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...

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...

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...

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 ...

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...

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...

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...

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...