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Aging of oil impregnated paper due to Pd activity
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. (High voltage group)ORCID iD: 0000-0003-1766-8077
Elektroteknisk teori och konstruktion, Electromagnetic Engineering. (High voltage group)
Elektroteknisk teori och konstruktion, Electromagnetic Engineering. (High voltage group)
Elektroteknisk teori och konstruktion, Electromagnetic Engineering. (High voltage group)
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2013 (English)Conference paper, Published paper (Other (popular science, discussion, etc.))
Abstract [en]

Air filled cavity may appear inside solid insulation either due to bad manufacturing or as a result of insulation ageing. A cavity is a weak point in insulation and if the electric stress is high enough; partial discharge can be initiated inside the cavity. In this paper changing of PD parameters (number of PD, maximum magnitude of PD and average magnitude of PD) was investigated over time on oil impregnated paper with an artificial cavity in between the sheets of paper. PD parameters were recorded from the inception of PD until final puncture breakdown occurs in the sample. Experiment was performed on sample with different thickness. Specific pattern on changing of PD number and maximum magnitude of PD was observed for most of the experiments. The pattern includes three stages, big discharges appear at inception of PD and over a very short time they disappear. At stage two, the number and magnitude of PD increase rapidly from small values until they reach to a maximum value. At stage three, the number and magnitude of PD decreases and reach to a constant value. The PD parameter keep constant until the time that final breakdown occurs. The dielectric spectroscopy performed on the sample before and after exposure to PD shows that PD activity causes a permanent shift on ε" which can be explained by PD by-products.

Place, publisher, year, edition, pages
2013.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-136428OAI: oai:DiVA.org:kth-136428DiVA: diva2:676099
Conference
18th International Symposium on High Voltage Engineering, August 25th-30th 2013, Seoul, South Korea
Note

QC 20131219

Available from: 2013-12-05 Created: 2013-12-05 Last updated: 2015-02-06Bibliographically approved
In thesis
1. Mechanisms of Electrical Ageing of Oilimpregnated Paper due to Partial Discharges
Open this publication in new window or tab >>Mechanisms of Electrical Ageing of Oilimpregnated Paper due to Partial Discharges
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, partial discharge (PD) phenomenon in oil-impregnated paper (OIP) is investigated under accelerated electrical stress. The thesis is mainly focused on the characteristic of PD activity and the influence it has on the insulation properties of OIP. PD source was created by introducing an air filled cavity embedded between layers of OIP. PD activity is investigated from the initiation up to final puncture breakdown of the OIP. The time-evolution of number, maximum magnitude and average magnitude of PD is investigated for cavities with different diameter and height. It was found that time to breakdown is shorter if the cavity diameter is larger and cavities with higher depth produce larger PDs. Comparison between PD activity in three cases, i.e. unaged OIP, thermally aged OIP and OIP samples with higher moisture content is performed. In general, it is found that for all cases the number and the maximum magnitude of PD follows a similar trend versus ageing time. During the very beginning of the experiment large discharges occur and they disappear after a short ageing time. Number and maximum magnitude of PD increase with time until reaching a peak value. Finally both parameters decrease with time and puncture breakdown occurs in the sample. Even though PD activity in thermally aged OIP is higher compared to the unaged OIP samples, the time to breakdown for new and thermally aged OIP samples is similar while it is shorter for OIP samples with higher moisture content.

In this thesis, partial discharge (PD) phenomenon in oil-impregnated paper (OIP) is investigated under accelerated electrical stress. The thesis is mainly focused on the characteristic of PD activity and the influence it has on the insulation properties of OIP. PD source was created by introducing an air filled cavity embedded between layers of OIP. PD activity is investigated from the initiation up to final puncture breakdown of the OIP. The time-evolution of number, maximum magnitude and average magnitude of PD is investigated for cavities with different diameter and height. It was found that time to breakdown is shorter if the cavity diameter is larger and cavities with higher depth produce larger PDs. Comparison between PD activity in three cases, i.e. unaged OIP, thermally aged OIP and OIP samples with higher moisture content is performed. In general, it is found that for all cases the number and the maximum magnitude of PD follows a similar trend versus ageing time. During the very beginning of the experiment large discharges occur and they disappear after a short ageing time. Number and maximum magnitude of PD increase with time until reaching a peak value. Finally both parameters decrease with time and puncture breakdown occurs in the sample. Even though PD activity in thermally aged OIP is higher compared to the unaged OIP samples, the time to breakdown for new and thermally aged OIP samples is similar while it is shorter for OIP samples with higher moisture content.

Breakdown strength of OIP samples is measured before and after ageing with PDs. It is found that the breakdown strength of OIP samples decreases by around 40% after the sample is exposed to accelerated electrical ageing. Furthermore a thermal model was developed to investigate the possible transition of breakdown mechanism from erosion to thermal breakdown in OIP dielectrics. It was found that PD activity can lower the thermal breakdown voltage of OIP up to four times.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xiv, 112 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2015:006
Keyword
partial discharges, oil-impregnated paper, oil, transformer insulation, dielectric frequency response, breakdown strength, ion mobility, thermal ageing, electrical ageing, moisture in paper, life time, thermal breakdown.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-159670 (URN)978-91-7595-443-1 (ISBN)
Public defence
2015-02-27, H1, Teknikringen 33, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Note

QC 20150206

Available from: 2015-02-06 Created: 2015-02-06 Last updated: 2015-10-08Bibliographically approved

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Ghaffarian Niasar, Mohamad

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