The mechanical tests proved that the GP is the test that more effectively informs about the actual aging conditions of the insulating kraft paper, helping with the results.
The condition of the insulation paper in the transformers is the determining factor of the life of these equipments and that 50% of the mechanical loss of this polymer is generally accepted as limiting condition for use.
In the classes used, the 50% decrease in paper strength at breakage was reached after 33 days of aging, and equates to an approximate GP value of 475. However, in the field, as paper sampling is done in some parts of the transformer, there is a risk of sampling the part of the paper that has not been punctured. An indirect methodology, such as the measurement of furanic compounds in the IMO, is applied for efficient evaluation of the state of the solid insulation. HOR06FBYP34
Thermogravimetric assays (TGA) were also carried out on a new and aged Kraft paper sample for 35 days and the GPs for these samples were quite different, 1050 and 367 respectively, indicating the cleavage of the glucoside bonds of the biopolymer after aging. However, the results for thermogravimetric tests indicated only a small difference in temperatures where the degradation rate is maximal.