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Dielectric Response and Partial Discharge Diagnostics of Insulation Systems by Utilizing High Voltage Impulses
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, power system transients are considered as an opportunity for development of on-line diagnostics of power components and specifically the insulation systems of power transformers and bushings.

A new technique for on-line dielectric response measurement of power transformer bushings is proposed which utilizes natural transients in the power system, such as lightning and switching surges, as stimuli. Laboratory investigations are done on implementation of the proposed technique. Measurement considerations, data acquisition and processing involved in achievement of reasonable accuracy in the Dielectric Response (DR) are presented. Capability of the technique in tracking of the degradation signatures such as moisture content in the insulation has been evaluated and it has shown a good level of accuracy by being compared to the Frequency Domain Spectroscopy (FDS). 

The proposed technique is tested on the service-aged 150 kV bushings and feasibility of the technique for monitoring of dielectric properties of power transformer bushings has been assessed; the results are promising for the technique to be used in the real application. 

Partial Discharges (PD) behavior under transients has been also studied for different materials in this project. PD behavior of different defects, at different insulation condition, responding to the overvoltage transients in form of superimposed impulses on ac voltages was investigated and it was perceived how their distinctive response and the interpretation of  that, can be useful for their identification.

Besides the conventional materials, surface ac PD properties of modified paper with silica and zinc oxide nanoparticles under the superimposed impulses have been assessed in this project. Proper type and optimum concentration level of nanoparticles in the paper are the factors that lead to the improvement of PD behavior in the modified paper under overvoltage transients.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 79 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2016:080
Keyword [en]
Dielectric Response, Transients, Transformer bushing, Oil-impregnated paper, Moisture content, Partial discharge, Surface PD, Cavity PD, Superimposed impulse, Nanoparticles
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-187632ISBN: 978-91-7729-033-9 (print)OAI: oai:DiVA.org:kth-187632DiVA: diva2:930753
Public defence
2016-06-15, sal E3, Osquars backe 14, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20160525

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2016-06-16Bibliographically approved
List of papers
1. Dielectric Response Measurement with Impulse Stimulus on AC: Measurement Considerations, and Laboratory Testing on a Bushing
Open this publication in new window or tab >>Dielectric Response Measurement with Impulse Stimulus on AC: Measurement Considerations, and Laboratory Testing on a Bushing
(English)Manuscript (preprint) (Other academic)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-187626 (URN)
Note

QC 20160608

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2016-06-08Bibliographically approved
2. Dielectric Response of Oil-impregnated Paper by Utilizing Lightning and SwitchingTransients
Open this publication in new window or tab >>Dielectric Response of Oil-impregnated Paper by Utilizing Lightning and SwitchingTransients
2015 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 22, no 1, 335-344 p., 07033403Article in journal (Refereed) Published
Abstract [en]

On-line monitoring of insulation systems in power components such as power transformer bushings has significant value for their reliability. Dielectric spectroscopy is known as a powerful tool in condition assessment of power components' solid insulation. However, it is difficult to apply it on-line. Therefore, a new approach of intended use for on-line diagnosis of oil-impregnated paper, as a major insulation component of power transformers and bushings, is presented. In this technique, natural transients such as lightning and switching impulses are used as stimuli for on-line dielectric response measurements. The wide frequency range of these transients is their advantage as stimuli for dielectric spectroscopy. The influence of moisture content and temperature on the dielectric response of oil-impregnated paper has been investigated for performance evaluation of the proposed technique. It is shown that this technique can track the changes caused by moisture content and temperature in the dielectric response of oil-impregnated paper. The results of both low and high voltage study cases have been verified by comparison with Frequency Domain Spectroscopy (FDS). According to the well-matched results with FDS, the proposed technique can offer a valuable approach for frequent monitoring of dielectric properties of oil-impregnated paper insulated systems such as those commonly encountered in power transformer bushings. However, the validity range of the results depends on the bandwidth of the applied transients and other discussed measurement considerations.

Keyword
Dielectric response, high voltage impulses, moisture content, oilimpregnated paper, temperature, transients
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-144093 (URN)10.1109/TDEI.2014.004664 (DOI)000349776900040 ()2-s2.0-84923222442 (Scopus ID)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Note

QC 20150331

Available from: 2014-04-09 Created: 2014-04-09 Last updated: 2017-12-05Bibliographically approved
3. Insulation condition assessment of power transformer bushings by utilizing high voltage lightning impulses
Open this publication in new window or tab >>Insulation condition assessment of power transformer bushings by utilizing high voltage lightning impulses
2015 (English)In: 2015 IEEE Eindhoven PowerTech, PowerTech 2015, IEEE conference proceedings, 2015Conference paper, Published paper (Refereed)
Abstract [en]

