Figure 1: a) Examples of electrical treeing in polyethylene from a thin tungsten wire. b) Surface discharges from a brass electrode emitting light.

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1 Tittel: Delutladninger og elektrisk trevekst i elektriske isolermaterialer for undervanns installasjoner Title (eng): Degradation of Subsea Electrical Insulation Materials by Partial Discharges and Electrical Treeing Some electrical materials (as PTFE, FEP, PEEK etc.) have shown to be able to resist harsh environment combined with high temperatures, mainly due to the strong bonding between e.g. the carbon and fluor atoms. Therefore, such polymers are also attractive as high voltage insulation materials for different components used in subsea and oil installations. In such components also high electrical stresses can come into action. The main purpose of this project is to develop a new test setup for examine the resistance for the insulation materials to electrical treeing. It is also relevant to develop tools for manufacturing of suitable test samples. Electrical treeing has in high voltage cable insulation been studied widely as it is one of the major breakdown mechanisms for solid dielectrics subjected to high electrical stresses. A new type of electrode configuration will be examined which consist of a thin tungsten wire as electrode to obtain the high divergent electrical stress needed to initiate electrical trees. This allows for determining the tree initiation field and the rate of tree growth. It should be possible to subject different environments to the test samples, such as e.g. humidity, temperature and type of gases. It is also relevant to study another path to electrical tree formation - the application of surface discharges causing oxidation and erosion. Figure 1: a) Examples of electrical treeing in polyethylene from a thin tungsten wire. b) Surface discharges from a brass electrode emitting light. It is feasible to continue the study within the Master Thesis work (e.g. to include a light sensitive CCD camera to monitor the growth rate and eventually the emitting light during the process). Also summer job at SINTEF Energy Research is possible. The work will be mainly experimental. SINTEF project financed by Norwegian oil industry and companies, and the Norwegian Research Council. Kontaktinfo (SINTEF Energi) Oddgeir Kvien (Oddgeir.Kvien@sintef.no), Gunnar Berg (Gunnar.Berg@sintef.no),

2 Tittel: Mekanisme for dannelse av vanntrær i mellomspenningskabler Title: (eng): Mechanism for Initiation of Vented Water Trees in Medium Voltage XLPE Cables Water treeing is considered the most important failure mechanism for medium voltage cables in service. Water trees grow in the electrically stressed (3-5 MV/m) insulation at a high relative humidity and from contaminants. It takes typically from 5 to 30 years before an electric breakdown of the insulation occurs due to the trees. Lately it has been discovered that corrosion of the aluminium conductor in the cable causes environmental stress cracking of the semi-conductive conductor screen and further void/channel growth to the insulation where vented water trees then can start to grow. In this project work, further study of this mechanism will be examined. High voltage XLPE cables is now being subjected to accelerated ageing in the laboratory, where the effect of different service conditions is systematically studied (e.g. mechanical stress of the conductor screen, type of liquid in the conductor, temperature (uniform/gradient), voltage stress). The aged cables are planned to be characterised by partial discharge measurements for localisation of any water trees and microscopy (e.g. Scanning Electron Microscopy - SEM) analysis of the insulation. a) b) c) d) Figure 1: a) Structures/channels in the conductor screen causing severe water treeing. b) SEM picture within the bulk of the water tree region (located at the white arrow). c) Hollow structure with a direction into the XLPE insulation situated at the interface between the conductor screen and the insulation (note the network of fibrils). d) Micro-crack at the inner surface of the conductor screen. It is feasible to continue the study within a Master Thesis work. Also summer job at SINTEF Energy Research is possible. The work will be supported by a SINTEF project financed by Norwegian industry and the Norwegian Research Council. Kontaktinfo SINTEF Energi: Hallvard Faremo (Hallvard.Faremo@sintef.no),

