Determination of Transformer Rating

Contact the transformer manufacture.

Have you:

1. Assured that the transformer is real???

2. Contacted the manufacturer of the transformer?

2. Asked the person who gave you the assignment?

3. Nameplate?

4. Etc. Etc. Etc.

The transformer exists? And someone wants to add fans??? And wants to know what?? The "rating"?

This isn't homework is it?

Temperature Rise and Transformer Efficiency - Copper ...

Current transformer - Wikipedia, the free encyclopedia

K-Factor Defined

K Factor Chapter 3 - Federal Pacific

Where have you looked so far?

Yes I have assured all your questions. I have to gauge transformer capacity based On additional fans!he said the transformer rating might have increased to 13.33 mva from 11 mva but he is not sure about it and wants me to find out

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Well, on what design basis were the fans installed and on what basis was the necessary expenditure approved?

Is the wiring and are the circuit protective devices each side of the transformer suitable for the proposed increased duty?

Is there an Electrical Engineer on site that could answer the question?

The fans are already installed. The transformer is working at some higher rating and I have to determine that increased rating.

Measure its amperage.

PW: I will answer your questions, because telepathy tells me the answers!

1. The transformer ran out of capacity, so they want more and had to do something. Fans were cheaper than a whole new transformer.

2. Maybe not, but due to budget contraints the approach will be to run them until thermal failure.

3. No.

Good guesses.

I imagine you could gain only 5-10% above its existing rating. It will depend on the air flow arrangements more than on fan model and rating.

I think, your boss asked you to get the Transformer rating in AF condition. Look at the name plate . For eg;- AN/AF - 1000/1500KVA

I have come across transformers of French make rated 6MVA w/o fan & 9MVA when fans are switched on.

Simple. Load it up until smoke comes out, then reduce the load by 25%.

At least the new fans will blow the smoke away!

Seriously, on what basis was the expenditure on additional fans justified? For some reason, rather than replace the transformer with one of a different, known, rating, the project concept was based on adding fans to the existing. That calculation will exist in the scheme upon which the investment was authorised. It is rather surprising that at this late stage in the project, the basis for fans rather than replacement has been forgotten/put in a drawer/shelved/filed rather than being available for review.

So start digging through the project paperwork. It will be in there somewhere. Good luck with the search.

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It is class OA transformer, Type SL,2000 kva, hv is 69kv n lv is 7.2/14.4 kv Temp is 55 deg C Since it is class OA its not solid insulation will the problem of hotspots matter? I read smwhere that by adding single bank of fans( m nt sure what that means) there is a 33% capacity increase. Do u have any idea on this?

Hire a consultant. You are lost.

What does the controlling specification have to offer?????

You do have one, right?

Have you asked the supplier of the device, or, is that too easy.

None here. The transformer manufacturer might, though. How did the phone call go?

Surly you jest.

Additionally to what others have said, hire a consultant to perform the design calculations and take the risk.

A 2MVA transformer is not a toy, if you are not qualified to perform the calculations and something goes wrong or someone gets killed the transformer warranty is void (for a start) and you will field the blame and possible jail time, not the person who tasked you to perform the work.

This type of work should be done, or at the very least approved and signed off by professional consultants. That's their job.

Additionally consult the transformer manufacturer for advice as there is no single magic number you should use.

Variations in transformer design, fan type and implementation, air flow, hot spots, internal transformer tank construction, local environmental conditions effecting air flow and heat dissipation, transformer uprating reliability analysis, site location, etc mean that it is not as simple a task as you might think.

This is why transformers with fans can look quite different than transformers without fans from the same manufacturer, and why careful design analysis is necessary when making these type of changes to expensive distribution level transformers.

_{Jack - Actually working in the relevant industry.}

Huh? Just a while ago it was 11 MVA (or 13.3); now 2000 kVA (= 2 MVA)?

There are two transformers of different ratings

...and you wait until now to tell us? Sheeeesh.

A type OA transformer is oil (O) filled and air (A) cooled, and in both cases, no mechanical means are used to move either fluid (no pumps, no fans), instead relying natural cooling via convection, conduction and radiation.

The rated rise and hotspot temperatures are the most important operational numbers for you to follow once it is loaded to its nameplate MVA and temperature. Unless you read that 33% in the manufacturer's literature the best you can do is 15% (according to Westinghouse product sheets) and still be within the factory limits, after that you're on your own, taking years off of the expected life as you exceed the temperature/loading limits.

Sorry to say but when you said "...( m nt sure what that means)..." you indicated that this task is not for you to handle. Follow the advice of the other posters and ask your management for some professional help.

By saying ' m not sure what that means' I was talking about single bank of fans regarding their rating or air flow.can you tell me the site where u got the product sheets?

Sure, Google on your own words, "class OA transformer, Type SL,2000 kva", from your previous post.

In the UK there used to be a children's television program call Jackanory. Fanciful stories for children.

I think we've found out what happened to it.

Hi AKP

The tranformer rating is what is shown on the name plate. To determine the loading on the transformer after you added the fan, you measure the current or power using a power meter with clamp on leads, or a data logger to find out the maximum power drawn. Take the measurements at various times so you can see when the maximum and minimum loadings occur. Compare the maximum current or power reading with the rating of the transformer to determine if the transformer is overloaded or has space to cater for more increase in load.

Is the Transformer primarily limited by thermal factors (heating/copper losses)? or by saturation?

If it is thermally limited, cooling may give you some additional output capacity, but contact the manufacturer for details.

If it is limited by saturation, no amount of cooling will give you any output gains.....