High voltage bushing forms an essential part of a power transformer and its insulation condition is of high importance in a transformer's reliability. Transformer failure statistics indicate considerable contribution from bushing failures, which makes the monitoring of power transformer bushings essential. Several off-line and on-line methods are available for condition assessment of these components. However, most of the on-line methods cannot provide as much information as off-line methods because of the performance limitations. Therefore, condition assessments of these components are mostly done through several on-line methods and decision-making must be done according to majority agreements between different techniques. This paper investigates the possibility of assessing the insulation condition of power transformer bushing through utilizing high voltage transients. They are used as stimuli to get the dielectric response of the insulation system. The investigation is done on two service-aged 150 kV power transformer bushings. The results are verified by comparison with Frequency Domain Spectroscopy (FDS). The proposed application seems promising for monitoring of dielectric properties of power transformer bushings.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2015
Keyword
Dielectric response, lightning impulse, power transformer bushing, Decision making, Dielectric properties, Frequency domain analysis, Insulation, Lightning, Power transformers, Transients, Condition assessments, Frequency domain spectroscopy, High-voltage transients, Insulation conditions, Performance limitations, Transformer bushings, Bushings
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-181173 (URN)10.1109/PTC.2015.7232724 (DOI)000380546800491 ()2-s2.0-84951304792 (Scopus ID)9781479976935 (ISBN)
Conference
IEEE Eindhoven PowerTech, PowerTech 2015, 29 June 2015 through 2 July 2015
Note

QC 20160211

Available from: 2016-02-11 Created: 2016-01-29 Last updated: 2016-10-06Bibliographically approved
4. Effect of Superimposed Impulses on AC Partial Discharge Characteristics of Oil-Impregnated Paper
Open this publication in new window or tab >>Effect of Superimposed Impulses on AC Partial Discharge Characteristics of Oil-Impregnated Paper
(English)Manuscript (preprint) (Other academic)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-187627 (URN)
Note

QC 20160608

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2016-06-08Bibliographically approved
5. Effect of High Voltage Transients on Surface Discharge Characteristics of Oil-Paper Insulation
Open this publication in new window or tab >>Effect of High Voltage Transients on Surface Discharge Characteristics of Oil-Paper Insulation
2015 (English)In: 2015 IEEE Electrical Insulation Conference (EIC), IEEE , 2015, 69-72 p.Conference paper, Published paper (Refereed)
Abstract [en]

Condition assessment of power components such as power transformers and their bushings depends on the interpretation of data obtained from the monitoring systems. Various defects in their insulation would behave differently under electrical stresses. Surface discharge on the oil-paper interface is one of the defects which can be responsible for the failure of those components. Power system transients can impose stresses on the insulation of the power transformers and their bushings. This study investigates the effect of transients such as lightning impulses on the surface discharge characteristics of oil-impregnated paper. Two configurations, needle and rod (IEC-b), are used here. Two distinctive situations occur on paper due to these different configurations. The corresponding effect is shown in the form of variation in the partial discharge numbers and phase-resolved patterns. In the needle electrode configuration, the paper remains un-aged and the applied impulses cause a prompt change in the total number of discharges which decays fast. However, with the rod electrode, the paper gets carbonized and the applied impulses cause a decrease in the total number of discharges. The influence of moisture content in oil-impregnated paper was also studied. For this case, the total number of discharges considerably increase after applying impulse.

Place, publisher, year, edition, pages
IEEE, 2015
Keyword
oil-impregnated paper, surface discharge, impulse, PD pattern
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-184568 (URN)10.1109/ICACACT.2014.7223489 (DOI)000371481800014 ()2-s2.0-84978430407 (Scopus ID)978-1-4799-7354-5 (ISBN)
Conference
33rd IEEE Electrical Insulation Conference (EIC), JUN 07-10, 2015, Seattle, WA
Note

QC 20160405

Available from: 2016-04-05 Created: 2016-04-01 Last updated: 2016-05-25Bibliographically approved
6. Effect of High Voltage Impulses on Surface Discharge Characteristics of Polyethylene
Open this publication in new window or tab >>Effect of High Voltage Impulses on Surface Discharge Characteristics of Polyethylene
2015 (English)Conference paper, Published paper (Refereed)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-187629 (URN)
Conference
Nordic Insulation Symposium (Nord-IS)
Note

QC 20160608

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2016-06-08Bibliographically approved
7. Surface Discharge Characteristics of Oil-impregnated Paper with SiO2 and ZnO nanoparticles under AC with Superimposed Impulse
Open this publication in new window or tab >>Surface Discharge Characteristics of Oil-impregnated Paper with SiO2 and ZnO nanoparticles under AC with Superimposed Impulse
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-187628 (URN)
Note

QC 20160608

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2017-04-20Bibliographically approved

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