Electrical Degradation and Breakdown in ... - IET Digital Library

PART 5ENGINEERING CONSIDERATIONSFOR BREAKDOWN TESTING ANDDEGRADATION ASSESSMENTIntroductionIn earlier parts of this book we have reviewed the scientific understandingof electrical degradation and breakdown in polymers. In this part we wishto review and suggest techniques for assessing polymeric insulation systems.The first chapter in this section reviews current breakdown testing techniquesand the procedures which are used for analysing the data. The basisof these tests and procedures are examined and complementary techniquesare also suggested. We have noticed in the course of our experience withtesting cables under AC and DC conditions that there are significantdifferences in the statistics describing the results. Chapter 17 analyses thesetwo cases and indicates the differences in the techniques necessary forunderstanding the data. It also explains commonly observed, empiricalrelationships between AC and DC breakdown strengths and suggests thatthe build up of space charge may be the critical factor linking AC and DCbreakdown. Since extruded cables are a major user of polymers for insulationpurposes, Chapter 18 is devoted specifically to cable assessment procedures.Since these tests are currently being reviewed by many bodies we have notattempted to specify tests in any detail in this chapter but, rather, weattempted to identify the major considerations in carrying out such tests.Finally we have outlined some techniques for the non-destructive diagnosisof electrical polymeric degradation.