Browsing Institutt for elkraftteknikk by Author "Aakre, Torstein Grav"
Now showing items 1-17 of 17
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AC Breakdown Voltage of 50-Year-Old Service Aged Hydro Power Generator Stator Bars
Aakre, Torstein Grav; Ildstad, Erling (Journal article; Peer reviewed, 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, 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 Hydro Generator Stator Bar Insulation Examination of PD void activity versus AC voltage magnitude and frequency
Arctander, Stine (Master thesis, 2020)Innføringen av væravhengige fornybare energikilde i det eksisterende nettet vil påvirke det nåværende driftsmønsteret fra strømproduksjon vi kjenner i dag. Når man kombinerer energikilder som sol- og vindkraft med ... -
Condition Assessment of Hydrogenerator Stator Bar Insulation Using Partial Discharge Measurements
Aakre, Torstein Grav; Ildstad, Erling; Hvidsten, Sverre (Chapter, 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 ... -
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 ... -
Investigation of PD formation on AlN Ceramic Substrates: Impact of Square Voltage Pulses and Dielectric Liquids
Smisethjell, Ingrid (Master thesis, 2023)Det elektriske kraftsystemet gjennomgår en kompleks utvidelse og opplever raske spenningsendringer som skyldes endringer i driftsmønsteret. Disse forholdene har betydelig innvirkning på komponenter og utstyr i strømnettet, ... -
Limitations Regarding Use of the ABC-Model for Interpretation of Partial Discharge Measurements
Aakre, Torstein Grav; Skattenborg, Regina; Ildstad, Erling (Journal article; Peer reviewed, 2019)The main purpose of the work presented here is to facilitate use of partial discharge (PD) measurements as a diagnostic tool for condition assessment of hydropower generator bars. The main aim of the work is to clarify how ... -
Modelling and Characterization of Partial Discharge Activity versus Applied Voltage, Test Frequency and Temperature
Ildstad, Erling; Aakre, Torstein Grav (Chapter, 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 ... -
Partial Discharge Activity in Rotating Machine Type II Insulation Systems as a Function of Temperature and AC Supply Frequency
Aakre, Torstein Grav; Kantar, Emre; Eberg, Espen (Peer reviewed; Journal article, 2023)The main purpose of this study was to investigate if the application of very low frequencies for PD measurements in type II generator bar insulation is relevant when compared to applying power line frequency at different ... -
Partial Discharge Inception in Ceramic Substrates Embedded in Silicone Liquid, Silicone Gel, and Mineral Oil at Fast Voltage Rise and Sinusoidal Voltage
Semenov, Ivan; Aakre, Torstein Grav; Folkestad, Ingrid Gunheim; Smisethjell, Ingrid; Niayesh, Kaveh; Lundgaard, Lars Esben (Journal article; Peer reviewed, 2024)This paper summarizes experiments that were carried out on insulating ceramic substrates and a needle-plane arrangement with the purpose to characterize the inception of partial discharges (PD) in the insulation of ... -
Partial Discharge Inception Voltage of Voids Enclosed in Epoxy/Mica versus Voltage Frequency and Temperature
Aakre, Torstein Grav; Ildstad, Erling; Hvidsten, Sverre (Journal article; Peer reviewed, 2020)Detection of partial discharges (PDs) is widely used as a condition assessment tool for high voltage equipment. Application of low frequency test voltage is often preferred in the case of test objects with a large capacitance. ... -
Partial Discharges in Voids at Variable Voltage Frequency and Temperature Diagnostic Testing of Stator Mainwall Insulation
Aakre, Torstein Grav (Doctoral theses at NTNU;2020:143, Doctoral thesis, 2020)The main purpose of this thesis is to improve diagnostic testing by PD detection at variable voltage frequency by developing and experimentally testing theoretical models proposed for measurement of PDs in voids in a ... -
PD-Activity in Generator Stator Bar insulation versus Voltage Frequency and Temperature
Aakre, Torstein Grav; Ildstad, Erling (Chapter, 2020)Condition assessment of generators is today performed at various voltage frequencies and test temperatures. The main purpose of this paper is to compare measured PD results from sections of generator bars with that of ... -
Review of Partial Discharge and Dielectric Loss Tests for Hydropower Generator Bars
Aakre, Torstein Grav; Ildstad, Erling; Hvidsten, Sverre; Nysveen, Arne (Journal article; Peer reviewed, 2017)Condition assessment of hydropower generators is important to ensure high serviceability of power stations. Many of the in-service generators are old and current load operation schemes demands more than the design load, ... -
Time Development of Voltage Frequency Dependence of Partial Discharge Activity in Voids
Aakre, Torstein Grav; Ildstad, Erling; Hvidsten, Sverre (Journal article; Peer reviewed, 2019)Condition assessment of high voltage equipment based on partial discharge measurements is often performed after a voltage pre-conditioning period. The aim of this paper is to present results from experimental examinations ... -
Time to breakdown studies for liquids of different physico-chemical nature
Aakre, Torstein Grav; Lundgaard, Lars Esben; Unge, Mikael (Chapter; Peer reviewed, 2017)An automated setup for testing dielectric performance of liquids in a small point-to-plane gap is presented. It provides step voltages with rise times around 30 ns, with amplitudes up to 90 kV. Breakdown studies of thirteen ... -
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 ...