Transformer Insulation - A necessary component
Since the earliest attempts at utilizing the technology of a c (as opposed to d c), the transforming of voltage from one level to another has been in use.
The economics of moving power from one point (say generation) to another (usage) at higher voltage and lower current have been well understood – smaller x section of conductor etc. So having moved your power to the point of usage it is usually necessary to ensure it is available at the required or a convenient voltage. So devices to transform voltage were required at either end and a manufacturing technology was brought into being.
With production of transformers came the requirement for some insulating medium, not least between turns and particularly to earth, to ensure NO breakdown caused by voltage with consequent equipment failure occurring The original transformers were small, low kva, air cooled insulated with a variety of tapes and shellac or varnish to bind together. Demand for larger thro’put kva soon led to other thoughts and a system using forms of paper and refined oil came into being which in developed, modified form still exists today.
The perceived advantages were
- Various grades of paper were available. Paper can be an absorbent medium and by asorbing, say oil, can assume a di electric factor not unlike oil itself.
- Various fluids were available, crude oil being one such and even then being fractionally distilled to produce a variety of by products.
Specific disadvantages
- Water absorbent, reducing or eliminating insulant properties.
- General deterioration in properties of cellulose (irreversible) and oil (partly treatable).
The establishment of paper and oil as a suitable system of insulation came about by experiment (pure water might have been used, but its properties as an insulating medium are quickly compromised by a low degree of contamination). The other useful property provided by oil is as a cooling medium – oil possessing a reasonable thermal capacity and so usable to assist the cooling of any working transformer by acting as a heat transfer vehicle between the coils of the transformer and the means of dissipating such waste heat from the transformer.
So the paper/oil system came into being as the major technology supporting the manufacture of transformers of most voltages (except the very lowest) and power thro’put (again except the lowest) in use world wide. Since the early days much research has been conducted to improve the long term performance of materials used but the basic concept remains the same even in the 21st Century.
Bob Bennett