Things come full ‘circuit’ for direct current!
CONVENTIONAL LOGIC says that alternating current (AC) is more suitable for transmission over long distances than direct current (DC) is. We were taught so when we studied Physics in school. We were told the same thing when we studied electrical engineering in college. Once there even raged a huge debate on which one was better, with great inventor Thomas Alva Edison pushing for DC, and his associate-turned-rival Nikola Tesla backing AC. Eventually, the AC system won. However, things seem to be coming a full circle (circuit?) for DC now – its usage is increasing with the advent of semi-conductors and electronics, the need to use renewable energy, the extensive use of power back-ups, and the fact that DC can now be transmitted over long distances (thanks to power electronics). Experts feel that it may take several decades, but the use of DC will increase as compared to AC. Demand is being driven by the need to conserve energy and obtain energy from renewable sources. Since renewable energy is essentially DC power, it has to be converted into AC first, which causes energy loss. Similarly, semi-conductors, used extensively in household appliances, use DC. In homes, AC is converted into DC, which again causes energy to be wasted. Power back-up devices, so common nowadays, essentially converted DC into AC, again an inefficient way of using electricity. Power electronics, or semi-conductor switching devices, have made it possible to transmit DC at high voltage over long distances, longer even than is possible for AC. These are called high voltage direct current, or HVDC, systems. (An HVDC line exists in Maharashtra, India, between Chandrapur, and Padghe near Mumbai.) Sara Ledwith of Reuters news agency has written an excellent piece on the topic, which you can read here.
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