3 Title: Diffusion of Water in Filled High Voltage Cable Materials at High Hydrostatic Pressures Tittel: Diffusion av vann i fylte kabelmaterialer ved høye hydrostatiske trykk The lifetime of power cables without metallic barriers in humid environments is limited by degradation by water tree growth from contaminations in the cable insulation. The water content in the insulation is one of the key factors determining the rate and degree of water tree growth, and it is therefore of great importance to be able to predict the rate and amount of water uptake in commercially available polymeric cable materials under different environmental conditions. Although it is, in principle, easy to model the water uptake in polymers, there are several factors that complicate the process due to the vast number of different commercially available plastics. These factors include the presence of fillers and/or micro pores in the material, which are essential to understand in order to characterize the available cable insulation materials with regard to water transport. a) b) c) d) Figure 1: a) 500 bars 150 o C pressure vessel for diffusion experiments. b) Subsea high voltage XLPE cable. c) Polymer (outer sheath of the cable) filled with carbon black. d) Water trees in the cable insulation. The main purpose of the project will be to establish a procedure for measuring (sea-) water diffusion in filled materials at different temperatures and hydrostatic pressures. Scanning electron microscopy (SEM) will be used for morphological characterization of the materials. The water transport properties of the samples will be characterized by different techniques (such as the freeze drying method or microweighing). It is possible to continue the study with a Master s Thesis during the spring of One possible approach is to establish a numerical or analytical model that can be used as a basis for predicting the water transport in polymers at different hydrostatic pressures and temperatures. The student project and master work will be a part of a large project funded by the Norwegian Research Council and Norwegian utilities and cable industry. The candidate will also be offered a summer job at SINTEF Energy Research during the summer Kontaktinfo: Svein Magne Hellesø (Svein.Helleso@sintef.no) Tlf: Sverre Hvidsten (Sverre.Hvidsten@sintef.no) Tlf:

4 Tittel: Elektrisk isolasjon for turbiner for offshore vindmøller Title (eng): Electrical Hybrid Insulation for Offshore Wind Turbines Today there is a driving force to develop new types of wind turbines and floating towers for deep water deployment offshore. In order to keep a low weight of the turbines, they consist to a large extent of polymeric materials. This also includes the electrical insulation and protecting parts of the design. For some machines, the insulation system is of a hybrid type, with both oil and solid insulation where the oil is being heated by the stator windings (cooling oil). The main purpose of this project is to examine the possible occurrence of surface discharges of the epoxy insulation material during service. This will be studied at different temperatures, wetting and electrical conductivity. In addition, the cooling oil can in service diffuse to the surface of the epoxy and (possibly) limit the surface degradation. An experimental set-up will be designed, built and tested in the project work. a) b) Figure: a) Discharges tracking across the surface of a polythene sheet. b) Floating offshore wind turbines The project work will be included in a long term project at SINTEF Energy Research funded by SmartMotor AS. A summer job in 2010 at SmartMotor AS is possible (also partly located in the laboratories at SINTEF Energy Research). This work will also be very applicable for Master work in 2011 including development of concepts for surface modifications. Kontaktinfo (SINTEF Energi): Odd Lillevik (odd.lillevik@sintef.no), (SmartMotor): Pål Keim Olsen (pal@smartmotor.no), SmartMotor AS, +47

5 Tittel: Dielektriske egenskaper til en nanokompositt Tittel (eng): Dielectric Properties of an Epoxy Nanocomposite Nanocomposites represent a radical alternative to conventional insulation systems where particles that have been added to reinforce the polymer are in the micrometer range. The use of nanocomposites has shown that the electrical and mechanical properties are significantly improved compare to conventional systems. For example Amine modified Polyhedral oligomeric silsquioxane (amine-poss) have previously been used to modify sodium montmorillonite (MMT) nanoclays for improved dispersion in epoxy resin. The introduction of the amine-poss was found to have a positive effect on the dispersion of the MMT clays and prevented agglomeration. Moisture has been considered the most important degradation factor for many composites with inorganic fillers. Water can cause swelling and also attack the cross-linking between the fillers and the resin and therefore make the polymer mechanically weaker. The main purpose of this student work is to examine the performance (electrical/mechanical) of a nanocomposite epoxy in humid environment. This includes measurements of the dielectric response (complex permittivity) in frequency domain as well as the electrical conductivity at different temperatures, relative humidity, frequencies and electrical stresses. Also the long term performance (ageing) is also considered including mechanical measurements. It is feasible to continue the study within a Master Thesis work. Also summer job at SINTEF Energy Research is possible. The work will be performed within a SINTEF project financed by Norwegian oil industry and companies, and the Norwegian Research Council. Figure 1. Chemical structure of the POSS-NH 2 monomer. Kontaktinfo (SINTEF Energi): Hans Helmer Sæternes (Hans.H.Saternes@sintef.no)