Increasing Transformer Capacity

Hi Sir

Thanks for your valuable information, Sir Transformers have protection against over temperature (winding temperature, oil temperature alarm and trip), I mentioned that now the cooling method is Oil Forced Water Cooling, Sir the absence of cooling increase the temperature rapidly on lighter loads too so the increase in cooling can add a little more load extra? It's just a doubt, Sir Can you please tell me some new methods of cooling for transformers

The foundamental thing you need to take in consideration Jay is the design of the transformer, if this transformer uses nomax insulation it can withstand excessive heat without breaking down, although I am not one that believed in overloading a transformer then depends on additional cooling methods to compensates. The next important thing to know, what type of oil this transformer is using, is the cooling process is a ONAN? If it is, depends on the size of the transformer other type of oil that manufactures use as a good insulation and cooling purpose is the R-Temp. You can increase the transformer's capacity by so much, then you will start to run into PF problem, voltage drop because the current increases etc. I just realize that you using oil force water cooling therefore it is not ONAN, therefore you cannot used the R-temp oil it is too thick for the pumps. My final recommendation is, if you need this extra capacity just decide to get a new transformer that can handle the load because if you even find a way to satisfy yourself to cool this transforemer it is going to fail not too long down the road anyway.

Regards

Granville

Thanks Mr. Granville, for introducing new transformer oil (R-Temp). Sir please tells me some of the new methods used today for transformer cooling and some more abut R-Temp oil.

Regards

JK

Hello jaykrish.

For the most part I agree with the original poster, not necessarily that it couldn't be done, but it probably shouldn't.

I have seen blower motors in air-conditioning units that were incorrectly set up pulling almost three times their rated load amps, the only reason these motors survive is that they were in the air stream basically the more air they pulled the more cooling of the motor.

In that situation (which I corrected) they even had a limited built-in safety factor, that is if a belt broke and they lost their additional cooling, the load also went away.

As a previous poster mentioned, if you cooling system fails, the load on the transformer doesn't go away, this could lead to an immediate failure, high current flow, the coils heating up, increased resistance, basically you have a cascade failure.

Transformers failing in this manner are not only expensive but dangerous, I think we've all heard one exploded some time in our life.

So while you're ideas correct, you are also bypassing the engineered safety factors, I'm sure when the unit was originally designed they took in the possibility of a cooling failure, and designed the transformer to at least operate for a limited period of time with reduced cooling.

Though the previous is somewhat speculative, it's good engineering practice to build in a safety factor, and significantly overloaded transformer experiencing a cooling failure would not only rapidly fail, but also could fail even if it was shut down at the point of cooling failure due to the residual heat not being dissipated.

So while I think you're ideas about increasing cooling capacity is a viable one, I do not believe it would be something that you would want to do for a long-term fix.

Hi Sir

Thanks for your valuable information, Sir Transformers have protection against over temperature (winding temperature, oil temperature alarm and trip), I mentioned that now the cooling method is Oil Forced Water Cooling, Sir the absence of cooling increase the temperature rapidly on lighter loads too so the increase in cooling can add a little more load extra? It's just a doubt, Sir Can you please tell me some new methods of cooling for transformers

The cooling (oi) in transformer takes away the heat from the surfaces available and dissipate it.

So while you can keep the iron cool, the windings can not be effectively cooled, due to the insulation over it. This insulation is electricall as well as thermal one. So while you cool the surface of it, the core, in coontact with copper remains relatively much hotter. And increasing the current will only make it more so and make it deterioate faster.

In large electrical machines (generators) due to this fact the copper are directly cooled by Hydrogen, water or any other cooling fluid.

All transformers are designed to take a bit of overload, but that can not be treated as capacity increase or for a long duration.

So the external cooling are unlikely to solve your problem. May be better option is to dispose it off and buy a larger capacity.

In large electrical machines (generators) due to this fact the copper

are directly cooled by Hydrogen, water or any other cooling fluid.

