Variability of Dielectric Measurements of Stator Bars Performed at Different Manufacturing Plants

It is a well-known experimental fact that tests performed on seemingly identical conditions on seemingly identical stator bars will produce different results [1] , [2] . That is due to a variety of factors and parameters whose influence on the measuring process, in spite of all care, cannot be fully controlled or reproduced. In addition to that, attaining the mentioned "seemingly identical conditions" is, by itself, a task of remarkable challenge and cannot be always achieved. In this context, the purpose of the present work is to describe the efforts and the findings involved in a 3- year test campaign designed to assess the variability of test methods among several different hydro- generator manufacture plants within the Andritz Group worldwide to (i) characterize the existing level of variability among the different manufacturing sites and (ii) identify eventual areas of improvement, whenever needed. The study was focused on some key dielectric measurements, such as Partial Discharges (PD), Dissipation Factor (DF) and Outer Corona Protection (OCP) Surface Resistance. These parameters are used worldwide for manufacture quality control and also for customer specifications of individual Roebel bars and multi-turn coils [3] , [4] . Therefore, the knowledge of their variability behavior has great practical relevance.