The Importance of Thermal Classification in an Ever-Changing World

Thermal classification of insulating materials used in large rotating machines is crucial because the service life of such machines is dependent on the performance of their insulation materials at the operating temperature. There has been a need to increase the required thermal performance of organic-based insulation binders to meet growing performance demands. These binders have evolved from NEMA Class B with a 130°C service temperature to NEMA Class F with a 155°C service temperature. Now there is a trend towards using NEMA Class H, with a service temperature of 180°C, in large rotating machines as manufacturers seek to boost output without significantly increasing the machine’s size. Class H organic insulation binders have been used in small-to-medium rotating machines for some time, but there are challenges when it comes to using them on a larger scale, especially with processes like vacuum pressure impregnation (VPI). One of the main complexities discussed is the dependence of the thermal classification of an insulating material on the method used to determine it. Different manufacturers, both suppliers and original equipment manufacturers (OEMs), may have their own methods and use different standards for classifying insulation materials, which can lead to different classifications of the same material.Additionally, the increasing demand for environmentally friendly or ’greener’ insulation binders, particularly bio-based options, poses a challenge. These newer materials may not have the same proven service life as traditional insulation binders, which can raise concerns about the affect the long-term reliability of large rotating machines.The paper aims to present cases of thermal classification based on different test methodologies and discuss the complexities facing the organic insulation binder industry as it adapts to newer, more environmentally friendly resin systems and the growing demand for their use.