Hi there all,
I was wondering... I have a 3 phase transformer and I'm trying to find
the current on the secondary winding.
My transformer is 415 primary 50Hz - 208 Secondary 50Hz
I have the current/power values for my primary winding.
Is there any way that I can find the current/power in my secondary
Is it: Is=Ep*Ip/Es ???
Thanks for your help... PS: If you need any more info, give me a shout.
On 7/13/06 8:18 AM, in article
I think you have it right IF your are talking the same winding configuration
on primary and secondary. That is Y-Y or delta-delta. Remember that the
power going into a leg of the transformer is the same as that going out.
-- Ferme le Bush
Salmon egg has it right but it would be easier if you gave all the data at
it appears that the transformer may be 415/208 line to line and 240/120 line
to neutral Y-Y possibly an autotransformer.
Don Kelly firstname.lastname@example.org
remove the X to answer
Hi there Guys,
I'll give you a bit more info.
I have recently started a job in a large manufacturing plant in the UK.
This plant has alot of American equipment/machines so voltages are
converted to 110 and 208v.
The plant has been having problems as previously there was no standards
or conditions for electrical loading on Distribution boards, eg. many
board were overloaded and many had very little loading... Therefore
leading to some transformers being close to their load limit.
I have recently carried out a survey on the distribution system and
have recomended changes, eg cables moved from heavey loaded DB's to
light loaded DB's.. this has been actioned and all seems ok... the
loads are now shared.
Within the plant there is a computer system monitioring the kW in
various boards, these are fed to a PC where loading can be checked etc.
5 of these readings come from 208v circuits.. eg to find the loading on
the transformers on the 208 circuits.
The problem I have is that when being installed in 1993 the contractor
then installed the CT's on the primary side of the transformer, eg 415v
rater than the secondary (i think they were cutting corners).
So now... when I get the reading I am getting the reading (kW) from the
primary side 415v and not the secondary 208v. This is not giving me the
correct reading as this is taking into consideration the transformer
power... I just want to see the power/current in my 208 side.
Here's the data I have from the plate on the transformer:
The transformer is: ABB Trafo-BB, Type DZV
Here's the reading i've takin for one of the transformers:
The line current is: 762A
The voltage is: 208v
so therfore the kW is: 247kW
These are manual readings... but the reading on the PC which is coming
from the Primary 415v side is 324kW.
*Note... these are approx values since its such a big num and from
different sources so any calculations will not be exact*
Its nearly impossible for me to install 110v or 208v CT's as the
equipment must be shut down.
Does anyone have any ideas how
Is there any way I can get around this... all I'm looking for is the
current or power on the secondary side.
I guess the decimal points are not at correct places - should be
The difference between 324 and 274 is 15%
The current at low voltage side in your case should be 2 times less
than on primary:
P(high voltage)C3V*sqrt(3)*Current(high voltage)*(power factor)
P(low voltage)!6V*sqrt(3)*Current(low voltage)*(power factor)
If we neglect the losses in the transformer - then P(hv)=P(lv), so
Current(lv)/Current(hv)C3/216=2 => Current(lv)=2*current(hv)
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