Dielectric Dissipation factor measurements on stator insulation - results from a global survey

Dielectric Dissipation Factor (DDF) measurements are used to assess the manufacturing quality of individual stator bars/coils and the dielectric behavior of the electrical insulation system of stator windings. The use of this diagnostic test method is widespread and standardized in IEEE and IEC documents. The new IEC 60034-27-3 document sets acceptance limits for individual stator bars and coils based on parameters such as the absolute value of DDF and DDF tip-up at specified voltages. These requirements are viewed by some as too restrictive and by others as overly lenient. Therefore, in 2012, CIGRE established a working group to survey experience with and collect data on DDF testing of newly manufactured stator bars and coils on a worldwide basis. The collected DDF measurement results were analyzed in relation to various influence factors and the results were incorporated in a technical brochure. This contribution will discuss some of the key findings of this work of great significance that was published by CIGRE in 2019.