Reflection on two decades of research in the fields of Gas Insulated Switchgear (GIS)
Speaker: Dr. Shawn Nielsen
When: 2009-07-13 11:00:00
Venue: 78-420
Host: Tapan Saha
Abstract:The diagnostics of Gas Insulated Switchgear (GIS) is important for insuring continued availability of the equipment. Due to the totally enclosed nature of GIS, novel diagnostic techniques need to be developed. There are three main diagnostic techniques available for GIS, some can be applied on-line and others are only suited to off-line testing. Partial discharge detection is recognised as an important diagnostic tool for GIS. This presentation will look at some of the work done particularly on electrical partial discharge detection in GIS. Due to space charge formation under power frequency excitation, the discharge activity associated with a defect will be reduced. This will result in a reduced detection sensitivity for the defect in question. In order to reduce the effects of space charge, partial discharge detection can be done under lightning impulse excitation. This work will look at some of the fundamental research done on the characterisation of discharges in SF6 under impulse excitation.
SF6 is primarily used in high voltage equipment as an arc interrupting medium as well as an insulating medium. SF6 has resulted in significant compaction of high voltage equipment due to its high dielectric strength. SF6 is unfortunately one of the most potent green house gasses known to man, with a Global Warming Potential of approximately 29 000. SF6 however has an accumulative effect due to its chemical stability unlike other gasses that eventual breakdown in the atmosphere. This presentation will look at some of the work done in developing tools for minimizing SF6 release into the atmosphere. The high absorption of Infra-red radiation in the 10.5 mm band by SF6 can be used to image SF6 emissions from high voltage equipment. Numerous optical techniques are available for the detection of rouge gases in the atmosphere. Background scattering absorption detection is a particularly cost effective technique for GIS.
Electric field modelling has become an almost indispensable tool for the design of high voltage equipment and the investigation of high voltage phenomena. Some examples of the use of electric field modelling will be given. Modelling can be used to achieve an optimal design of high voltage electrode geometries. Field modelling was used to reduce the audible noise from an existing 400 kV tri-Wolf bundled conductor. Two approaches were investigated. The first involved the optimum placement of two sub-conductors to reduce the operating electric field on all five conductors. The second approach was to find the optimum geometry by moving one of the three conductors in the original geometry to reduce the overall electric field on all three conductors. Field modelling was used to determine the corona onset on Adlash fibre attached to the shield wires of 400 kV and 765 kV transmission lines. The results were verified experimentally in the laboratory. Encapsulation of a vacuum interrupter(VI) in epoxy can form an effective bases for the design of high voltage switchgear. In order to reduce the size of switchgear, an earthed screen can be applied to the outside of the epoxy encapsulation. Electric field modelling was used to determine the effect of the earthed shielding on the lightning impulse performance of the open VI. This work shows that shields and in some cases also a semi-conducting layer is needed to improve the BIL performance of the open VI. Field modelling can be used to design the optimal placement of the needed shields.
Biography:Dr Shawn Nielsen was born in South Africa in 1967. He graduated from the University of the Witwatersrand with a BSc in Electrical Engineering in 1990. He was subsequently employed at the University of the Witwatersrand as a Professional Assistant to Prof Jan Reynders and Prof Ian Jandrell while conducting research towards his PhD. He was later employed as a Junior Research Officer while completing his PhD. In 2001 he went to work in the research arm of Eskom; the state owned electrical utility in South Africa; initially as a Senior Engineer and later as a Chief Consultant. Shawn graduated from the University of the Witwatersrand with a PhD in Engineering in 2002. The subject of his thesis was the detection of partial discharge activity in SF6 under impulse voltage excitation. At Eskom he conducted research on condition monitoring of Gas Insulated Switchgear, SF6 and its associated technologies as well as Electric Field Modelling. In 2006 he took up a position with a large manufacturer of medium voltage automatic pole mount reclosers in Brisbane as a Medium Voltage Technology Specialist. His current research activities are geared towards outdoor recloser architecture and dielectric material selection for new product development.
Type: Job Applicant seminar
Contact:Tapan Saha