Led by: Prof Manu Haddad, Cardiff University
One of the major challenges in power systems is the transport of bulk energy from generation to load points. The effective routing of this energy with cost efficient and environmentally-friendly infrastructure is highly desirable for the next generation of power networks and the upgrade of the ageing infrastructure. Current electricity transmission and distribution techniques include overhead lines and power cables. Whilst overhead lines are the cheapest option, they have the disadvantage of being visually undesirable and, hence, the significant opposition of the general public to new overhead lines. Power cables, on the other hand, are very attractive when buried or for undersea transmission, but they are about 20 times more expensive. For long offshore routes, over 80km, HVDC cables are required due to limitations in power transfer capabilities of ac cables. Such HVDC have a further cost attached to them and a limitation in power transfer and life expectancy.
For these reason, gas insulated lines operating with alternating voltage are being investigation as a possible future solution for both onshore and offshore transmission/distribution lines. The current insulation gas, used in gas insulated substations, equipment and lines, is SF6 gas. SF6 insulation gas has excellent dielectric properties allowing compaction of electrical equipment and space saving but the gas is highly damaging to the environment, having a global Warming Potential, GWP of 24000.
New more environmentally-friendly gas mixtures, based on CF3I gas having a GWP of less than 5, are being researched at Cardiff University. This is now being trialled in power systems equipment for insulation purposes.
This projects aims to investigate the properties of the new gas and its mixtures and determine its interaction with other materials. Gas Insulated bus bars, equipment and lines will be developed and tested using these new gas mixtures. The investigation will include analytical and experimental determination of various parameters and, thus, determine the suitability of the proposed gas for future deployment in electrical networks. If successful, it is envisaged that a demonstrator will be completed towards the end of the project. This has potential to open new research and industrial opportunities.
Work in this area was started at Cardiff University some 6 years ago with initial funding from National Grid for a feasibility study into CF3I gas as an insulation medium for SF6. Since then, three PhD studentships were won from the Power Network Research Academy (PNRA), The EPSRC Grand challenge “Top and Tail”, National Grid iCase award. Furthermore, two independently-funded PhD students have successfully completed preliminary research in this area. Currently, a one year research project is funded by EPSRC to build a short length gas insulated line with significant equipment support from National Grid. PNRA has also approved a short grant to extend the PhD research programme and investigate breakdown by-products. Significant research collaboration is already on-going with the University of Tokyo in this area.
This work package proposes to investigate the fundamental properties of the new insulation gas and application to electrical power networks. The contribution to the consortium will focus on research related to CF3I gas and its mixtures as potential replacement for SF6 gas. We propose to investigate the basic properties of the gas including its long term performance and interaction with other materials within high voltage plant such as circuit breakers and gas insulated bus bars or lines. We will also explore ways of improving aspects of the gas properties, such boiling temperature, iodine absorption and better arc extension properties. It is intended that the 5-year project will explore basic characterization and modelling as well as applications to electrical power systems equipment/insulation. Work will be focused on design and application of circuit breakers and gas insulated lines aiming to develop working demonstrators ready to trialling on the electrical network.
The work package will:
a) Investigate properties of CF3I gas and its mixtures.
b) Determine interaction of CF3I Gas with other materials
c) Assess long term effect of gas and its by-products on other materials
d) Improve absorption of unwanted breakdown products and develop techniques to remove them from enclosed power equipment.
e) Develop demonstrator of circuit breaker and gas insulated lines with monitoring sensors.