Answer / jc millar

When does the other KVA ratings come into play. For example consider
OA 55 C / OA 65C / FA 55 / FA 65 C.
Assuming the maximum demand process load is used to select the base rated KVA
i.e. OA 55C.
When do the other KVA ratings come into the load study ?
We understand the max. group motor load starting being = < 65 % Base KVA.
Can someone please explain.

Answer / nivin

1500kVA or 1500000VA
Roughly when the power factor is 0.8, it has an efficiency of 80%.
1500kVA x 0.8 = 1200kW or 1200000 Watts
Also considering other heat losses, another 10% more will be reduced.
So the practical possible load will be 1080kW or 1080000 Watts

Answer / arvi

It is interesting how much wrong answers can be gained with
one simple question. I assume that all people answered are
somehow involved with above mentioned theme. To avoid
problems and cost for you in future I´ll give you few hints.
First of all I want to remaind to everybody that
transformers are normally custom made equipment and to
answer this all transformer data has to be presented. Same
well you can ask how far can you drive with the car having
150kW engine!!!
1. I presume that such big transformer feeding not much
equipmnt stating its elektrical KW. On your engine
nameplate you find mechanical kW on engine axe. It has
nothing to do with engine electrical kW.
2. Transformer load is always calculated in Amps. And that
is information what you can always find on all and every
el.equipment as well as on the nameplate of your
transformer. Simple as that.
3. In normal cases you can not presume how many Amps you
will use as it is depending on the load on your equipment
what is varying in real life quite much. So you or use max
Amps stated on nameplates or expected Amps by your
specialists or you set up the Ampmeter and measure it.
4. Normally you dont want to load your transformer
permanently more than 75% as there are always swiching
processes giving load jumps upto few times more than the
full load of your transformer
5. It is very important to consider permanen distortion
level what your equipment emissing back to transformer and
the distortion level coming from higher voltage side. This
is complicated issue what is quite simple to measure, but
for that you really need specialist.
6. Distortion creators in your network are lighting,
smartequipment, variable speed drives, office technology,
UPS systems etc. If you dont have special converter type
transformer then you have to degrade the allowable load as
much you have the distorting equipment. If you have all the
load distorting for example then you dont want to load your
transformer more than half power only. To be honest then
even less, but its again depending on the type of
distortion.
7. Easiest and cheapest is always to ask specialist giving
you stright and exact answers. Trust me - it always pays
back. In this forum you have had answers from the level of
housewife to secondary school students. They are partly
right but non of them giving you really full answer.

Answer / plemieux m. el.

To calculate full load current, use this formula:

Amps = KVA÷Volts÷1.732x1000

Answer / amit sonmale

A=KVA/P.F
=1500/0.8
=1875Amp.
A= w/1.732*V*0.8
1875=W/1.732*415*0.8
1875=w/557.024
1875*557.024=w
W=1044420
Then KW=1044420/1000
=1044.42

why is efficiency of transformer more than that of other rotating machines?

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