BS PD IEC/TR 62874:2015, which is a Technical Report provides guidance for the estimation of consumedthermal life of transformers' cellulosic insulators, through the analysis of some compounddissolved in the insulating mineral oil. A comparison between analytical results of 2-furfural(2-FAL) and carbon oxides and their correspondent typical values estimated for differentfamilies of equipment gives information on the estimated thermal degradation of papers.The ageing rate of insulating papers can be evaluated, in short time ranges (e.g. 1 year), byregularly monitoring 2-FAL and carbon oxides content in the oil and by comparing them totypical rates of increase.A statistical approach for the estimation of paper thermal degradation, and the evaluation ofageing rate is given.Typical values for concentrations and rates of increase of the parameters related to paperageing were extrapolated from a statistical database collected, and are reported in Annex A.They may be used as a rough guide, but they should not be considered as threshold values.This Technical Report is only applicable to transformers and reactors filled with insulatingmineral oils and insulated with Kraft paper. The approaches and procedures specified shouldbe taken as a practical guidance to investigate the thermal degradation of cellulosicinsulation, and not as an algorithm to calculate the actual degree of polymerization (DP) ofpapers.The paper thermal life evaluation protocol described in this Technical Report applies tomineral oil impregnated transformers and reactors, insulated with Kraft paper. Any equipmentfilled with insulating liquids other than mineral oil (i.e. esters, silicones) or insulated with solidmaterials other than Kraft paper (i.e. TUP - thermally upgraded Kraft paper, syntheticpolymers) is outside of the scope of this Technical Report.This Technical Report is applicable to equipment that has been submitted to a regularmonitoring practice during the service, and for which maintenance and fault history is known.Cross References:CIGRE WG D1.01.10IEC 60076-7IEEE Std C57.91-1995CIGRE WG D1.01.TF13IEC 60450IEC 60567IEC 60814IEC 60970IEC 61198IEC 60666IEC 60599