Esters for use in distribution transformers
“The dielectric material most widely used in transformers is the conventional mineral oil. This technology has experienced very few variations throughout the years, except for the appearance of PCBs in the 1950’s, that were subsequently banned due to their toxicity.
Today, one of the new challenges we are facing is the promotion of a good environmental management and, therefore, the adaptation of dielectric materials to these new needs. Both natural and synthetic esters were conceived to this end.
The main advantages of esters as dielectric materials are the following:
- High compatibility with mineral oil and cellulose.
- Dielectric properties superior to mineral oils.
- The water saturation point is high, thus maintaining high dielectric rigidity values in the presence of water.
- They slow down the degradation of cellulose when oil is displaced by water.
- High fire resistance: They have a high combustion point, reaching that of silicone.
The negative aspects of esters, if compared with mineral oils, are:
- Higher oxidation mechanisms in the presence of oxygen.
- Higher viscosity levels.
- Decrease of properties at low temperatures.
Since it is a relatively new product, there is little experience of use. Regulations concerning synthetic esters are reflected upon IEC 61099:2010, and currently an IEC standard is under development to include natural esters.
The use of esters as dielectric material in transformers has increased in recent years. Thus, in order to respond to this new need, ceis has included this product within its laboratory tests.