| 1. |
- Edvall, Martin, et al.
(author)
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Experimental study of current damages in bearings
- 2007
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In: Proceedings of the Third International Conference on Advances in Processing, Testing and Application of Dielectric Materials. - 0324-9441. ; , s. 141-146
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Conference paper (other academic/artistic)
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| 2. |
- Jarvid, Markus, 1985, et al.
(author)
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Evaluation of the Performance of Several Object Types for Electrical Treeing Experiments
- 2013
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In: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 20:5, s. 1712-1719
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Journal article (peer-reviewed)abstract
- A comparison of the efficiency of various types of object for studying the development of electrical trees in polymers is presented. Two types of newly developed wire-plane objects are investigated and compared with two versions of the traditionally used needle-needle objects. The two needle-needle objects are prepared according to ASTM standard and act as references, whereas the alternative objects rely on use of an ultra-thin tungsten wire (10 and 20 µm) in the test objects for providing the highly divergent electric stress. In one type of those object the wire extends from a semiconducting tab embedded in the tested material, while in the other type, the embedded wire is extended and connected externally by means of a copper tape. The comparison is made using cross linked polyethylene (XLPE) for the testing purposes. The wire type objects provide some promising advantages, including parallel formation of several electrical trees and an exposure of a larger material volume. Further advantages include the considerable simplification of both the manufacturing and the measuring procedures. Among the newly developed test objects, the one without the semiconducting tab is considered most advantageous as it allows for more accurate treeing initiation measurements at a lower voltage level. On the other hand the disadvantage is a formation of kinks on the wire that results from polyethylene shrink during sample preparation, which may yield some difficulties in correctly estimating the local field strength locally as well as straining the surrounding material. However the multitude of electric trees formed in each sample allows to easily discard the trees growing at such imperfections in following data analyses. Although finding a statistical method that makes good use of all the data poses a challenge, a suggested approach is presented.
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| 3. |
- Johansson, Anette, 1977, et al.
(author)
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A Versatile System for Electrical Treeing Tests under AC and DC Stress Using Wire Electrodes
- 2011
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In: 8th International Conference on Insulated Power Cables, Jicable’11, 19 – 23 June 2011, Versailles - France.
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Conference paper (other academic/artistic)abstract
- An alternative method to evaluate electrical treeing in solid dielectric materials is presented. Here the test sample utilises a wire electrode for creating the necessary high divergent electric field. This introduces a different preparation method and several of the disadvantages with the traditional needle sample can be avoided. Together with the test object a versatile test setup for both AC and DC measurements is illustrated. This alternative method has proven successful and an evaluation thereof as well as a comparative study between the two electrode systems is included.
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| 4. |
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| 5. |
- Bergman, Becky, 1970, et al.
(author)
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Reflections on an Integrated Content and Language Project-Based Design of a Technical Communication Course for Electrical Engineering Students.
- 2013
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In: Journal of Academic Writing. - 2225-8973. ; 3:1, s. 1-14
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Journal article (peer-reviewed)abstract
- Effective ways of teaching technical communication skills to engineering students have been much discussed. This article reflects on one setting, a first year course in Technical Communication at a university in Sweden, where electrical engineering teachers, language and communication teachers and student counsellors work in close, team-based cooperation using a project model which requires the students to analyse, implement and communicate technical problems. The paper discusses the change in this course - from an EAP course primarily prioritizing language training which ran parallel with a project course - to one unified ICL course. The progression is described through the changes in the organization of the course, and the article focuses on one learning activity: interdisciplinary tutorials on project reports. Through a pilot study where these sessions were video recorded and mapped, we conclude that the presence of different roles became an asset for the range of what the students see as relevant for their project report. In particular, the technical report genre was critically analysed, including problematic areas such as textual sequencing and display of technical problems; data visualisation and commentary; and referencing.
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| 6. |
- Bernelo, Marie, 1958, et al.
(author)
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May an Increased Focus on Students’ Personal Development Contribute to Increased Motivation, Better Academic Performance and Teamwork in Engineering Programs?
- 2011
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In: Proceedings of 7th International CDIO Conference, Copenhagen, Denmark.
