Abstract
Due to the ever-increasing demand for electricity in the one hand and the environmental constraints to use clean energy on the other hand, the global production of energy from remote renewable sources, particularly from large hydropower plants and offshore wind farms and their connection to the grid are expected to grow significantly in the future. Consequently, the demand to carry this electric power by high voltage direct current (HVDC) technology will increase too. The most suitable HVDC power transmission technology to deliver large amounts of power, exceeding a capacity of 5 GW per bipolar system over long distances with lower losses is by using compact HVDC gas insulated transmission lines (DC GIL) and gas insulated switchgears (DC GIS) with rated voltage (maximum continuous operating voltage) of ±550 kV and 5000 A which are presently under development worldwide. Among the critical challenges for the development of these HVDC gas insulated systems, there are the epoxy cast resin insulators that are used to separate gas compartments also called spacers. Indeed, thorough research studies have been and still being carried out to well understand and clarify the electrical insulation characteristics of HVDC spacers using mainly cylindrical samples and small insulator models, where useful results have been obtained and proposed for implementation in real compact gas insulated systems. However, few practical investigations have been undertaken on real size spacers (product scale) to verify such research outcomes and validate the reliability of the spacers to collect experiences or for commercial use. This paper reviews the current achievements of real size HVDC spacers development. It describes the basic electric field calculation and spacers design, the verification of the insulation performance and validation testing. It gives today’s commercially available compact HVDC GIS/GIL and finally it presents the envisaged future research and development.
Highlights
While for high voltage alternating current (HVAC) applications, gas insulated switchgears (GIS)and gas insulated transmission lines (GIL) are well-proven technologies operating under a voltage of at least 800 kV AC, their development for high voltage direct current (HVDC) applications is extremely challenging
Gas insulated transmission lines (GIL) are well-proven technologies operating under a voltage of at least 800 kV AC, their development for high voltage direct current (HVDC) applications is extremely challenging
Regardless the employed calculation method (Section 3.1.1 or Section 3.1.2), the most relevant results of the electric field distribution along full-size spacers performed under different operating conditions of the HVDC GIS/GIL: transient, DC steady state, DC polarity reversal and superimposed lightning/switching impulse voltages on DC pre-stress with and without load [11,12,35,36,37,38,39,40,41,42,43,44,45,46], are summarized as follows:
Summary
While for high voltage alternating current (HVAC) applications, gas insulated switchgears (GIS). Gas insulated transmission lines (GIL) are well-proven technologies operating under a voltage of at least 800 kV AC, their development for high voltage direct current (HVDC) applications is extremely challenging. Underground HVDC GIL technology is well-suited to carry very high power of several gigawatts (5 GW) per bipolar system over long distances with very low losses. This applies when overhead lines are not permitted due to their visual impact and public opposition, and when for the same allowable installation space, XLPE extruded HVDC cables cannot be used due to their limited power transmission capacity to about
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