Thank you for your reply, Sir.

I would like to clarify that I am specifically asking about the Power Transformer – 30 MVA, 66 kV HV / 33 kV LV.

The basic parameters/specifications I am considering are:

1. Transformer Rating: 30 MVA, 66 kV HV / 33 kV LV
2. Application: Power transformer for transferring power from the generating station to the load end, including step-up and step-down applications.
3. Cooling: ONAN – Oil Natural Air Natural
4. Winding: 2-Winding – HV and LV
5. Tap Changer: OCTC
6. Percentage Impedance: Z = 10%
7. Total Losses: Approximately 0.9% (No-load loss + Load loss)
8. Vector Group: Dyn11
9. Conductor: Copper winding, with a current density of approximately 3.2 A/mm²
10. Maximum Flux Density: Approximately 1.69 Tesla
11. Winding Construction:

- LV – Helical/Spiral winding
- HV – Disc/Layer winding

Based on the above input parameters, I am looking to develop an Excel-based technical transformer design calculation sheet that can automatically calculate/generate the following:

1. Number of turns/steps and voltage per step
2. Complete HV and LV winding specifications
3. Core design parameters
4. Radiator/cooling system specifications
5. Transformer tank dimensions – L × W × H, including required thicknesses
6. Weight calculations – Core & Active Parts (CA), Copper/Conductor & Active Parts (CCA), tank and total transformer weight
7. Guaranteed no-load and load losses
8. Electrical and routine/type testing details
9. Special BOM (Bill of Materials)
10. Manufacturing drawings and required design dimensions

My objective is to develop a practical technical design Excel sheet for a 30 MVA, 66/33 kV power transformer, where the main input parameters are entered initially and the sheet calculates the major electrical, mechanical, thermal and manufacturing design parameters accordingly.

I would appreciate your guidance on the design methodology, calculation formulas, and Excel structure required to develop this transformer design sheet.

 

While not a spreadsheet, I can recommend an excellent book that covers the design of all basic types of magnetic components. It is written not as a 'top-level' answer book, but more of a fundamental, no nonsense book that takes you to a surprisingly high level of understanding for various types of magnetics. It should be a good aide if you have to develop your own spreadsheet.

Magnetic Components: Design and Applications
Steve Smith
ISBN: 0-442-20397-7
Van Nostrand Reinhold Company, Inc

Chapter headings are
1) Low Frequency Power Transformers
2) Optimization
3) Power Reactors
4) Nonlinear Magnetics
5) Current Transformers
6) Pulse Transformers
7) Field Gradient Control
8) Heat Transfer
9) Materials and Fabrication Methods

 

I think winding all 3 windings on a single toroid would work. That way the magnetic flux from each winding would be contained within the core and be able to cut the turns of each individual winding. Of course the core would have to be sized to handle the maximum flux. The windings could be wired Y or delta.
View attachment 370901

Unfortunately not. Toroids couple flux very well, and all you would be doing is connecting the phases together.
EI three-phase transformers have bobbins on each leg, so that the flux in the I sums to zero.

 

Unfortunately not. Toroids couple flux very well, and all you would be doing is connecting the phases together.
EI three-phase transformers have bobbins on each leg, so that the flux in the I sums to zero.

Very well noted.
That would end up in a short circuit in the transformer.

 

Thank you for your reply, Sir.

I would like to clarify that I am specifically asking about the Power Transformer – 30 MVA, 66 kV HV / 33 kV LV.

The basic parameters/specifications I am considering are:

1. Transformer Rating: 30 MVA, 66 kV HV / 33 kV LV
2. Application: Power transformer for transferring power from the generating station to the load end, including step-up and step-down applications.
3. Cooling: ONAN – Oil Natural Air Natural
4. Winding: 2-Winding – HV and LV
5. Tap Changer: OCTC
6. Percentage Impedance: Z = 10%
7. Total Losses: Approximately 0.9% (No-load loss + Load loss)
8. Vector Group: Dyn11
9. Conductor: Copper winding, with a current density of approximately 3.2 A/mm²
10. Maximum Flux Density: Approximately 1.69 Tesla
11. Winding Construction:

- LV – Helical/Spiral winding
- HV – Disc/Layer winding

Based on the above input parameters, I am looking to develop an Excel-based technical transformer design calculation sheet that can automatically calculate/generate the following:

1. Number of turns/steps and voltage per step
2. Complete HV and LV winding specifications
3. Core design parameters
4. Radiator/cooling system specifications
5. Transformer tank dimensions – L × W × H, including required thicknesses
6. Weight calculations – Core & Active Parts (CA), Copper/Conductor & Active Parts (CCA), tank and total transformer weight
7. Guaranteed no-load and load losses
8. Electrical and routine/type testing details
9. Special BOM (Bill of Materials)
10. Manufacturing drawings and required design dimensions

My objective is to develop a practical technical design Excel sheet for a 30 MVA, 66/33 kV power transformer, where the main input parameters are entered initially and the sheet calculates the major electrical, mechanical, thermal and manufacturing design parameters accordingly.

I would appreciate your guidance on the design methodology, calculation formulas, and Excel structure required to develop this transformer design sheet.

Just one thing that I take out for pointing, and it will change a lot the design: isolating that high voltage.
Then you design to not to burn everything in a short-circuit for a X amount of time, and that all change.
It's VERY complex and non-intuitive how one would calculate such things, because the implications are not easy to capture a function.
I think that this kind of project is much more starting from the isolation, power dissipation, losses in the core, losses in the copper, and some iterations to see how it affects power dissipation, maybe. Maybe all it matters is the short-circuit current for X seconds.
I feel that it's all belonged to the industry that does these things by empiric data and feeling, rather than calculating a long spreadsheet.

 

I think winding all 3 windings on a single toroid would work. That way the magnetic flux from each winding would be contained within the core and be able to cut the turns of each individual winding. Of course the core would have to be sized to handle the maximum flux. The windings could be wired Y or delta.
View attachment 370901

if all secondary windings are on the same toroidal core, how would you get different phases? they all would be subjected to same flux....

 

Generally, the best plan is to let someone else do the heavy-lifting and calculations as described in my Post #10 from 3-years ago.

The picture provided in Post #18 WILL NOT WORK under any circumstances,
ALL WINDINGS WILL BE SHORTED TOGETHER.

You will need 3-separate Cores for 3-Phase Power, there are NO exceptions.
Please see Post-#10 from this thread 3-years ago.

 

Thanks all for correcting me. I guess I was thinking the 3 phases would combine in the windings. A little while after posting the drawing it started to look like just a single phase transformer with two secondaries. I should read "Magnetic Components" again.