Power transformer sizing

[power2020]

Dear Folks,
In our project specifications, I have seen the sizing calculations of transformer and is calculated by:
(continuous load X 1 + Intermittent Load X 0.3 + Stand-by Load X 0.1) X factor of safety(1.2)
Anyone pl. explain how to calculate factors for intermittent loads and stand-by loads and if any standards (IEC / IEEE) available, pl. let me know.
Advanced thanks...

 

[wareagle]

I am not familiar with your formula. Explain how you came up with the 1 + Intermittent Load and 0.3 + Stand-by Load X 0.1.
I would estimate as follows:
1.Continuous - 100%
2.Intermittent Load x a diversity factor that you determine.
3.Stand-by Load - I do not understand why this is a separate
load. Is it Continuous or Intermittent?

 

[sslobodan]

You should consider light p. factor 1 because it has small load and it will be all or almost all turned on in same time. Machinery= parallel (work + reserve pump for instance) operation or non parallel. If parallel you take only one in consideration. When you find machinery load you should take p. factor of 0.8 and multiply it because that is usual coefficient of all time operation in facilities. That might not be the truth in all cases so you have to know what is the purpose of facility you are producing (I am talking about small facilities with machinery that turns on and off due to a specific condition). Than you have to see what do you have from large consumers like big pumps. remember that they are usually asking 6x more inrush current than operating one and that they can crush your system (I just have 70.5 A pump behind 1KA transformer and I need to get best solution for letting such pump in operation because it will crush system if there is load and considering it works in parallel operation 12h/12h with one the same like she) and find what is maximum single time inrush current that might happen when such large consumer(s) start and you take that in consideration when setting the maximum power of transformer. When you have all the data, chose first over, what you have heard about 1.2 is a factor that dry transformer can withstand current of 1.2 nominal in permanent operation if the proper cooling is installed. That will be your inrush reserve for everything you haven't calculated (and I still cant calculate all loads inrush current expectation correctly all the time)

 

[power2020]

Stand-by load means redundancy like (one is unit is operating and other is stand-by). so what factor we need to consider for stand-by loads.
Thank you,