Ester oil - Foot print reduction in oil filled Transformers 1

[NickParker]

I read that usage of ester oils will reduce the size and weight of the transformer. I'm unable to understand how as the higher viscous nature of ester oil will increase the oil temperature rise, winding temperature rise, winding gradient and hot-spot temperature due to less convective heat transfer.

 

[Gr8blu]

Nick: You are correct - the ability of esters to effectively transfer heat is somewhat less than traditional mineral oils. (Mineral oil = 125.7, natural ester = 111.8, and synthetic ester 110.7 - all units are W/m2/K).

The net result is that for a given volume of liquid and a given thermal "starting point", the traditional mineral oil will keep the windings and their insulating materials about 1.1 to 1.2 degrees C cooler than either natural or synthetic esters. However, esters will, in general, withstand higher temperatures before their insulating properties are degraded.

On the ester "plus" side is improved biodegradability of the liquid, lower toxicity, high flash point, and low caloric value. On the mineral oil "plus" side is lower cost-per-unit-volume and higher regional availability.

It comes down to this - the transformer vendor is more interested in volume sales than in providing a durable product (planned obsolescence? limited life?). Since the ester coolant can be worked "harder" (e.g. it doesn't catch fire as easily and, due to biodegradation and reduced toxicity, is a favorite of "green" thinkers) and the train of thought that "a winding can always be replaced", transformer vendors - or at least their coolant suppliers - tend to argue for ester. Does it really reduce the transformer physical size? Sometimes - but then the question becomes whether it is truly the change to esters or a change in the transformer design (i.e. cooling circuit) that does the trick.

Converting energy to motion for more than half a century

 

[RRaghunath]

Whether traditional mineral oil or Ester, the winding insulation remains to be Paper that is rated to be Temperature Class-A.
It is this Class-A which limits the allowable winding temperature rise to 105 degC, isn't it!

R Raghunath

 

[prc]

The footprint of an ester-filled transformer will be the same or slightly more than the mineral oil-filled transformer with the same performance parameters

 

[NickParker]

Is it safe to say that, given the ability of Ester liquids to function at elevated maximum liquid temperatures, transformers can be engineered to operate at higher temperatures? This would potentially result in a decrease in the size and weight of transformers, without compromising the lifespan of the transformer.

 

[dik]

Does this mean that with ester 'oil' the transformers run at a hotter temperature? If so, does that have an impact on the winding or efficiency? Not a sparky...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[prc]

Even though esters are capable of higher temperature rise, there are limitations as long as the cellulose kraft paper is used for conductor covering. But ester will give a higher life for the same type of paper compared to mineral oil. Hence, for the same life expectancy, with esters, you can allow a 10C higher winding rise with ordinary kraft paper(thermal class 105) and a 20C higher temperature with thermally upgraded paper. Then copper losses will increase and suffer in efficiency (See appendix C of IEC 60076-14 on Power Transformers). If higher temperature rises are allowed, then the footprint may be the same as with mineral oil and without any reduction.