imbalanced transformer loading

[Designer69]

I have a 30kVA dry type 3ph 480-120/208 transformer that is loaded 9kva phase A, 9.5kva phase B and 4kva phase C.

obviously very imbalanced.

However, the situation is such that loading of phase A needs to increase a bit to 10KVA.

this will load up phase A to 100% connected load.

My question is.. Will phase A and B in actuality be loaded to more than 100% due to the large load imbalance?

Ps. reason we have to connect to phase A instead of C is because only one space is available, ckt 26, which corresponds to phase A.

 

[Smart $]

10kVA is fine on A (assuming OCPD and wiring are also rated for it), but I don't understand why you are asking about B phase. They only reason I can fathom is if you are adding a L-L or 3Ø load???

PS: Have you considered swapping some circuit-phase pairings?

 

[Designer69]

10kVA is fine on A (assuming OCPD and wiring are also rated for it), but I don't understand why you are asking about B phase. They only reason I can fathom is if you are adding a L-L or 3Ø load???

PS: Have you considered swapping some circuit-phase pairings?

thank you for your help. I only mention phase B so you can see the loading breakdown between the 3 different phases. I am not sure if, in actuality, Phases A & B will draw more than 10kva and 9.5kva respectively, since they are so imbalanced with phase C.

also, I am not sure what "swapping some circuit-phase pairings" is. would you mind a quick explanation?

thanks!

 

[Smart $]

...

also, I am not sure what "swapping some circuit-phase pairings" is. would you mind a quick explanation?

thanks!

Take some A- and B-connected loads and connect to C or better distribute as AC, BC, less AB. Nothing you can do about 3Ø loads.

 

[Smart $]

thank you for your help. I only mention phase B so you can see the loading breakdown between the 3 different phases. I am not sure if, in actuality, Phases A & B will draw more than 10kva and 9.5kva respectively, since they are so imbalanced with phase C.

You'd have to supply a lot more information for anyone on this end to make that determination.

 

[Designer69]

I have attached a pic of the panel schedule. hopefully it helps.

essentially what it amounts to is:
9.7kw ph A
11kw pha B
6.6kw ph C

I am trying to find justification for loading phase B over 10kW. Also, since the loading is relatively imbalanced, realistically, will more than 9.7kw and 11kw be drawn from phases A & B?

any additional info, I'll be happy to provide

 

[Smart $]

Panel schedule too small, too low resolution to make out distinctly, but I can make out that most loads are line to neutral. With the number of circuits, it should not be too difficult to better balance the loads.

It is not advisable to exceed 10kVA per winding, but the transformer [itself] will be able to handle short term low-level overloads... and that'll depend on loads being concurrent. Doing so will decrease the useful life of the transformer.

 

[Sahib]

View attachment 14727

I have attached a pic of the panel schedule. hopefully it helps.

essentially what it amounts to is:
9.7kw ph A
11kw pha B
6.6kw ph C

I am trying to find justification for loading phase B over 10kW. Also, since the loading is relatively imbalanced, realistically, will more than 9.7kw and 11kw be drawn from phases A & B?

any additional info, I'll be happy to provide

Operating a transformer with unbalanced loads within its rating would not harm it, but a 3phase motor load would be seriously harmed.

 

[gadfly56]

thank you for your help. I only mention phase B so you can see the loading breakdown between the 3 different phases. I am not sure if, in actuality, Phases A & B will draw more than 10kva and 9.5kva respectively, since they are so imbalanced with phase C.

also, I am not sure what "swapping some circuit-phase pairings" is. would you mind a quick explanation?

thanks!

If you swapped the loads in CB's 16 & 18, for example, you'd transfer net of 900 watts of load from phase "B" to phase "C". Assuming of course that I'm reading them correctly as 1,100 and 200 watts, respectively. Image resolution is not great.

 

[kwired]

Peak demand and duration might need consideration as well. Just having several loads connected doesn't mean they all run at same time or for very long duration at high demand levels. More load/usage details is necessary to go any further down this path though.

 

[gadfly56]

Peak demand and duration might need consideration as well. Just having several loads connected doesn't mean they all run at same time or for very long duration at high demand levels. More load/usage details is necessary to go any further down this path though.

That's certainly a good point.