Transformer calculation

[shortcircuit1]

Hello,

If i have a 3phase 480-208v 75kva step down transformer supplying a panel 208v,3phase which carries a load of 100kva. How do you relate that kVA to 480v side or what kva would it be on 480v side?

Thanks,
shortcircuit.

 

[jumper]

Same kVA for both sides.

 

[Jraef]

Hello,

If i have a 3phase 480-208v 75kva step down transformer supplying a panel 208v,3phase which carries a load of 100kva. How do you relate that kVA to 480v side or what kva would it be on 480v side?

Thanks,
shortcircuit.

Well if your load is TRULY 100kVA in the load side of a 75kVA transformer, you are missing the elephant in the room...

But to your question, kVA is kVA. It doesn’t change with voltage, that’s why you use that instead of amps.

 

[jumper]

Well if your load is TRULY 100kVA in the load side of a 75kVA transformer, you are missing the elephant in the room....

I know I missed it...:slaphead:

 

[charlie b]

. . . supplying a panel 208v, 3 phase which carries a load of 100kva.

Is that 100 KVA a connected load or a calculated demand load?

 

[jumper]

Is that 100 KVA a connected load or a calculated demand load?

Why would it matter?

Are you thinking a calculated load could be too high?

 

[Besoeker]

Is that 100 KVA a connected load or a calculated demand load?

Are you thinking of a diversity factor?

 

[jumper]

Are you thinking of a diversity factor?

Not fair, that is something the NEC only allows EEs to consider!

 

[charlie b]

Why would it matter? Are you thinking a calculated load could be too high?

The total connected load might be 100 KVA. But some of that may be non-coincidental loads, and there may be demand factors that come into play. So the total demand load might be lower than the transformer's 75 KVA rating. If so, then there is no problem with using a 75 KVA transformer for this application.

 

[jumper]

The total connected load might be 100 KVA. But some of that may be non-coincidental loads, and there may be demand factors that come into play. So the total demand load might be lower than the transformer's 75 KVA rating. If so, then there is no problem with using a 75 KVA transformer for this application.

Okay cool, that I understand. I was thinking something else.

 

[shortcircuit1]

The total connected load might be 100 KVA. But some of that may be non-coincidental loads, and there may be demand factors that come into play. So the total demand load might be lower than the transformer's 75 KVA rating. If so, then there is no problem with using a 75 KVA transformer for this application.

My bad i picked a poor example.

 

[Besoeker]

The total connected load might be 100 KVA. But some of that may be non-coincidental loads, and there may be demand factors that come into play. So the total demand load might be lower than the transformer's 75 KVA rating. If so, then there is no problem with using a 75 KVA transformer for this application.

I was thinking maybe some of the loads don't run continuously and/or at lower than their nameplate rating.
Not enough information. It needs a detailed study.

 

[jumper]

I was thinking maybe some of the loads don't run continuously and/or at lower than their nameplate rating.
Not enough information. It needs a detailed study.

Sparkies always have to go by nameplate...

 

[Besoeker]

Sparkies always have to go by nameplate...

I would always advocate that for cabling individual pieces of equipment.
But adding together the total name of all the nameplate to come up with required supply capacity could be overkill in some cases.

 

[jumper]

I would always advocate that for cabling individual pieces of equipment.
But adding together the total name of all the nameplate to come up with required supply capacity could be overkill in some cases.

I totally agree, but unless you are an EE or a major EC they get nervous when us little guys start doing that.

 

[Besoeker]

I totally agree, but unless you are an EE or a major EC they get nervous when us little guys start doing that.

Yes, I can see that. I've come across the whole spectrum of electricians in my field.

 

[kingpb]

Not fair, that is something the NEC only allows EEs to consider!

Utilities are notorious characters for this when sizing transformers.

 

[electrofelon]

They have current transformers, and potential transformers....if only someone would invent a KVA transformer

 

[topgone]

Utilities are notorious characters for this when sizing transformers.

Nah. That's not true. It just that utilities factor in the life of the transformer as compared to investing on a bigger transformer when the smaller could do the job at the edge of the limits.