Degradation of Epoxy in Stator Insulation in Service 23 Years for A Large Generator

The degradation behavior of epoxy in stator insulation under operating stresses was invested by thermogravimetry and infrared spectrometry. The insulation specimens were cut from a standby and an aged stator bar in operation for 23 years in a 300MW/18kV generator. It is found there are two aging processes of epoxy in the aged insulation. One is weight loss measured by thermogravimetry increases, while the absorption intensities due to ¿OH, C=O groups increase, and those due to ¿CH3, ¿CH2 groups obtained by infrared spectrometry decrease, demonstrating the oxidation occurred on branched chains of epoxy. The other is more two decompose processes appear in the TG curves, in addition to decompose of epoxy, while the absorption intensity due to C-C group decrease, revealing the rupture of fundamental chains of epoxy.