The risks of HVDC are conversion, switching, manipulation, availability, and maintenance. HVDC is much less dependable and has decreased availability than alternating contemporary (AC) structures, specifically because of the more conversion gadget. Single-pole structures have availability of approximately 98.5%, with approximately a 3rd of the downtime unscheduled because of faults. Fault-tolerant bipole structures offer excessive availability for 50% of the hyperlink potential, however, the availability of the overall potential is set at 97% to 98%. The required converter stations are high-priced and feature confined overload potential. At smaller transmission distances, the losses withinside the converter stations can be larger than in an AC transmission line for an identical distance. The Frontier Utilities Rates price of the converters won’t be offset with the aid of using discounts in line production price and decrease line loss. Operating an HVDC scheme calls for many spare components to be kept, regularly solely for one gadget, as HVDC structures are much less standardized than AC structures, and era adjustments greater quickly.
In the assessment of AC structures, figuring out multi-terminal structures is complex (mainly with line commutated converters), as is increasing present schemes to multi-terminal structures. Controlling energy waft in a multi-terminal DC gadget calls for precise communique among all of the terminals; energy waft ought to be actively regulated with the aid of using the converter manipulate gadget rather than counting on the inherent impedance and segment attitude residences of an AC transmission line. Multi-terminal structures are rare. As of 2012, the handiest are in service: the Hydro Québec – New England transmission among Radisson, Sandy Pond, and Nicolet and the Sardinia–mainland Italy hyperlink which become changed in 1989 to additionally offer energy to the island of Corsica.
High-voltage DC circuit breaker
HVDC circuit breakers are tough to construct due to arcing: below AC the voltage inverts, and in doing so crosses 0 volts, dozens of instances a second. An AC arc will “self-extinguish” at such 0-crossing factors due to the fact there can not be an arc in which there’s no ability difference. DC will by no means pass 0 volts and by no means self-extinguish, so arc distance and period are ways extra with DC than with the identical voltage AC. In this method a few mechanisms ought to be blanketed withinside the circuit breaker to pressure contemporary to 0 and extinguish the arc, in any other case arcing and call put on might be too remarkable to permit dependable switching. In November 2012, ABB introduced the improvement of the world’s first ultrafast HVDC circuit breaker. Mechanical circuit breakers are too gradual to be used in HVDC grids, even though they were used for years in different applications. Conversely, semiconductor breakers are rapid and sufficient however have excessive resistance while conducting, losing electricity and producing warmness in everyday operation. The ABB breaker combines semiconductor and mechanical breakers to provide a “hybrid breaker” with each a quick wreck time and a low resistance in everyday operation.
Costs
Generally, companies of HVDC structures, along with Alstom, Siemens, and ABB, now no longer specify the price info of specific projects. It can be taken into consideration an industrial dependence between the company and the client. Costs range extensively relying on the specifics of the project. A specified contrast of DC vs. AC transmission fees can be required in conditions in which there’s no clean technical gain to DC and inexpensive reasoning on my drives the selection. However, a few practitioners have supplied some information: For an eight GW forty km hyperlink laid below the English Channel, the subsequent are approximate number one gadget fees for a 2000 MW 500 kV bipolar traditional HVDC hyperlink.