Generator Sizing 1

[hanksmith]

As a part of a project I am working on I have to size a generator.

The generator will be used as a standby power source, used only when utility goes down.

The primary function of this generator is to power a mine hoist to get men out of a mine. Secondary functions include dewatering pumps, site heaters, site emergency lights, comms, and various other minor loads.

The hoist motor is synchronous and currently sized at 5.5MW (7000hp) and when power is down the hoist will be run at half speed, the reason for doing this as I understand is to reduce the size of the required generator. The hoist motor is controlled via a ABB ACS6000 drive or equivalent.

My plan on sizing this generator;
- ensure that hoist operates in the capability curve of the generator
- ensure that generator is stable for the entire hoisting cycle
- If generator is within the capability curve and stable for entire hoisting cycle all other loads should have no issues - my thought on this one is the generator will have to be oversized for the hoist and the other loads will fit within this oversized portion.

Does this look correct?
Is there anything else I should be looking at?
Does anyone know of a good paper or other sources of information on sizing of generators for applications similar to this?

Thanks

 

[rbulsara]

Depends on what the other loads are.

My view is that it does not cost that much more to invest in a larger generator and have some margin. I would not skimp on generator sizing. Especially if availability of the hoist can keep the business running (revenue) during an outage.

Rafiq Bulsara

http://www.srengineersct.com

 

[wolf39]

You better ask a professional consultant to do the planning.

Regards

Wolf

 

[rbulsara]

Amen to wolf39's post!

Rafiq Bulsara

http://www.srengineersct.com

 

[hanksmith]

The sum of all other loads is small compaired to the hoist load.

The Client does not plan on operating on standby power, only to get the men out of the mine, therefore no revenue.

I am employed by the consulting firm, and yes I will have to get someone involved who knows more then me on generator sizing, we have the experts within the company, but by passing it off completly I will never better myself, hence the reason for looking into this.

If more specifics are required let me know and I will provide more,

Thanks again

 

[rbulsara]

You will learn a lot more while working with experts within your company. I personally don't feel like spending time, while your company is getting paid for the work.

Rafiq Bulsara

http://www.srengineersct.com

 

[edison123]

Rafiq - a lps.

To OP - This is mainly a trouble shooting forum for engineers with real work related problems, not a free on-line consultancy service.

Muthu

http://www.edison.co.in

 

[catserveng]

I think you really should consider a consultant as Rafiq said. At 5.5MW you are in the realm of a medium speed unit if you want a single engine generator. If you need fast start and good transient response that is probably not your best choice. So that leaves a multi unit high speed engine system with paralleling switchgear. Not an uncommon solution, but will require an experienced evaluation of your site and desired emergency operation, and applicable regulatory requirements.

 

[ScottyUK]

Couple of things to look at:

- Governor loop performance. Most big drives have a fairly tight tolerance on the acceptable supply frequency range.
- Synchronous drives can normally regenerate into the source. Engines hate being driven as compressors.


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

 

[davidbeach]

Scotty has pointed out the biggest fly in the ointment, any regeneration by the hoist (and they would usually regenerate one direction or the other) and you have to have something that can absorb the power instantaneously. In other words, you need to have more other load on the system at all times than the maximum regenerated power. This could even include load banks.

 

[chimse]

i think sizing is not the issue,if you are working with experts in your firm why not consult to them,the other is that when procuring a genset consider mostly the load at which it will be operated so in this case go for the KVA rating,add your load and the total will teel you the size of the genset you will require

 

[hanksmith]

Thanks,

I agree, the more I look into this problem the less I see sizing the generator as an issue.

For sizing I am going to plot the capability curve of the generator and compair it to the power locus of the hoist.

I think the problem I am going to run into is going to be the stability of the generator. I have been told that a rule of thumb for generator step loading is about 40% of the generator load.

If this is the case the generator would have to be oversized to remain stable when the hoist is started. Something I will have to investigate to educate myself.