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Torstein Grav Aakre

Research Scientist

Torstein Grav Aakre

Research Scientist

Torstein Grav Aakre
Phone: 915 48 964
Department: Electric Power Technology
Office: Trondheim

Publications and responsibilities

Publication
https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1714968

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 of time variance of partial discharge activity and to propose physical explana...

Authors Aakre Torstein Grav Ildstad Erling Hvidsten Sverre
Year 2019
Type Journal publication
Publication
https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1619732

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 assessment and monitoring of electrical machines. The main concern of using very lo...

Year 2018
Type Part of a book/report
Publication
https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1619730

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 and samples were taken after 35 years in service from both the low and high vol...

Authors Aakre Torstein Grav Ildstad Erling Hvidsten Sverre
Year 2018
Type Part of a book/report
Publication
https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1526045

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 different liquids were conducted with a gap distance of 4 mm in a test cell ...

Year 2017
Type Part of a book/report
Publication
https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1394037

Knowledge of the conductivity and permittivity of materials used in subsea connectors is needed to predict the electric field distribution in the connectors. The synthetic ester Midel 7131, being one of several dielectric liquids used in subsea connectors, has been chosen as a relevant candidate mat...

Year 2016
Type Journal publication
Publication
https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1375207

Polypropylenes (PP) are a candidate to replace cross-linked polyethylene (XLPE) in medium voltage cables. This is due to its recyclability and potentially lower energy consumption during production. To prove to be an alternative, the PPs must meet the same requirements as for XLPE. The maximum servi...

Year 2016
Type Part of a book/report
Publication
https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1162812

A numerical 3D simulation of positive streamer propagation in a liquid, using cyclohexane as a reference case, in a needle-plane geometry is presented. The physical basis of this model is a version of the Townsend-Meek streamer criteria, known from gas discharges, adapted to a liquid containing an a...

Authors Hestad Øystein Leif Grav Torstein Lundgaard Lars Esben Ingebrigtsen Stian Unge M. Hjortstam O.
Year 2014
Type Part of a book/report
Publication
https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1162810

Partial discharge (PD) measurement in a needle to plane gap is suggested by IEC used for ranking dielectric liquids. This paper investigates PD behavior in eight liquids using a 20 mm ac stressed needle to plane gap. Parameters varied were tip radius, frequency and voltage. Both discharge phase dist...

Year 2014
Type Part of a book/report
Publication
https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1162808

Currents and space charge phenomena in 8 different dielectric liquids have been investigated for an ac stressed needle plane gap. Applied frequencies ranged from 0.1 Hz to 100 Hz. A high resolution analogue-digital converter and an active suppression of capacitive currents were used to extract the s...

Year 2014
Type Part of a book/report