Bm Value in Transformer Design

Well, these things should be in the organisation's design procedures manual, so that is the best place to look.

At the upper limit of rated voltage core should remain well below magnetic saturation.

sreerampkj

Have you ever considered doing your own homework?

If you're going to copy something at least do it in the right order. First you figure out how much power you want transfer through the transformer, then you figure out the size of the conductors for the windings based upon the voltages; when you know the impedance characteristics, then you determine the reluctance of the core to achieve this, THEN you size the core. Otherwise it's like building a vehicle by choosing the tire size first without knowing whether it's going to be a Hummer or a Smart Car...

First, understand what it is. Flux - Wikipedia, the free encyclopedia

Flux density is selected by the following:
Customer's specification for maximum core loss.
Core and or transformer temperature rise must not be excessive.
Transformer maximum inrush current must not be excessive.
Transformer maximum audible noise must meet customer's specification and not be excessive
For some transformers near electronic components, flux leakage may be a problem
For transformers using silicon steel, a good flux density to start a design is 15 kilogauss at 60 hertz, 4 kilogauss at 400 hertz.

You said it right .Only I like to add that distribution transformers are designed with lower flux densities and cosidered value of 1.1 to 1.35 wbs./ sq mt depending up on the core meterial .

Thanks for your valuable answer.

I had one more doubt please clarify this. In vendor catalogue they mentioned

For CRNGO steel -(35H210) = 0.9W/kg@ 1.0T,50hz / 2.1W/kg @1.5T,50Hz

then how I can choose value between 1.1 to 1.35T can you clear this.

Is this standard practice.

My friend was a design engineer he also choosing value between 1.1 to 1.3T, I prepared the same design in excel sheet I had doubt in that design excel sheet can you guide me if I submit that to you.

For Transformer core the type of steel used is CRGO (Coled Rolled Grain Orientated) AND Not CRNGO (Coled Rolled Grain Non-Orientated).

As suggested earlier please get the magnetization curve of 35H210 CRGO from the vendor (I could not find on net) and check point from where the curve tends to be Non-linear. You can maximum increase the designed flux density by 15% above value at this point.

We can not exchange e mail address on this site hence you can not send us the excel file.

If you give me your mail id, so that i can mail my excel sheet to you for that mail id.,

So kindly help me to correct my design excel sheet.

and also can you tell me how to choose the conductor area. Wether this depends upon current density or flux density. if it is depends upon current density means what value i should choose for current density (i.e between J=1 to 3A/mm^2)

Pl advise following:

1. Rating

2. Primary Voltage

3. Secondary Voltage

4. Any preference of vector group.

One of my friend has rewinding shop and carries out rewinding of Large size transformers, 3 phase HT motors and generators. I shall get you data of transformer close to your rating and parameters. That shall give you fare idea of current loading. The Selection of cross section area of Cu, its insulation and clearance between coils is a function of above 4 parameters. Are you a freshers and designing transformer as part of your curriculum (major project)? It is my endeavour to assist Young budding engineers to guide them in the right direction to best of my ability. I am an old man of 65. With Grace of God I have clear concepts in all fields of engineering and from these basics develop the system and won't mind also assisting you.

With flux densities higher than 1.35 wb./sq m the 5th or 7th harmonics become pronounced . For oil cooled transformers 150 to 500 kVA output 1.38 wb /sq m is recommended.For transformers above 500 kVA 1.4 wb./sq m is maximum permissible.

Mr. Abraham,

Sree Ram is coming back on forum with information regarding kVA rating, voltage levels and application of the transformer.

In case you have the date available for kVA rating, voltage levels and application, then please provide him following information:

1. Flux loading for CRGO steel he intends to use.

2. Current loading of primary (considering cylindrical coil)

3. Current loading of secondary windings (for cylindrical as well as disc type coils)

4. Desirable clearance between primary and secondary for the voltage rating.

5. Desirable clearance between cylinders of windings for circulation of cooling oil.

6. Desirable clearance between adjacent discs.

7. Preferable length to dia ratio of coils (Limb) to achieve hotspot temperature within 10°C of average temperature.

8. Details of tapering of insulation of HT coil of line side conductor to absorb surge in case the application is for outdoor transformers of Receiving Station.

To me it appears that Sree Ram is doing h.is Major Project of Third/final year Engineering and needs support of members from CR4 Forum in Design and Manufacturing of transformers

Thanks in anticipation

Dear Abraham & others,

Thanks for giving me those information.As powersolutionFBD said i am a beginer in transformer design.So intially i want to develop in single phase EI type transformer.So guide me for that later you guide me to 150KVA high rated transformer.

Customer Specification for transformer

Rating,pri vt,Sec Vt & eff

From these data i will calculate Pri& sec Ct

but my problem was with calculating core area(i.e stack & tongue width),which EI type to choose,lamination grade,& turns

can u tell listed below formulas are correct for those calculation

1) core area = 1.15*sqrt(rating) (from this core area how can i seperate core width & stack)

2) Pri Turns=(1/(4.44*f*core area*Bm))*pri vt

Please read the following link which gives some basic concept about transformer design

http://ecee.colorado.edu/copec/book/slides/Ch15slides.pdf

http://www.gobookee.org/transformer-design-calculations/