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The Effect of Partial Discharge Aging on the Dielectric Response of Polymers
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2014 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

This work investigated the effect of partial discharges (PD) on the complex permittivity

of PVC, PC, PTFE, PE and PA6. The material samples were subjected to prolonged

PD activity and the complex permittivity of the material was measured by dielectric

spectroscopy (DS) before and after the sample was aged. The results showed a change

in the loss factor for the tested materials, some were more affected than others and

showed different behaviors when subjected to the PD aging. Hence it was not possible

to find any general trend in the complex permittivity of the tested materials. Several

of the materials exhibited a loss factor with -1/2 slope at low frequencies corresponding

to diffusion. The -1/2 slope implies that the loss factor and the dynamic component of

the real permittivity should be equal, which could not be seen. Therefore it is uncertain

whether what was observed is a diffusion process or not. The results could suggest that

PD aging causes a change in the trapping characteristics of the material. Furthermore,

space charges deposited on the cavity wall from the PD activity could diffuse into the

bulk of the material where some of the charges are trapped. If a DS measurement

is performed before the trapped charges have had time to recombine or be conducted

away, it could affect the complex permittivity. This was demonstrated by performing

another DS measurement on an aged PC sample which had been left to rest for 35 days.

The measurement showed that the complex permittivity had returned to almost the

same state as before aging. Measurement problems were encountered which affected the

measurements in this work. The problems are believed to be caused by the measurement

electrodes used for the DS measurements not being heavy enough to eliminate small

unwanted air-gaps between the electrodes and sample. Furthermore, incomplete results

were obtained for some measurements which was believed to be due to the capacitance of

the sample being at the limit of what the measurement instrument was able to measure.

Abstract [sv]

Det här arbetet undersökte effekten av partiella urladdningar (PD) på den komplexa

permittiviteten i PVC, PC, PTFE, PE och PA6. Materialproverna utsattes för långvarig

PD aktivitet och materialets komplexa permittivitet mättes med hjälp av dielektrisk

spektroskopi (DS) före och efter att provet åldrats. Resultaten visade en förändring i

förlustfaktorn i de testade materialen, några påverkades mer än andra och de uppvisade

olika beteenden när de blev utsatta för PD åldring. Det var därför inte möjligt att hitta

någon generell trend i den komplexa permittiviteten för de olika testade materialen.

Flera av materialen uppvisade en förlustfaktor med -1/2 lutning vid låga frekvenser

vilket motsvarar diffusion. -1/2 lutningen medför att förlustfaktorn och den dynamiska

komponenten av den reella permittiviteten borde sammanfalla, vilket inte kunde ses.

Det är därför osäkert huruvida det som observerats är en diffusionsprocess eller inte.

Resultaten kan tyda på att PD-åldring orsakar en förändring i potentialfällors egenskaper

i materialet. Således skulle rymdladdningar som deponeras på väggarna i kaviteten på

grund av PD-aktiviteten kunna diffundera in i materialet där en del av laddningarna

fastnar. Om en DS mätning görs innan de fångade laddningarna har fått tillräcklig tid

att rekombinera eller ledas iväg, kan det påverka den komplexa permittiviteten. Detta

visades genom att genomföra en DS mätning på ett åldrat prov av PC som fått vila i

35 dagar. Mätningen visade att den komplexa permittiviteten hade återgått till nästan

samma tillstånd som innan den åldrades. Mätproblem påträffades vilket påverkade

mätningarna i detta arbete. Problemen antas vara orsakade av att mätelektroderna som

användes till DS mätningarna inte var tillräckligt tunga för att eliminera små oönskade

luftgap mellan elektroderna och provet. Dessutom erhölls ofullkomliga resultat för några

av mätningarna vilket tros bero på att provets kapacitans befann sig på gränsen för vad

mätinstrumentet kunde mäta.

Place, publisher, year, edition, pages
2014. , 75 p.
Series
EES Examensarbete / Master Thesis, XR-EE-ETK 2014:018
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-157323OAI: oai:DiVA.org:kth-157323DiVA: diva2:769750
Educational program
Master of Science in Engineering - Electrical Engineering; Master of Science - Electric Power Engineering
Examiners
Available from: 2014-12-09 Created: 2014-12-08 Last updated: 2014-12-09Bibliographically approved

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