B. Absorption in thick cellulose materials
An important parameter for the construction of transformers
is the impregnation of the cellulose insulation. As the viscosity
of the ester composition differs from these of standard mineral
oil, investigation of its impregnation behavior was necessary.
Three different insulating materials have been tested:
pressboard, laminated board and laminated wood. And the test
results show that behavior of the low-viscosity ester
composition concerning the oil absorption in the tested solid
insulating materials is slightly better than that of a synthetic
ester which is already used in transformers. [2]
C. Ester and paper ageing
The oxidation stability assessment of insulating liquids is
an important issue, especially in the case of natural esters
which are intrinsically less stable than petroleum products. One
way to address this matter is to compare the performances of
esters and mineral oil submitted to the same ageing test. So
investigations have been performed in parallel with both a
standard insulating mineral oil (paraffinic, uninhibited) and the
ester composition. As there is not yet a standard applicable to