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Conference paper (peer-reviewed)abstract
- Our hypothesis is that an increased focus on engineering students’ personal development in the curricula will increase their motivation, academic performance and teamwork. With this starting point we have developed the EDIT model for personal development aimed at the engineering students in the 5-year EE, CE and SE programs at Chalmers University of Technology. The EDIT model comprises the topics and the process and timing of the delivery in the curricula at the bachelor level. It is based on behavior-scientific theories and on 40 years of experience in guiding engineering students at Chalmers. The fundamental concept for the model is that introspective knowledge gives extrovert ability. It comprises four topics: Motivation and learning, Teamwork, Leadership, Career and professional life, and a complementary reflection package. Based on motivational theory and pedagogical literature, we discuss why we have selected these topics and how they should be implemented in the curricula and syllabi to facilitate the development of the students. We argue that these topics should be placed in a context and at a time that makes them meaningful to the students. We give practical examples from the project test implementation and discuss practical issues that are likely to hinder the long-term success. In conclusion, we find that there is some evidence from our experiments that motivation and teamwork is improved. The possible effect on academic performance is so far very hard to assess.
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| 7. |
- Blennow, Jörgen, 1966, et al.
(author)
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Active High Voltage Insulation
- 2002
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In: Journal of Electrostatics. ; 55:2, s. 159-172
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Journal article (peer-reviewed)
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| 8. |
- Blennow, Jörgen, 1966
(author)
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Active High Voltage Insulation - A New Hybrid Insulation Concept with Dynamic and Active Features
- 2000
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Doctoral thesis (other academic/artistic)abstract
- In this thesis, the concept of a new environmental-friendly and high-performance high voltage insulation is presented. Basically, it is an electric field steering technique where the dynamic process of charge accumulation, actively and advantageously, re-distributes the electric field within an insulation system. The concept is theoretically and experimentally demonstrated on a one-dimensional plane-parallel insulating structure consisting of an air-gap bounded by two dielectrically covered electrodes. The vital process of charge deposition and relaxation was experimentally studied in a highly lightning impulse (LI) voltage stressed air-gap. The temporal and spatial development of dielectric barrier discharges, studied through current measurements correlated with sequential high speed imaging, revealed fundamental properties of the highly stressed system. In general, an intense discharge was found at the front of the LI followed by a pulse train of significantly smaller discharges, but of opposite polarity, at the tail of the LI. During both a slowly rising dc-voltage and during a sequence of LI- voltages; voltage levels remarkably above the level which, according to the capacitive field distribution gives critical field strength in the air-gap, were reached. The improvements ranged from about 50% for a 27 mm dc-stressed gap, up to 350% for a 3 mm LI-stressed gap. Actual maximum withstand levels were not reached. It can be concluded that a significant feature is that the system adapts its insulation level with respect to what the applied voltage level requires by an accumulation of the appropriate quantity of charge. If the demand of charge exceeds the supply, additional free charge is automatically created through ionization. Although, ionization is not a pre-requisite behind the concept. Under ideal conditions, such a system will in equilibrium exhibit a zero air-gap field, e.g., the electric breakdown strength is only determined by the coatings. Thereby, the breakdown strength could be considerably improved in comparison with a conventional uncovered air-gap.
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| 9. |
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| 10. |
- Blennow, Jörgen, 1966, et al.
(author)
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Comparative study of dielectric spectroscopy measurements and anayses of oil and paper samples from a transformer undergoing repair
- 2005
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In: In Proc. of 19th Nordic Insulation Symposium, Trondheim, Norway, June 13-15.
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Conference paper (other academic/artistic)abstract
- New methods, based on characterisation of dielectric response measurements, for assessing moisture content of pressboard and paper are gaining ground. However, there is a need for calibrating results with results from other techniques. This communication presents results from a study of a 19.5/6.8/6.8 kV - 40 MVA power transformer, which was opened on-site during maintenance work, thus allowing for collecting paper samples. Dielectric spectroscopy measurements were conducted before and after its opening. Results were compared with measurements on oil and paper samples. These showed that the moisture levels in the interior of the solid insulation were unchanged. Further, it was found that FDS measurements gave more accurate estimates of moisture levels than estimates based on oil analyses and equilibrium curves.
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