Non-destructive testing of capless porcelain line post insulators to detect internal defects

Borrill, Leslie (Leslie David) (2003-12)

Thesis (MScEng)--University of Stellenbosch, 2003.

Thesis

ENGLISH ABSTRACT: This project relates to the unexplained failure of 33kV porcelain line post insulators in ESKOM's Southern Region. An initial investigation suggested that the failures could probably be due to a combination of internal manufacturing flaws and the effects of lightning. The failures all occurred in insulators based on a new design that uses a metal spindle for mechanical attachment to a power line structure embedded in the insulator base. This thesis investigates the non-destructive detection of internal flaws in porcelain line post insulators. The research was structured as follows: • The examination of the manufacturing process and materials used to determine the cause, location and nature of internal flaws. • An electrical field simulation study to verify whether a void in the sulphur cement will experience discharge activity when exposed to systeni nominal voltage or lightning potential. • The identification of non-destructive techniques (NDT) that are potentially viable for determining the presence of insulator internal flaws. • The design of NDT experiments for X-ray, partial discharge (PD) detection and ultrasonic testing. These experiments were evaluated for their effectiveness in determining the presence of internal flaws and their usefulness as a quality control measure in the insulator manufacturing process. The main findings are: The major cause of insulator internal flaws is the fast setting sulphur cement used for cementing the metal spindle (mechanical attachment) to the porcelain body of the insulator. The field simulation study shows that a discharge in a 3mm diameter spherical void on the insulator's axis of symmetry will occur if the insulator is exposed to lightning potential. High energy X-raying is an effective technique for exposing the location, nature, size and number of flaws in the insulator, but is impractical due to the high Xraying cost and over-utilisation of the only high energy X-ray facility in the RSA. The PD experiment was effective in revealing the presence of internal flaws, but the location, nature, size and number of flaws cannot be determined. The experiment is time consuming and is therefore not suitable for quality control in the insulator manufacturing process. A preliminary investigation into the suitability of ultrasonic testing techniques encountered major technical difficulties. Further investigation into the use of ultrasonic 3D imaging techniques is recommended.

AFRIKAANSE OPSOMMING: Hierdie projek hou verband met die onverklaarbare faling van 33kV porselein staaftipe isolators in ESKOM se Suidelike Streek. 'n Aanvanklike ondersoek het daarop gedui dat die falings veroorsaak is deur 'n kombinasie van interne vervaardigingsfoute en die effek van weerlig. Die falings het almal plaasgeving op isolators waarvan die vashegtingsbout direk in die porselein versink is. Die doel van hierdie navorsingsprojek is om nie-vernietigende toetsmetodes (NVT) te ondersoek, teneinde interne foute in die tipe isolators op te spoor. Die tesis is soos volg gestruktureer: • Die ondersoek van die vervaardigingsproses en die materiale wat gebruik word, ten einde die oorsaak, posisie en aard van hierdie foute vas te stel. • 'n Simulasie van die elektriese veld om vas te stelof 'n holte in die swaelsement ontladings salondervind onder die invloed van nominale spanning en weerlig. • Die indentifisering van nie-vernietignde toetsmetodes wat gebruik kan word om die teenwoordigheid van interne foute te bepaal. • Die ontwerp van NVT eksperimente vir X-straal, gedeeltelike ontlading ("PD") deteksie en ultrasoniese toetsing. Hierdie eksperimente is geëvalueer om hul effektiwiteit om die teenwoordigheid van interne foute vas te stel, asook hul nuttigheid as 'n kwaliteitsbeheermaatreël in die iso latorvervaardigingsproses. Die hoofbevindinge is: Die hoofoorsaak van die interne foute is die vinnig-stollende swael-sement wat gebruik word om die metaalinsetsel aan die porselein te heg. Die veldsimulasies het getoon dat 'n ontlading in 'n 3mm sferiese holte op die isolator se simmetrie-as sal plaasvind as die isolator aan weerligpotensiaal onderwerp word. Hoë-energie-X-strale is 'n effektiewe tegniek om die posisie, aard, grootte en aantal foute in die isolator vas te stel. Dit is egter onprakties as gevolg van die hoë koste en oorbenutting van die enigste hoë-energie-X-straal-fasiliteit in die RSA. Die ontladingsdeteksie eksperiment was effektief om die teenwoordigheid van interne foute aan te dui, maar die posisie, aard; grootte en getal foute kan nie bepaal word nie. Die eksperiment is tydrowend en is daarom nie geskik vir kwaliteitsbeheer van die isolatorvervaardigingsproses nie. 'n Voorlopige ondersoek na die geskiktheid van ultrasoniese toetsmetodes het groot tegniese stuikelblokke opgelewer. Verdere ondersoek van die gebruik van ultrasoniese 3D-beeldtegnieke word aanbeveel.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/53525
This item appears in the following collections: