Establishing Stator Winding Insulation Systems Life Following Industry Standards for Thermal Classification

Current VPI and resin rich stator winding insulation systems are widely classified for thermal Class F. To achieve a successful service life, it is expected that a machine should last reliably when operating within specified temperature limits. To achieve a reliable life, it is assumed that maintenance protocols are followed, as per the OEMs instruction manual. The recommended standards to qualify or evaluate insulation systems for a thermal class are IEEE Std. 1776 or IEC Std. 60034-18-31. Typically insulating materials operating at their thermal class limit or temperature will degrade faster. To achieve a significantly longer operational insulation life it is common to maintain margin between the winding temperature rise above ambient and the winding insulation thermal class as specified by NEMA MG-1. In this paper, a comparative study of different industry standards is presented, explaining their differences for establishing a thermal class. In addition, experimental work is presented to show, how thermal classification for a 13.8 kV system is established along with the use of statistical tools.