×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

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

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

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

(OP)
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

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

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

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

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

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

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 They have been replaced by two much larger sets.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

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

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

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

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

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

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?
 

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

Quote:

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.   

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

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

2
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.

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

2
even or odd number of units has no meaning at all...

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

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.

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

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.  

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

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

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.

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

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

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

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

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

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

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.

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

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

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

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

Muthu
www.edison.co.in

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

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

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

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
www.edison.co.in

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

how about why horizonal CCW rotating units should be aligned e-w, where CW units are w-e, except if aligned n-s, which should be avoided if possible (applicable to northern hemisphere) :)

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

Years ago, a numerologist on the crew unintentionally entertained us. I wonder what the numerologically optimum number of sets would be.
As for AC versus DC, I guess that it depends on your personality. DC is steady and dependable but most designers seem to want more excitement and go for the peaks and valleys of AC.
(I'm starting to enjoy the new medication.)  

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

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

Should verticle sets rotate with the earth's direction of rotation or in opposition to the earth's rotation? May there be adverse long term affects to the inclination of the earth's axis if the net rotating mass becomes too great in either direction?
Enquiring minds want to know!!

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

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

I must say that, given all the possible combinations, it is a miracle that we have power stations at all! How could the designers make up their minds? And we have not even started to consider things like colour of the machinery.

It boggles the mind.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

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

I still have the color pattern selection page from one of my first power plant start-ups.  The lead engineer couldn't decide on the colors so he told his wife to pick them.  She cut color blocks from a magazine and pasted them to a sheet of paper, and lo and behold, the gas turbine was one color, the steam turbine another, the generator yet another and the (axial flow above grade condenser) was deep blue.

It was an odd assortment of colors, and somewhat feminine, I thought, soft pastels except for the deep blue condenser, but that is what she picked, and what we painted them.

Now, when it comes to E-W vs N-S, I have observed unscientifically over a long period of time that N-S oriented solid fuel boilers with wear particles in the flue gasses have heavier wear weighted to the west side of the parts of the units subject to wear where E-W oriented units have essentially even wear.  Coriolis effect????  Make up your own mind.  A very small percentage of a lot of particles thrown to the Coriolis reaction side of the gas passes could add up.

http://en.wikipedia.org/wiki/Coriolis_effect

I can't say whether or not that is the case, but I do know that if I ever had to site my own unit, I know which direction it would face.

rmw

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

Look all around you:
2 hands, 2 feet, 2 eyes
male occurs with female = gettting even
negative occurs with positive = 2  or 0, all is well whichever way you take it
Guess the universe is in harmony only when everything works out even
see, good and evil = 0, in nothingness is calm!  

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

Quote (darai):


Look all around you:
2 hands, 2 feet, 2 eyes
male occurs with female = getting even
negative occurs with positive = 2  or 0, all is well whichever way you take it
Guess the universe is in harmony only when everything works out even
see, good and evil = 0, in nothingness is calm!  
Darai, dichotomizing sometimes simplifies things, but I think it's not even close to the realities!
Flexibility requirement is and always will be the main criterion for any plant designer. As posted by others, the "what if" one unit conks out?, demand rises above the capacity of one unit?, etc. . will have to be answered by the decision-makers!
Having said that, it's not only the number of units that comes into the equation but also the size of each unit, the expected demand at different times of the day, as well as the seasonal demand profile of the load served. Still, the bottom line will be how deep the pockets of the proponents have.
Respectfully.

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

Thank you everyone! I am sorry about the mess up between "odd" and "even". I tried to log in to edit the post, but i was not able to log in as "starwhizz". I always face problem with log in!

I got my answers. And I am glad my Q provided some amusement to you all.  

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

I had a look at your stats. It appears that this was your first posting in Eng-Tips. Please come back with more 'interesting' questions. We (at least me) liked this.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

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

darai,
how about a tongue, a forehead, a nose, a brain. Last time I checked I only had one of each! :)
 

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

Oh by the way, being one of the chemical folks I figured you would know a thing or two about entropy. :)

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

Some visitors here only have three of the four components you listed... smile
  

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources