Transformer Sizing Calculation

If it already exists, then you need to do a survey. Are there any on-site meter readings to help, Captain, and what does the system look like? Nearly all motors have a rating plate on them, which gives its maximum power consumption and may give an idea of the power factor you can expect from it. The lighting loads are going to have a power factor as well, ranging from near-unity for incandescent lighting to something far off for fluorescents. You need to factor in the diversity, which means that not all loads are on at any time. Power factor correction equipment, if present, will help. Meter readings off the transformer will help, but it's a huge pain gathering all the data together.

If it doesn't exist yet, then you need to add up all the design loads and apply a diversity factor. Are you putting power factor correction into the design? Then you need to add a bit more on to allow for future expansion to obtain a preferred transformer size. Then go to the next-one-up at the transformer vendors' literature. Good luck!

You can use this formula:

Transformer Capacity in MVA =

(Total Continuous Load in KW + 60% of Total Intermittent Load in KW + Largest Standby Load in KW + Future Reserve Capacity in KW) / (0.8 x 1000)

- MS

Dear sir

For sizing of the transformer the formula indicated by you is in order.Can you substantiate this by giving some IEC/IEEE reference.

I have a problem with one of my vendors, he is not prepared to accept this.If the same thing indicated in any of the standards I can reproduce then my job will be easier.

Please help.