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Thermoplastic field grading material for high voltage cable termination
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2011 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Termoplastiska fältstyrande material för högspänningsavslutningar (Swedish)
Abstract [en]

The purpose of this diploma work was to compound different field grading material by adding fillers (ZnO residue and carbon black) into two different polymers polyamide 6,6 and poly (butylenes terepthalate) (PBTP) and investigate the effect of filler concentration on mechanical and electrical properties. Three different concentration (15vol.%, 25vol.% and 30vol.%) of ZnO residue in combination with two different concentration (5vol.%, 10vol.%) of carbon black were mixed in into the polymer. The composites were compounded using a twin screw extruder and pellitizer.  Sheet samples for testing were prepared by compression moulding. The dielectric response, electrical breakdown strength and tensile properties were evaluated.

The dielectric response properties were tested in the frequency range of 0.01 Hz- 1 kHz and at 30, 60 and 90 °C. Filler concentration into the matrix increased the permittivity and loss factor. The highest permittivity and loss was obtained at low frequencies (f< 1 Hz), due to electrical conduction. At 30 °C, PBTP with 15vol.% ZnO and 5vol.% CB showed the minimum permittivity (12.9) and loss (0.19) at 46Hz. whereas corresponding PA composite showed lower permittivity 7.6 and loss 0.03.

The breakdown strength decreased with the addition of filler materials. PBTP composite having 15vol.% ZnO and 5vol.% CB showed the highest strength (16 kV/mm) among the PBTP composites, but it had lower strength than the corresponding PA 6,6 composite (21 kV/mm). Addition of black reduced the breakdown strength more than ZnO.

Addition of ZnO and CB increased the tensile strength of the material up to a certain concentration; 25% ZnO and 10% CB concentration showed the maximum strength (43 MPa) in PBTP composites. But with same composition the PA 6,6 composite showed higher tensile strength (67 MPa) than the PBTP composite (30 MPa). In elongation PBTP composite showed value (0.3%) which is 12.5% of elongation in PA 6,6 composite.

In conclusion the most promising formulation for field grading application is PA 6,6 filled with 15% ZnO and 5% CB, exhibiting a real permittivity of 7.6 and a dielectric loss of 0.03 at 46 Hz at 50C; electrical breakdown strength of 21 kV/mm, and tensile strength and elongation at break of 67 MPa and 0.4% respectively.

Place, publisher, year, edition, pages
2011. , 68 p.
Keyword [en]
Field grading material, Cable termination, ZnO varistor, Poly (butylenes terepthalate) or PBTP, Thermoplastic composite
National Category
Polymer Technologies
URN: urn:nbn:se:kth:diva-41486OAI: diva2:444133
Subject / course
Polymeric Materials
Educational program
Master of Science - Materials Science and Engineering
Physics, Chemistry, Mathematics
Available from: 2011-10-07 Created: 2011-09-27 Last updated: 2011-10-07Bibliographically approved

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