Electricity + Control October 2017

Ensight Energy Solutions is an energy productivity specialist firm that works with industrial companies to transform their energy output profiles so that energy waste is minimised, systems are optimised and profit is maximised.

HighVoltage Direct Current (HVdc) With technological advancements, particularly with thyristor valve-controlled converters (converting between ac and dc), dc is experiencing an increas- ing demand in modern applications. At greater dis- tances (within the order of hundreds to thousands of kilometres), the power needed to move ac be- comes significant.This inefficiency can be mitigated by using HVdc, which requires less cabling than ac infrastructure and also less power to move current. However, the thyristor converter technology is capi- tal intensive, and thus HVdc only becomes econom- ically viable over great distances, whereby the lower capital costs required for dc cabling infrastructure and mitigations of power expenditure on moving current can compensate for cost of converters. Dc would be used in situations whereby the en- ergy source is thousands of kilometres away from the energy users, and transporting the fuel would not be financially sensible (in terms of operating transport costs and/or logistics infrastructure cap- ital requirements). Furthermore, dc transmission infrastructure can integrate renewable energy technologies, such as wind and solar power, which use dc. Also, HVdc undersea power cables are being used to transfer power between countries to share energy assets. Interestingly, dc technology can be used to compliment ac infrastructure, rather than compete with it. Two ac circuits of different frequencies cannot function as a uniform system. However, by using converters, one synchronised system could be achieved. Conclusion It is clear that ac and dc each have their strengths and weaknesses. The ability of ac to have voltage stepped up or down allows for high voltages, there- by minimising the current level and mitigating pow- er loss in transmission. However, dc cannot induce a magnetic flux. A large amount of power is in fact used to move the ac across a cable, and this be- comes particularly high for situations wherein

the power lines are thousands of kilometres long. In this case, using a HVdc system may be feasible, as the high capital costs of thyristors could be out- weighed by the savings achieved by mitigating the cabling costs and the power expenditure of moving current across a circuit. With changing technologies, it is surmised that ac and dc do not have to compete in their tradition- al manner, wherein one current type was support- ed to render the other obsolete. Instead, various applications can be characterised as being suited to either ac or dc, after comparing the parameters of the application in conjunction with the strengths and weaknesses of each current type. Ac and dc can share the market for power distribution, and can even complement each other in terms of fre- quency synchronisation.Thus, a nuanced approach to power distribution would be important in achiev- ing optimal energy efficiency. Bibliography [1] Ardelean M., Minnebo P. 2015. HVDC Sub- marine Power Cables in the World. European Commission. [2] Clean Line Energy Partners. (n.d.). Retrieved from www.cleanlineenergy.com: www.clean- lineenergy.com/technology/hvdc [3] Damsky B. 2002. June 1. Primer on transmis- sion: Ac vs. dc. (E. L. Power, Interviewer). [4] DeDad J A. 1998. April 1. The Basics of Alter- nating Current. Retrieved from www.ecmweb. com: http://www.ecmweb.com/content/ba- sics-alternating-current [5] Department of Energy (US). 2014. November 18. The War of the Currents: Ac vs. dcPower. Retrieved from www.energy.gov: https://ener- gy.gov/articles/war-currents-ac-vs-dc-power [6] Electronics Tutorials. (n.d.). Ohms Law and Power. Retrieved from www.electronics-tuto- rials.ws: www.electronics-tutorials.ws/dccir- cuits/dcp_2.html [7] Eskom. 2014. May. Standard Condition of Sup- ply for Large Supplies. [8] Khan Academy. (n.d.). What is faraday’s law? Retrieved from www.khanacademy.org: https://www.khanacademy.org/science/phys- ics/magnetic-forces-and-magnetic-fields/mag- netic-flux-faradays-law/a/what-is-faradays-law [9] KuphaldtTR. (n.d.). Lessons in Electric Circuits. Design Science Licence. [10]The Economist. 2017. January 14. Transmitting power over thousands of kilometres requires a new electricity infrastructure. Rise of the su- pergrid.

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o is ikhil aido (QHUJ\ (IÀFLHQF\ ht Engineer at Ensig Energy Solutions.

nikhil.naidoo@ensight.solutions dillon.bensusan@ensight.solutions www.ensight.solutions

38 Electricity + Control

OCTOBER 2017