Transformer Selection

Mr. Das, As u know the more u get expectation goes up. Thanks for ur contribution but it is not necessary that u should give ur experiences & knowledge. Sorry to say but dont think that the people asking questions are just relying on these answers. Obviously the answers & comments helps a lot. So thanks once again, To all others anybody wants to share knowledge & his experience is most welcome to answer this.

Thanks

Option 2.

3000 kva.

Selection of transformer is an important decision to be taken after considering various technical, financial and administrative aspects. It is the job of a highly experienced Electrical Engineer.Others can give guidance but final decision has to be yours.

Consider the following points they are only vital points.

1. How far is your substation ( Transformers, HT switch gear and LT switch gear and length of cable)from the load and transmission loses.

2. Do you want to go for Dry type transformers or oil cooled transformers. (if your load is close to the substation dry type transformers can be used)

3. Do you want two transformers that can take full load so that in case of failure of one transformer , cable or switch gear, the plant can work on single transformer,( This costs extra financial investment ) partial loading in case of failure ,to run only vital portion of the plant.

4. Two transformers for just minimum capacity. This will cost more money for extra HT and LT breakers and bus couplers in HT and LT.

4. Do you want to plan only for single transformer which is the cheapest proposition.

5. Is there any expansion plan for your work shop or will be fixed load.

6. What is your load pattern, means, weather you have few large motors or many small motors. (Is the load inductive,resistive, or capacitive ) The capacity calculation will depend on that.

7. What will be the peak load and what will be the average load.

8. What is the power factor you want to maintain .

9. Are you planning for APFC ( automatic Power factor corrector or manual power factor correction)

10 How much is your financial Sanction.

11. What is the ambient temperature at your location and what is the temperature rise permitted by the transformer that your want to purchase.

12. The quality of the transformer that you purchase is another important factor

The list is much more . If you can collect all this data you can take your own decision.

I do not want to give you any figurers.

Selection of transformer sizing shall be based on following criteria.

1. Type of connected load, i.e. continuous loads, intermittent loads, stand-by loads etc.

2. type of starter i.e. DOL starter, star-Delta starter, soft starter , VFD .

3. Load factor, Diversity factor , efficiency of the Transformer.

4. Starting current of Highest motor load plus running current of remaining connected motors shall be considered.

5. Design margin shall be consider in addition to all ( say 10-20 %)

6. expected Future load, if any.

7.Duty cycle shall be accounted to get the optimum rating for transformers considering the peak load for shorter duration of time.

Generally,two number of transformers with identical rating shall be considered with 50% loading, which were be operated @ maximum efficiency and also redundancy will be achieved by loading the either transformer with 100 % load,while the other transformer will be under maintenance.

Selection of transformer sizing shall be based on following criteria.

1. Type of connected load, i.e. continuous loads, intermittent loads, stand-by loads etc.

2. type of starter i.e. DOL starter, star-Delta starter, soft starter , VFD .

3. Load factor, Diversity factor , efficiency of the Transformer.

4. Starting current of Highest motor load plus running current of remaining connected motors shall be considered.

5. Design margin shall be consider in addition to all ( say 10-20 %)

6. expected Future load, if any.

7.Duty cycle shall be accounted to get the optimum rating for transformers considering the peak load for shorter duration of time.

Generally,two number of transformers with identical rating shall be considered with 50% loading, which were be operated @ maximum efficiency and also redundancy will be achieved by loading the either transformer with 100 % load,while the other transformer will be under maintenance.

Plants are not stagnant. Whatever load you are planning for... get bigger, double even. The initial investment is cheaper than having to rip everything out and start again. I've seen many plants want to expand and have to spend a lot of money upgrading the basics because they didn't plan for expansion.