low cost. It is principally used for rural electrification, but also finds use for larger isolated loads such as water pumps. Single-wire earth return is also used for HVDC over submarine power cables. Wireless power transmission Both Nikola Tesla and Hidetsugu Yagi attempted to devise systems for large scale wireless power transmission in the late 1800s and early 1900s, without commercial success. In November 2009, LaserMotive won the NASA 2009 Power Beaming Challenge by powering a cable climber 1 km vertically using a ground-based laser transmitter. The system produced up to 1 kW of power at the receiver end. In August 2010, NASA contracted with private companies to pursue the design of laser power beaming systems to power low earth orbit satellites and to launch rockets using laser power beams. Wireless power transmission has been studied for transmission of power from solar power satellites to the earth. A high power array of microwave or laser transmitters would beam power to a rectenna. Major engineering and economic challenges face any solar power satellite project. Security The Federal government of the United States stated that the power grid is susceptible to cyber-warfare. The United States Department of Homeland Security works with industry to identify vulnerabilities and to help industry enhance the security of control system networks. In June 2019, Russia conceded that it was "possible" its electrical grid is under cyber-attack by the United States. The New York Times reported that American hackers from the United States Cyber Command planted malware potentially capable of disrupting the Russian electrical grid. Records Highest capacity system: 12 GW Zhundong–Wannan（准东-皖南）±1100 kV HVDC. Highest transmission voltage (AC): planned: 1.20 MV (Ultra-High Voltage) on Wardha-Aurangabad line (India) – under construction. Initially will operate at 400 kV. worldwide: 1.15 MV (Ultra-High Voltage) on Ekibastuz-Kokshetau line (Kazakhstan) Largest double-circuit transmission, Kita-Iwaki Powerline (Japan). Highest towers: Yangtze River Crossing (China) (height: ) Longest power line: Inga-Shaba (Democratic Republic of Congo) (length: ) Longest span of power line: at Ameralik Span (Greenland, Denmark) Longest submarine cables: North Sea Link, (Norway/United Kingdom) – (length of submarine cable: ) NorNed, North Sea (Norway/Netherlands) – (length of submarine cable: ) Basslink, Bass Strait, (Australia) – (length of submarine cable: , total length: ) Baltic Cable, Baltic Sea (Germany/Sweden) – (length of submarine cable: , HVDC length: , total length: ) Longest underground cables: Murraylink, Riverland/Sunraysia (Australia) – (length of underground cable: ) See also Dynamic