Why only "even" number of Generating Units in Power Station? 6

[starwhizz]

So far, I have seen mostly odd number of Units in Hydro Power stations. Why does the designer choose only "even" number of units?? What is the disadvantage of having "odd" number of units??

I would appreciate some answers.

Thanks

 

[Skogsgurra]

The heading says only even numbers.
You then say that you see mostly odd numbers, followed by an assumption that designers chose even numbers.

Not easy to understand what you actually mean. But interesting question.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Arevaengineer]

The only reason I can think of is to have a balance supply on the bus that they are feeding.

 

[waross]

Well our little island plant ran for years with five generators. Those five are no longer in service. They have been replaced by two much larger sets. We experienced no numerological effects going from five to two.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Bill

I remember now that there was a little creek over here where eleven little hydro stations delivered just under 1 MW. They have now been replaced with one unit. So, I think that odd numbers actually are better than even numbers. And prime numbers like 11 and 1 seem to be very good.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Well our operating plan is N+1 so we actually have 1 and 1 rather than 2. I hope that I haven't mislead anyone with incomplete information in my previous post.
Can we safely say that "Odd" numbers feel better? Have I missed the point again. Should I have said that prime numbers feel better. Except 13, Don't use 13 sets on Fridays.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rcw retired EE]

Combined cycle plants have a combustion turbine generator and a steam turbine generator. The steam comes from a waste heat recovery steam generator (HRSG). Many plants use a 1 on 1 configuration with one CTG feeding one STG. Multiple units are built in identical 1-on-1 blocks so each block has two generators. (Rule of thumb: STG MVA = 50% of CTG MVA). Even numbers of generators result.

Many plants use two-on-one designs with two CTG's supplying steam to one STG, so each block has three generators each of about the same size. Then you get odd numbers.

Odd or even may make a difference. If we are worried about it, should we count the blackstart and emergency generators too?

 

[electricpete]

Many plants use two-on-one designs with two CTG's supplying steam to one STG, so each block has three generators each of about the same size. Then you get odd numbers.

I think you mean odd or even.

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[mgtrp]

Here's my experience:
First employer's power stations had:
Hydro: 3 units, 4 units, 4 units, 4 units, 5 units, 5 units, 3 units, 8 units, 3 units; Combined cycle: 4 units; Geothermal: 5 units, 5 units, 3 or 5 units (I forget), 1 unit; and some other very small methane-powered sites that I've forgotten, but they were about 4-5 units each.

Second employer:
Hydro: 2 units, 5 units, 2 units

Current employer:
Hydro: 3 units, 3 units, 1 unit, 2 units, 2 units
Diesel: 7 units, 4 units, 4 units,

So I see no real pattern in terms of number of generators at the places that I've worked at.

 

[marks1080]

even or odd number of units has no meaning at all...

 

[tinfoil]

My 'theory':

first engineer designs with even number because the plans look more symmetrical and therefore 'feel better'.

At some future time, someone figures out that they can 'squeeze' in a bit more capacity and adds one more: odd final number

Besides, it's better feng shui.

 

[electricpete]

Here is a list of US nuke sites.

http://www.nrc.gov/reactors/operating/list-power-reactor-units.html

You can scan the list and see the number of onezies, twozies, and threezies.

I haven't done any statistical analysis on those numbers (and don't intend to!), but I don't see any pattern.

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[vtb1]

I have seen even and odd numbers for both hydro and thermal power plant. So my opinion is there no any logic behind to choose even or odd number of stations.

 

[Skogsgurra]

Next question: Is the number of employees even or odd? Pls note that zero counts as even.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[burnt2x]

Does the adage "two of everything" have anything to do with "even" choices? - (redundancy)

 

[marks1080]

It's a question of economics and nothing else. Different types of plants (hydro, fossil, nuclear) have different methods of determining this. If hydro, for example, you know the max amount of power your water system can provide. Then you look for the cheapest way of turning that power into MWs. Sometimes you buy an even number of units, sometimes and odd. It's nothing more than that.

The nuke site I work on has two plants, with four units each. Each unit is rated at about 900MW. There is a lot of consideration given to building a new plant on site. I know that if they do it will be only two units, with each unit rated about 1600 MW. Why? Because they can build this now. When the first two plants were built it was too expensive.

The only thing you will not ever see (unless its a very small installation) is a plant with one unit. Can it be done? Yes. But what about outage situations? You lose all of your revenue for any outage.

 

[rmw]

Forget the little one unit Peaker stations, what about Gerald Andrus SES, Greenville, MS? One unit, ~800 MW?

What about Grand Gulf, Port Gibson, Miss, Nuclear, 1300 MW? (although in all fairness, it was to have been 2 units, the second was sold for scrap instead of constructed.)

What about SWEPCO Gentry, Ar? One unit, ~550 MW. (although in fairness, it was to have been a 2 unit station, but the utility got fed up with the state regulators and moved the second unit to become unit 3 at their Welsh Station.)

What about Swepco Pirkey plant, lignite 8-900 MW, Lignite?

What about Cleco Dolet HIlls, lignite, 8-900 MW, Lignite, both one unit stations.

What about MP&L Natchez (now retired) one unit, ~60 MW - large station in the day it was built.

What about Oklaunion near Vernon, TX? (I can't remember if it is West Texas Utilities or who.) One unit in the 900 MW range.

I think if I kept thinking, I could come up with many more single unit stations of significant size. So, Marks, I don't think your last statement is accurate.

rmw

rmw

 

[edison123]

What's odd is this post is being taken seriously at all especially given that the OP mangled his own post.

Muthu

http://www.edison.co.in

 

[waross]

I think that Gunnar may be on to something with his suggestion that prime numbers are good.
Looking through mgtrp's star studded post, it seems that although not all the stations that he lists have an odd number of sets, the ones that do have odd numbers all have prime numbers.
Seriously, it must be a slow day, Muthu.
Next question: Why are some plants 50 Hz and others are 60 Hz??



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

We could have some fun with this Bill finally.

Why are some machines dc and others ac ?

(Do I get a lps for that ?)

Muthu

http://www.edison.co.in