500 KVA transformer output

[Geoffhelton]

Hello all,
I'm a residential electrician and I don't have much dealings with large power distribution equipment. I'm trying to get a simple answer but am having a hard time finding one. I have reviewed as many posts as I can find but am not getting one answer but two. I was looking at a 3 phase transformer here in Tanzania and I'm just trying to understand what's being stated. The nameplate rating says it's a 500 KVA transformer it has 400v phase to phase and has 721.6 A. I have found people that state it's 721.6 A total and must be divided by 3 for the output of each phase, yet others say it's 721.6 A each phase.

I have a few questions.
1. Is this 500 KVA total or 500 KVA from each phase?
2. Am I correct that this is 721.6 amps from each phase not 721.6 amps total?
3. If 721.6 amps each phase would I be correct that each phase at max could output 721.6 amps x 400v = 288,640 watts

Thanks all for your help.
I have tried to include a picture of the nameplate for other information I might have missed.

 

[Carultch]

Hello all,
I'm a residential electrician and I don't have much dealings with large power distribution equipment. I'm trying to get a simple answer but am having a hard time finding one. I have reviewed as many posts as I can find but am not getting one answer but two. I was looking at a 3 phase transformer here in Tanzania and I'm just trying to understand what's being stated. The nameplate rating says it's a 500 KVA transformer it has 400v phase to phase and has 721.6 A. I have found people that state it's 721.6 A total and must be divided by 3 for the output of each phase, yet others say it's 721.6 A each phase.

I have a few questions.
1. Is this 500 KVA total or 500 KVA from each phase?
2. Am I correct that this is 721.6 amps from each phase not 721.6 amps total?
3. If 721.6 amps each phase would I be correct that each phase at max could output 721.6 amps x 400v = 288,640 watts

Thanks all for your help.
I have tried to include a picture of the nameplate for other information I might have missed.

1. 500kVA total. It is a combination of 167 kVA individual transformers.
2. 500 kVA at 400V = 721.6A per phase. So each line conductor exiting the unit will carry 721.6A, at 230V line to neutral.
3. No, because you need to account for the three phases. Power = Volts-phase-to-neutral * amps per line conductor * qty of phases. So it is either 230*721.6*3, or 400*721.6*sqrt(3).

 

[jumper]

I have a few questions.

1. Is this 500 KVA total or 500 KVA from each phase?

Total.

2. Am I correct that this is 721.6 amps from each phase not 721.6 amps total?

Although not really correct for simplicity I will say amps per phase, although you cannot add the amps for a total.
We can explain in more detail if you really want the full/true answer.

3. If 721.6 amps each phase would I be correct that each phase at max could output 721.6 amps x 400v = 288,640 watts

721.6 amps x 400v = 288,640VA x 1.732 = 500,000VA or 500kVA.

Use VA not Watts You forgot 1.732, always a factor in 3 phase

 

[Besoeker]

1. 500kVA total. It is a combination of 167 kVA individual transformers.

Or, quite likely, one three-phase transformer.

2. 500 kVA at 400V = 721.6A per phase. So each line conductor exiting the unit will carry 721.6A, at 230V line to neutral.

It's 721.6A. You don't need to qualify it as line to neutral. If you had a balanced 3-phase 400V load the neutral wouldn't come into it.

3. No, because you need to account for the three phases. Power = Volts-phase-to-neutral * amps per line conductor * qty of phases. So it is either 230*721.6*3, or 400*721.6*sqrt(3).

Thats kVA, not power. Important distinction.

 

[Carultch]

Or, quite likely, one three-phase transformer.

It's 721.6A. You don't need to qualify it as line to neutral. If you had a balanced 3-phase 400V load the neutral wouldn't come into it.

Thats kVA, not power. Important distinction.

Maybe I should've specified, individual transformer winding pairs. Usually wired together and enclosed in the same factory assembly we call a three phase transformer.

Indeed it is KVA, and not necessarily power.

I'm trying to explain an intuitive understanding to the VA calculation in three phase. I can see where VA = Vp-n * I * 3 comes in to play immediately, as it is the equivalent of 3 single phase-to-neutral circuits operating at the phase-to-neutral voltage. Due to the respective phase shifts, the current adds up to zero on the neutral, so in some cases it can even be omitted. So that is where VA = Vpn * I * 3 or VA= Vpp*I*sqrt(3) comes from.

 

[iwire]

Can I ask the members here to stay on the OPs topic and not get side tracked with your own agendas.

 

[Geoffhelton]

still a little unclear

still a little unclear

Thanks everyone for your input!
So I'm hearing that it's 500 KVA total, and that each phase to phase has 400v and 721.6 Amps, but the math I'm seeing isn't adding up to me.
"721.6 amps x 400v = 288,640VA x 1.732 = 500,000VA or 500kVA."
it would seem this is 500 KVA per phase then? If from phase A to phase B I have 400v and 721.6 Amps if I'm then supposed to multiply by 1.732 and get 500KVA, it's looking like taking power from phase A & B will give me 500KVA and likewise B & C and C & A?

If a combination of 3 single phase 163KVA in one box shouldn't the "ab" on the nameplate be listed as 417.5A phase to phase?

I have a report that that the facility consumes a certain amount of KiloWatts, I'm trying to inform the manager what the capacity of the transformer is in the same terms that he is used to, that's why originally I asked for watts(P) not VA.

Thanks everyone again for your help understanding this!

 

[Besoeker]

Thanks everyone for your input!
So I'm hearing that it's 500 KVA total, and that each phase to phase has 400v and 721.6 Amps, but the math I'm seeing isn't adding up to me.
"721.6 amps x 400v = 288,640VA x 1.732 = 500,000VA or 500kVA."
it would seem this is 500 KVA per phase then? If from phase A to phase B I have 400v and 721.6 Amps if I'm then supposed to multiply by 1.732 and get 500KVA, it's looking like taking power from phase A & B will give me 500KVA and likewise B & C and C & A?

If a combination of 3 single phase 163KVA in one box shouldn't the "ab" on the nameplate be listed as 417.5A phase to phase?

First, it is unlikely to be three separate single phase units. One three phase unit rated at 500kVA wound on one common core.

I have a report that that the facility consumes a certain amount of KiloWatts, I'm trying to inform the manager what the capacity of the transformer is in the same terms that he is used to, that's why originally I asked for watts(P) not VA.

With the given kVA and Volts you can calculate, as you have done, the maximum current the transformer can provide. It's how thw loads use that current that determines the watts.
More later......the dog you understand..............

 

[Besoeker]

I have a report that that the facility consumes a certain amount of KiloWatts, I'm trying to inform the manager what the capacity of the transformer is in the same terms that he is used to, that's why originally I asked for watts(P) not VA.

You can't really give him what he is asking for.
The problem is that they are measures of different things. Related - but different.
And different for different pieces of plant.
Difficult to know how to explain that without getting a bit technical and that will incur the wrath of the mods...............

The input to any piece of equipment can be expressed in kW or kVA. The kW input is, except in special cases, normally lower than its kVA and never higher. The ratio of total load kW/kVA is called power factor. If you don't know the power factor of the load supplied by the 500kVA transformer, and you likely don't in most cases, you can't calculate total power.

I think your only choice at this stage is to explain to you manager that it can't be done.
If he has an apoplexy, come back and we might be able to provide better wording than "can't".

 

[jumper]

I shoulda known that using "amps per phase" was gonna throw the OP off and he would try and add them.:slaphead: