Energy loss in transformers

[electrofelon]

Anyone want to throw out a guess of what a typical dry type single phase 15 kva transformer would draw just sitting there with no load? Is there a rule of thumb for this? Anyone ever measured this (not necessarily with that specific KVA)?

 

[victor.cherkashi]

I guess 0.5% with no load

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[Jraef]

I guess 0.5% with no load

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Agreed. No-load losses are just from energizing the core and remain constant regardless of load. So the de-facto standard for determining those when calculating transformer efficiency is to always use 0.5%

The tricky part is, what does "no load" really mean any more? If you are powering up anything electronic, even if it's not being used, the power supply for it is probably consuming energy and creating harmonics, which are heating up the transformer, yet doing no useful work. A lot of electronic devices now are technically still powered up even if not "on". So I always tell people that unless you open a switch on the secondary side that totally disconnects it from everything, the transformer will likely have a load now. If you were going to do that, open it on the primary side if you can (obviously would not apply to a service transformer).

 

[Besoeker]

Agreed. No-load losses are just from energizing the core and remain constant regardless of load.

More or less so.

This is the Steinmetz equivalent circuit.

As the load increases, the current through X1 and R1 increases so the voltage applied to the Xm and Rm branch decreases.
For the great majority transformers (but not all) that can be ignored. But I'm a pedant.

 

[templdl]

Anyone want to throw out a guess of what a typical dry type single phase 15 kva transformer would draw just sitting there with no load? Is there a rule of thumb for this? Anyone ever measured this (not necessarily with that specific KVA)?

Being that you weren't very specific, I.E. 1ph, 3ph, ventilated or encapsulated, 80, 115 or 150 deg C rise, etc.
Losses can be as low as a bit over 155watts to as high as about 260watts.
Ask a ballpark we question and get a ball park answer.
Remember that the lower the temperature rise the higher the NL losses.

 

[electrofelon]

Thanks for the replies guys. Sorry, spaced on this thread for a few days.....

Being that you weren't very specific, I.E. 1ph, 3ph, ventilated or encapsulated, 80, 115 or 150 deg C rise, etc.
Losses can be as low as a bit over 155watts to as high as about 260watts.
Ask a ballpark we question and get a ball park answer.
Remember that the lower the temperature rise the higher the NL losses.

I am currently off-grid, but debating going on grid. If I did a 240->600 step up then back down, just wondering what I would be paying just for the transformer losses. I dont really have specifics on a transformer, just throwing it around. It would be single phase.

 

[templdl]

Thanks for the replies guys. Sorry, spaced on this thread for a few days.....




I am currently off-grid, but debating going on grid. If I did a 240->600 step up then back down, just wondering what I would be paying just for the transformer losses. I dont really have specifics on a transformer, just throwing it around. It would be single phase.

Have you identified the transformer you would like to apply? Have you thern contacted a transformer manufacturer providing therm with the transformer specification and simply AS THEM for the transformers losses. Simple. In my previous post I did provide to u with a some ball park figures basd upon the limited information as you provided. Anything more specific would have to be sourced from a manufacturer.

 

[Haji]

If I did a 240->600 step up then back down, just wondering what I would be paying just for the transformer losses. I dont really have specifics on a transformer, just throwing it around. It would be single phase.

Transformer losses depend on the size of the transformer also.

 

[mivey]

As the load increases, the current through X1 and R1 increases so the voltage applied to the Xm and Rm branch decreases.
For the great majority transformers (but not all) that can be ignored. But I'm a pedant.

Well pedant the big picture. Core flux inbreeding or what? I haven't really thought about it but you are correct that it is not constant.

 

[sparky7746]

If we know the transformer size and impedance can we calculate the the internal losses? I have a customer with two services and we are considering removing all the load from one service and putting it on the other so we can shut down a 2000 KVA transformer. I am trying to get an idea of the potential savings vs cost.

Thanks

 

[GoldDigger]

The size and the percent impedance will tell you what the resistive losses are at full load.
They will not tell you what the no load magnetizing current losses are though and that is something you need to know if the site will be at low power for two thirds of the day.

You can guesstimate the idling losses by measuring the idling current and assuming that the transformer was designed, as most are, so that the magnetic losses in the core and the I²R losses in the windings are approximately equal.

But for an accurate assessment you will need more information direct from the manufacturer.

 

[Jraef]

If you buy your transformer new, you can specify a TP-1 rated transformer, which is a new(ish) government minimum efficiency rating. That can make your decisions a little easier because it is more predictable.



Article:
http://www.csemag.com/single-articl...-losses/84a7466f05abe1341ddb4b5a402249e9.html

 

[Julius Right]

If we shall take 97.7% efficacy as per jraef article and 2.6% short-circuit impedance and 2.02/1.6 =X/R as per
General Electric Application Information Short-circuit Current Calculations Table 14 for 15 kVA
See:
http://apps.geindustrial.com/publibrary/checkout/GET-3550F?TNR=White Papers|GET-3550F|generic
we shall get 345 W total losses and 242 W copper losses[full load].Then no-load losses will be 103 W [in the range of 1/3 to 1/4 of the total losses as per above jraef article]