Blar i SINTEF på forfatter "Aakre, Torstein Grav"

Viser treff 1-10 av 10

    • AC Breakdown Voltage of 50-Year-Old Service Aged Hydro Power Generator Stator Bars 

      Aakre, Torstein Grav; Ildstad, Erling (Peer reviewed; Journal article, 2022)
      Randomly selected generator bars from a 50-year-old Norwegian hydro power generator were examined in this work. Typical non-destructive tests, as partial discharge and dissipation factor measurements were initially performed ...

    • Comparison of Offline VLF PD Measurements and Online PD Measurements on a 50-Year-Old Hydrogenerator Stator in Norway 

      Eberg, Espen; Aakre, Torstein Grav; Berg, Gunnar; Hvidsten, Sverre (Chapter; Peer reviewed, 2018)
      Stator winding insulation is the part of the hydrogenerator experiencing the highest number and the most damaging failures. Partial discharge (PD) measurement, both offline and online, are commonly used for condition ...

    • Condition Assessment of Hydrogenerator Stator Bar Insulation Using Partial Discharge Measurements 

      Aakre, Torstein Grav; Ildstad, Erling; Hvidsten, Sverre (Chapter; Peer reviewed, 2018)
      This paper presents results from laboratory measurements of partial discharge (PD) activity in 50 cm long samples cut from the mainwall section of old hydrogenerator stator bars. All stator bars were manufactured in 1976 ...

    • Conduction and Electric Fields in Dielectric Liquids in Needle-to-Plane Gaps 

      Hestad, Øystein Leif Gurandsrud; Aakre, Torstein Grav; Lundgaard, Lars Esben (Peer reviewed; Journal article, 2024)
      This paper describes measurements of conduction currents in both neat and commercial insulating liquids. Conduction in thermodynamic equilibrium has been measured by applying a low ac voltage in a uniform field. High-field ...

    • Frequency Dependence of the Electric Field Grading of End-Winding of Generator Bars 

      Aakre, Torstein Grav; Enoksen, Henrik; Eberg, Espen; Mermigkas, Athanasios; Hølto, Jorunn (Peer reviewed; Journal article, 2022)
      To reduce the electric field stresses in the end-winding in hydropower generator bars, a field dependent grading tape is applied in the transition zone from outer corona protection to bare insulation. The design is typically ...

    • HydroStator : hovedfunn og resultater i KPN-prosjektet HydroStator 

      Berg, Gunnar; Eberg, Espen; Aakre, Torstein Grav; Ildstad, Erling; Kantar, Emre; Nysveen, Arne (SINTEF Rapport;, Research report, 2022)
      Modeller som beskriver temperatur- og frekvensavhengighet til elektriske delutladninger er utviklet og viser at tilstandskontroll med den mer praktiske VLF-metoden som benytter 0,1 Hz høyspenning er representativ for 50 ...

    • Modelling and Characterization of Partial Discharge Activity versus Applied Voltage, Test Frequency and Temperature 

      Ildstad, Erling; Aakre, Torstein Grav (Chapter; Peer reviewed, 2022)
      Measurements of partial discharges (PDs) are commonly used as diagnostic indicators for assessing the quality of high voltage equipment. In many cases, such PD measurements are of practical reasons either performed at ...

    • Multi-stress Cyclic Testing of Roebel Stator Bars for Hydropower 

      Eberg, Espen; Kantar, Emre; Aakre, Torstein Grav (Peer reviewed; Journal article, 2022)
      A multi-stress test rig was built to investigate the effect of many start-stops (load cycling) on hydropower generator insulation. To emulate real-life start-stops, stator bars were subjected to accelerated temperature ...

    • Transformatorgjennomføringer - Tilstandskontroll og anbefalinger 

      Eberg, Espen; Meyer, Hans Kristian Hygen; Foros, Jørn; Berg-Karlsen, Gunnar; Tveten, Erlend Grytli; Aakre, Torstein Grav (SINTEF Rapport;, Research report, 2022)
      Prosjektet "Tilstandskontroll av transformatorgjennomføringer" har hatt som mål å fremskaffe nødvendige metoder samt kunnskap for å kunne foreta en tilstandsevaluering av transformatorgjennomføringer. Hovedvekten av ...

    • Use of Data-Driven Approaches for Defect Classification in Stator Winding Insulation 

      Kantar, Emre; Cascallo, Jaume M.; Aakre, Torstein Grav; Thomsen, Nina Marie; Eberg, Espen (Peer reviewed; Journal article, 2022)
      Partial discharges (PD) in the high voltage insulation systems are both a symptom and cause of terminal and impending failures. The use of data-driven methods based on PD measurements will enable predictive strategies to ...