Challenges in high voltage and ultra high voltage AC and DC field testing

Abstract

One of the challenging issues with high voltage network connections, be it for off-shore windfarms, inter-network HVDC connections, or simply overhead line replacement is to test the complete connections before bringing them into service. Even if all components are individually tested before being brought onto the construction site the final assembly needs to tested as a complete system before it is put in service. There are currently several challenges in the area of testing 150KV and higher voltages: First for short length cables the cost of measurement is prohibitive due to the fact that most current testing equipment is designed for laboratory use, requires specialized and time consuming setup and is therefore uneconomical to use. Another challenging area is the testing of long cables completely assembled: Current testing technology requires multiple test systems to be interconnected, resulting in severe logistics and technical challenges and even then most time testing is done in sections. Furthermore for HVDC and voltages above 400kV testing is limited to laboratory tests mainly by lack of appropriate testing equipment and standards. A new technology development has promising capacities for these field testing needs: Differential Resonance Technology (DRT) is developed based on long years of experience in VLF field testing and before that specialised laboratory test equipment. Differential resonance technology, as the name describes uses the differential of 2 resonance circuits to create a high-voltage low frequency signal in the range from 0,1 Hz to 10Hz. In this way compact and powerful testing equipment for High and Ultra High voltage and DC can be constructed. Current status: the first prototype systems have been build, currently tested up to 200kV RMS, and the current product range goes from 100KV up to 400KV (RMS) and 600KV DC, and cable lengths over 100KM. Scientific work on raising the output voltage to 800KV RMS and higher load capacities for future use has been started. The paper will focus in detail on the design issues of Digital Resonance Technology High Voltage testing systems. In addition we will present typical test applications for long range cables for off-shore windmills parks and for high voltage cable projects. (3 pages)