>>>>Don't forget the flashpoint of Hydrogen<<<

j.

In absence of Oxygen?

Large Generators are Hydrogen cooled (and are manufactured at our facility)

Hi Sir

Likes to tell me about this Hydrogen cooling method for large Generators.

Regards

JK

The coils made are hollow and are cooled by recirculation Hydrogen.

Due to large spacific heat capacity Hydrogen works verywell, only the leakage is fatal and has to be controlled.

Look at these links

http://www.gepower.com/prod_serv/products/generators/en/downloads/generators.pdf

http://pepei.pennnet.com/display_article/154893/6/ARTCL/none/none/1/Adequate-Cooling-of-Generators-is-Essential/

Sometimes adding cooling and increasing load works. If your transformer is custom made (less than 6 per year of that model) then you are on very thin ice if you try to increase its rating in this way. If yours is one of hundreds made per year, your odds of succeeding are not bad. I have done autopsies on too many multimillion dollar units that died after some extra cooling did not offset a bit of extra current, even though the oil temperatures looked promising.

The problem lies in the way these things are designed. There are likely to be design weaknesses with custom units. Uprating, with a coil cooling passage that is not big enough, will result in insulation failure due to excessive hotspot temperature.

After a zillion hours of design effort, Formula One cars still break. After 5 million copies are in service, a production car will not break in the same ways or at the same rate.

Earlier postings are generally correct. The option of changing the unit for a higher rated one is best, if you can find one.

David

You have not mentioned, what is the increase in capacity you are expecting. At best you can get a few percentage increase in capacity by improving upon cooling, e.g. keeping the water temp. to as low as possible which will tend to extract greater heat from the oil ( primary heat exchanger ). If you can add radiators to the existing tank then increase in capacity would be higher, but then that is a MAJOR CHANGE.

In the process you should also be prepared to accept higher impedance drop in transformer resulting in reduced terminal voltage, unless you have taps to compensate for same.

Last but not the least, is it worth doing all this exercise if it is going to marginally increase the capacity along with greater associated "risks", as I call it.

Thanks and regards

Ashok Toshniwal, Bangalore, India

Cooling is not the only problem. Transformers are designed for a given load. If you increase the load the flux in the core will also grow and after a value the core will be saturated, the flux will "leak" and the efficiency of the transformer will decrease. At the same time the secondary voltage will fall.

Hi jaykrish,

No one so far has seen fit to raise the subject of your power factor as this not only affects the carrying capacity (effective power) of your cables but also the transformer. If your heating load is purely resistive you are not going to gain much benefit on the load side but if the primary side pf is low then there is still scope for improved output capacity.

While I agree that power factor does affect the "effective power" being delivered to the load, but in this case, it does not matter because load is fixed and cannot be changed. Even if pf is improved by putting capacitors on the input side, then current DRAWN FROM FEEDER SUPPLY WILL REDUCE but CURRENT IN TRANSFORMER WINDING WILL NOT CHANGE. Hence transformer capacity will not improve. "Effective capacity" can improve if load pf improves, which is not possible in this case since application is fixed.

Thanks and regards

Ashok Toshniwal, Bangalore, India

Deep topics cannot be dealt with well in this way. Like trying to solve a nation's problems while you stand in line with strangers.

There are a lot of factors. If the transformer serves rectifiers, the harmonics will lead to far greater than expected heating. Any transformer engineer experienced in buying or manufacturing should be able to go through a long checklist and recommend a solution. Without such a checklist, we are all stabbing in the dark.

An appropriate and succinct reply if I may say so. Well done! It is only natural for respondants to try and be helpful(mostly) but I am concerned by a tendency to offer 'solutions' which cut corners and miss the bigger picture. Perhaps as responsible engineers we should be less willing to become involved in situations which could become risky through this process of abreviation.

Can the <...we...> get on the phone to the original equipment manufacturer and discuss it directly?