Quality assurance testing for large air-cooled generator stator winding insulation

There is a growing trend to specify and use smaller generating unit sizes than was prevalent before. Furthermore, this new equipment is often operated at the limits of the design in order to maximize performance. In response to these pressures, electric utilities and independent power producers, are specifying large air-cooled generators with capacities of up to 300 MVA. Due to advances in materials and design, and consequently lower costs, these units compete effectively with hydrogen-cooled machines at these ratings. From a user perspective, there remain concerns which need to be addressed. Within this contribution, attention is focused on outstanding issues related to the problem of testing the stator windings of such machines. The paper discusses those areas of concern which are considered critical to the long term reliability of the stator windings of large air-cooled machines. In addition, efforts currently underway to address some of the issues thus identified are described.