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ENERGIX-Stort program energi

Air Insulated Switchgear Technology

Awarded: NOK 11.0 mill.

Project Manager:

Project Number:

192918

Project Period:

2009 - 2014

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The project was carried out as a close collaboration between ABB Norway (Skien), SINTEF and NTNU. The main output of the project is a completely new, air insulated 12 kV ring main unit based on vacuum technology. The fundamental understanding of current interruption in air that was gained in this project now serves as a vital starting point for a new project (no 235284). A detailed summary of the main activities and results of the current project is given below: Current interruption Current interruption has been the main topic for both PhD students in this project. A dedicated laboratory has been constructed at NTNU and SINTEF. The fundamental principles of current interruption in air has been explored with extensive experimental studies. Key focus has been on a simplified puffer type switch and load current interruption test duties. Parameter variations were focused on geometry (contact and nozzle shapes, diameters, lengths etc), gas pressure/ velocity profiles and circuit parameters (current, voltage and time constants). In addition, ablation from polymer materials was investigated and found to improve the interruption capability significantly in designs where the polymer is placed close to the current arc. A deep understanding of test duties and international standards for type testing has been gained and several clarifications have been made. Several scale-up models relating current interruption ability to test duties and gas pressure have been developed and a predictive model based on statistical correlations in the accumulated experimental data has been prepared. Full scale experiments with existing SF6-based puffer switches were performed to evaluate their performance in air. It was found that puffer technology may indeed be used for interruption in air, but extensive re-design and optimization is required to make this into a cost effective product. The development of a puffer based load break switch was therefore postponed, and the first step in next generation SWG was therefore be based on vacuum interrupters for both power- and load current interruption. Fault current making In the first step of the product development, vacuum circuit breakers (VCB) have been chosen to also serve as load break switches, due to the limited current interruption properties of air. Commercially available VCB?s were therefore tested as load break switches in repeated making/breaking operations at load current conditions. The tests were successful and the VCB implemented in the final design of a new switchgear. Full scale testing and dielectric models were also used to ensure the fault making capacity of a new disconnector and earthing switch. Aluminium conductors Different alloys and casting processes were explored. The commercially available process of pressure die casting was found to be the most cost effective production method for main conductors. Literature surveys and experiments both showed that contact surfaces require silver coating to prevent oxidation and overheating. Detailed design was conducted and silver coated aluminium busbars (internal conductors) were developed as part of the final design Dielectric design Polymer coatings and dielectric barriers (screens) may be used to increase the insulation level in gas insulated SWG. Both fundamental- and product oriented experiments were carried out to explore different shapes and positions of dielectric barriers. These investigations revealed that insulating screens placed perpendicular to the field may in fact increase the insulation level significantly. However, care must be taken both in the design and installation of such screens, as even small gaps and openings may reduce their effect. Surface breakdowns along polymer/gas interfaces were explored with experiments. The insulation level of polymer/air interfaces parallel to the electric field were found to be largely unaffected by the type of polymer and to have little influence on the insulation level of the system. Major efforts were made to understand and predict the overall insulation level of the new design. Simulations and full scale experiments were undertaken in several loops to explore and optimize the dielectric withstand level of the final SWG. The main focus was given to the shape of the high potential conductors and reducing the maximum field strengths to accommodate for the reduce insulation level of air relative to SF6. Field controlling elements and the reduction of triple points secured the withstand level of the final product.

The customers of ABBs 12/24 kV metal enclosed switchgear units are continuously asking for technical improvements, more environmentally friendly solutions, lower prices, and at the same time unchanged physical dimensions. The project is essentially to d evelop the technology needed for future products to be able to comply with these demands. Four material related R&D tasks are addressed: 1) By rather fundamental experimental research - largely carried out as PhD-studies - the scientific and technologi al basis for a low cost, compact air interrupter for 24 kV / 630 A should be established. 2) A radically new conductor design for the switchgear should be developed and tested. The conductors will be hollow and made in aluminium, as opposed to existing s olid copper bar conductors. 3) New connectors and terminations for the aluminium conductors as well as new arcing and non-arcing contacts in switches and disconnectors will be developed. 4) A dielectric insulation system based on air instead of SF6 whic h is currently used, should be developed and tested.

Funding scheme:

ENERGIX-Stort program energi