How to calculate load on a single phase 480V to 240V/120 transformer

[Todd Lambert]

How is the KVA of a single phase transformer calculated if the load is a mix 240V and 120V circuits? Assume the phases have a balanced load and the loads are either all on or all off.

 

[BAHTAH]

Determine Transformer Size

Determine Transformer Size

How is the KVA of a single phase transformer calculated if the load is a mix 240V and 120V circuits? Assume the phases have a balanced load and the loads are either all on or all off.

100% of the non-continuous load plus 125% of the continuous load. Then add some for future growth based on where this transformer is being installed and what future
expansion may occur. Then in reality the loads will probably not be balanced so I prefer to make a panel schedule and then use the higher loaded phase to help determine
the KVA needed.

 

[kwired]

How is the KVA of a single phase transformer calculated if the load is a mix 240V and 120V circuits? Assume the phases have a balanced load and the loads are either all on or all off.

KVA is still KVA. If both 120 coils are balanced you are ok. You can not load one side to more than half the KVA rating of the transformer. Where there is trouble is if there is unbalanced current and one side should happen to have more than half the KVA rating of the transformer connected to it.

Primary side is going to see all the connected KVA regardless of balancing conditions on the secondary.

 

[charlie b]

How is the KVA of a single phase transformer calculated . . . ?

Add up the currents drawn by all the 240 volt loads, and multiply that number by 240. Add up the currents drawn by all the 120 volt loads, and multiply that number by 120. Add the two values together to get the total KVA on the transformer. Is that what you were asking for?

 

[Todd Lambert]

Thanks for the help

Thanks for the help

"KVA is still KVA" cleared my confusion. I am helping to wire oil processing machinery that is mounted inside trucks .The installation uses a mix of 480V,240V and 110V. Since space ,weight and ,of course, cost are important I needed to check that the single phase transformers used are just right. Thanks for the help.

 

[kwired]

"KVA is still KVA" cleared my confusion. I am helping to wire oil processing machinery that is mounted inside trucks .The installation uses a mix of 480V,240V and 110V. Since space ,weight and ,of course, cost are important I needed to check that the single phase transformers used are just right. Thanks for the help.

You're welcome. Also welcome to the forum. I think you will like the information that bounces around here.