Actually the parameter that governs saturation is flux level, and flux level is determined by the voltage and frequency across the winding, not by the load current. A transformer that is unloaded but subjected to voltages greater than 1.15 (+/-, depends on the properties of the core material, its construction, etc.) times its rated voltage will be at the edge of saturation.

The core losses are constant upon energization and do not depend upon the load current; I²R losses are the load variable (copper) losses that we are talking about here.

Is not the Flux 'Amp-turns'? - input current x primary turns.

Output voltage is input voltage x turns ratio - losses(copper, core)

Output current input current / turns ratio - losses

if the load increases, it means that the output current is increasing, therefore the input current is increasing, and yes the copper losses increase by the square of the current, but the flux also increases proportional to the current. which limit is reached first depends on the transformer design, and the margin built in.

Ampere turns (AT) is the MKS unit of MMF, but Flux is measured in Teslas, they're different but related. It's a common misconception that winding current causes saturation of the core, but that's not the case for ordinary power transformers.

From the IEEE Fundamentals of Power Electronics Chapter 12: Basic Magnetics Theory pg. 30

"...Transformer saturation

• Saturation occurs when core flux density B(t) exceeds saturation flux density Bsat.

• When core saturates, the magnetizing current becomes large, the impedance of the magnetizing inductance becomes small, and the windings are effectively shorted out.

• Large winding currents i1(t) and i2(t) do not necessarily lead to saturation. If 0=n1i1+n2i2 (the numbers are subscripts) then the magnetizing current is zero, and there is no net magnetization of the core.

• Saturation is caused by excessive applied volt-seconds

• Magnetizing current depends on the integral of the applied winding voltage

•Flux density is proportional to a constant times the integral of the applied voltage

•Flux density becomes large, and the core saturates, when the applied volt-seconds are too large..."

The condition "0=n1i1+n2i2" is typical for power transformers since whatever current flows into the transformer is the same (as modified by the turns ratio) as the current that flows out. Notice that except for this equation, winding current plays no role, it is the applied voltage and frequency that governs the saturation.

We also dont know how because we dont see any information infront of us...you say you have name plate info....we cant help if we dont see that info

A lot has been said which is relevant, but it really is this simple:

Transformers have a nameplate rating, which you indicated you have. The rating will read something like (fictional example) 2000/25000/3000. The ratings mean something like: air/forced air/circulating oil - depending on the transformer.

For a transfomer that's nampeplate just says one value, and did not come with fans, then it is rated for air, and unknown for other forms of cooling. Anything that we come up with here will be an educated estimate based on knowledge of the workings of things. Not a rating. Rated means the transformer was designed and intended to work within specifications for that application.

There are many things that you can do to get more capacity out of the tranformer - but that does not mean it was rated for it. You added fans. You could perhaps put an oil circulation system on. You could install cold water sprinklers that constantly cool the transformer. You could build a building around it and install air conditioning.

However -still not "rated".

Estimates? I would estimate that you can run a transformer to 125% of its rated value without burning it up. I would estimate that by adding fans that move some serious air, you could get between 10-33% more capacity.

These things would depend on the fans, the air flow, and the configuration of the heat sink fins/fan installation. Wouldn't they? (Yes they would!)

Do you have any litreature that explains this estimation?

No, I do not. That's why it is an estimate (maybe even a "guess") on my part. - Not something that should be done lightly. If the estimate of the capacity is wrong, depending on any of the multitude of factors, the transformer will be damaged and significant unhappiness will occur.

If there was a specific formula to be used, it wouldn't be guessing.

If the transformer is built to ANSI or NEMA standards then the 11MVA would be 13.75 MVA fan cooled. Those standards state that a self cooled OA or ON transformer of that size will have a 1.25 % increase due to the addition of fans. The clinker is that the only way you can find out what fans to add and the catalog number is to go back to the manufacture of the transformer. They will charge for the fan package which will include fans and a new nameplate. If you add different fans, and quantities you will get different answers. A guess could be made that as long as you keep the same top oil temperature after fan addition and load increase, you might be all right, but you could exceed hot spot rating which is where transformers fail, the hottest spot in the winding. Since you cannot measure that unless you have an AWR guage (hot spot) installed. If you have that, go by that and make sure you don't exceed standards. If your transformer is built to other specifications, you must look up those specs. Many use the same 1.25 for fans but not all do.

I am going to correct myself. I really don't remember the cutoff point for the different levels of fan control. 10 MVA gives a 125% increase (sorry about the errant decimal) and 12 MVA gives a 133% increase. I don't have the standards in front of me right now and can't remember the cutoff for sure but I think it was 10001 KVA where the 33% increase occurs. If that is the case, the value would be 14.63 MVA. Also many manufacturers also can provide a total OA/FA/FA ratings with more fans going for a 66% increase. The nameplate should list the standards the transformer was manufactured to and you can look up those standards on the internet. The 2000 KVA unit will have only a 15% or 25% increase depending on what standards it was manufactured to. If you do not have an AWR device, which I doubt you do on the 2000 you really need to go back to the manufacter. Different types of windings have different hotspots and this is difficult to guess at. I spent a lot of years in transformer design and it is a complicated process to calculate a hot sport even when the design and build is accurately known. The hot spot is what will catch you.

Well in nothing else when this transformer burns up you will have a nice set of brand new fasn to put on your next new and properly sized transformer.

Just out of curiosity why is the old transformer not being replaced by a larger one and then re purposed to another location elsewhere that has a smaller transformer that is running at its limit?

Rather than change the transformer, wouldn't it be easier to go for modern high-efficiency lighting instead?