Re: Generator for LV MCC

12/17/2012 12:23 AM

That too might work. We don't yet know all the other loads besides the (3) 45-kW motors. I allowed for the starting load of the largest motor plus other loads of say 20-30 kW. Using VFDs may also allow for a somewhat smaller genset.

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#8
In reply to #7

Re: Generator for LV MCC

12/17/2012 1:56 AM

yes i agree with you.

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#11

Re: Generator for LV MCC

12/18/2012 3:21 AM

wow, i may know you...

what are you running? what are the loads? are you compelled to design/construct based on calculated loads or can you build/design on measured loads? will all three motors start at the same time?

are the motors in zone 1 or zone 2? is this a permanent installation or temporary? are you running fixed wiring or plug and socket?

does the vsd comply with the motor's certification?

what country are you working in?

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#12

Re: Generator for LV MCC

12/18/2012 9:01 AM

Feasible, but harmonic amplification might increase.

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