transformers
transformers
(OP)
can someone plese check my calculation:
given: (3) 100 kva transformers.
question: what is the amperage output per transformer?
[(100 kva) * (.85 power factor)]/[(230 volts) * (sqrt(3)]=213 amps
if this is correct, does this mean i have 213 amps capacity
per each line?
given: (3) 100 kva transformers.
question: what is the amperage output per transformer?
[(100 kva) * (.85 power factor)]/[(230 volts) * (sqrt(3)]=213 amps
if this is correct, does this mean i have 213 amps capacity
per each line?






RE: transformers
RE: transformers
RE: transformers
If you are designing a new service and are looking at sizing an appropriate transformer you would typically start with adding up your components loading then pick the right transformer size.
for a 3 phase trasformer setup with a 230 V secondary and a 220 A full load current an 88Kva transformer would be the size. Some might oversize the transformer for future loads
For 230V secondary and 250 amps full load current a 100KVA rated transformer appears to be appropriate
go to http://www.elec-saver.com/freetool.htm
disclaimer: dont take my word for it though.
RE: transformers
RE: transformers
RE: transformers
I=kVA/(sqr3 x kV)=100kVA/(sqrt3 x .230kV)=251Amps
RE: transformers
If so,
100kVA / 230V = 435 amps
If (3) 100kVA 1-phase transformers are connected in a 3-phase bank, you effectively have one 300kVA 3-phase transformer.
300kVA / 230V / sqrt(3) = 753 amps
RE: transformers
100kVA/0.230kV=435Amps
300kVA/(0.230kV x sqrt3)=753Amps
i.e. the plain crunching numbers would not do.
RE: transformers
(3)100kVA single phase transformers will constitue a 300kVA 3 phase bank.
Stevedantonio should clarify.
RE: transformers
the set up is 3 separate high voltage lines coming into a transformer vault, therefore each transformer is connected to a single phase.
From the transformers, 4 sets of (4) 500mcm feeders go to a 1600 amp disconnect and ct cabinet.
RE: transformers
The 1600A Disconnect appears to be too high. Which size of fuses is inside?
kVAsec=sqrt3 x .230 x 1600=637kVA
for three single transformers connected in 230V delta on the secondary
kVAsec=sqrt3 x sqrt3 x .230 x 1600=1104kVA
for three single transformers connected in sqrt3 x 230V = 398V wye on the secondary
It looks like the single transformer may have the 120V secondary.
kVAsec=sqrt3 x .120 x 1600=332kVA
for three single transformers connected in 120V delta on the secondary
kVAsec=sqrt3 x sqrt3 x .120 x 1600=576kVA
This result would not be correct since the transformer could be overloaded.
for three single transformers connected in sqrt3 x 120V = 208V wye on the secondary
RE: transformers
If the secondaries are connected in a wye configuration then the rated output current of the 3-phase bank would be the same as for one of the three transformers.
300kVA / 0.230kV / 3 = 435 amps
As noted in the previous post, if the secondary overcurrent protection (OCP) is 1600 amps that may be too high. According the U.S. National Electrical Code, in unsupervised locations you are required to have secondary OCP set at not more than 125% of the rated secondary current of the 3-phase bank.
Are these transformers owned by a utility company? Is so, it may not be subject to code requirements. In the U.S., utilities commonly undersize transformers compared to the secondary disconnect size.
RE: transformers