Transformer Calculations

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Gmk

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I am looking for the best fomula to convert Megawatts into Kva. I am looking at a 7.5MW Transformer,12.4KV Primary, and 4160 secondary, and have been asked to convert to Kva.
Thanks,
GMK
 
You convert ?mega? to ?kilo? by multiplying by 1000. So a ?7.5MW? transformer is the same as a ?7,500 KW? transformer.

But transformers are not normally described in terms of watts. Their ratings are generally given in terms of VA. Are you certain that you did not start with a ?7.5MVA? transformer?

If this is just an academic question, then the rest of the answer to your question is that you convert ?Watts? to ?VA? by dividing by the ?power factor.? Since you did not give us a value for power factor, I can only say that we don?t have enough information to solve the problem. You can assume a value if you like, perhaps 0.8 or 0.85 might do. But the person who posed this question to you will have to provide a value for power factor, or will have to allow you to assume a value, or else the problem cannot be solved.
 
Gmk said:
I am looking for the best fomula to convert Megawatts into Kva. I am looking at a 7.5MW Transformer,12.4KV Primary, and 4160 secondary, and have been asked to convert to Kva.
Thanks,
GMK
Click to expand...

You need to multiply your MW value by 1000 to get a KW value. This will also be your KVA value at a power factor of 1. If there is a power factor involved, most generators and transformers I have seen are rated at a .8 power factor, this value will have to be used in your calculation also. A simple relationship between KW and KVA is as follows:

KW/KVA = PF

Just a note. Although most transformers and generators are rated at a .8 power factor your actual power factor is determined by the load.
 
If I understand this corectly, now that I have my Kilowatts, and figure he power factor is .8, I can nw calculate my amperage. KWx1000/Ex1.73x.8
then I can calculate my KVA by the calculation IxEx1.73/1000, is this correct am I on the right track, or is there a better way?

Thanks for the help.
GMK
 
Gmk said:
I can nw calculate my amperage. KWx1000/Ex1.73x.8
then I can calculate my KVA by the calculation IxEx1.73/1000, is this correct am I on the right track, or is there a better way?

Thanks for the help.
GMK
Click to expand...

Those formulas are correct
 
The only way to correctly size a transformer is via the kVA values of the devices, not guessing at a PF value. And, you must also take into accout any motors that start more than twice an hour, the ambient temperature and altitude. This is assuming that your circuit harmonics are fairly normal and a K factor rated transformer is not required.
 
Snorks said:
The only way to correctly size a transformer is via the kVA values of the devices, not guessing at a PF value. And, you must also take into accout any motors that start more than twice an hour, the ambient temperature and altitude. This is assuming that your circuit harmonics are fairly normal and a K factor rated transformer is not required.
Click to expand...

Unfortunately, he did not ask how to size a transformer, only how to calculate the KVA from KW.
 
Without knowing the PF of the circuit, you can not accurately determine kVA from kW. The circuit PF can only be established from the kVA and kW values of the devices.
 
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