However, if direct current is used, the cable capacitance is charged solely when the cable is first energized or if the voltage level changes; there isn't a extra current required. In different words, transmitting electric AC power over lengthy distances inevitably results in a phase shift between voltage and present. Though HVDC conversion gear at the terminal stations is expensive, the total DC transmission-line costs over long distances are decrease than for an AC line of the identical distance.

Multilevel converters have the advantage that they permit harmonic filtering equipment to be lowered or eliminated altogether. CCC has remained only a distinct segment utility because of the advent of voltage-source converters (VSCs) which extra immediately handle turn-off points. The event of upper rated insulated-gate bipolar transistors (IGBTs), gate turn-off thyristors (GTOs), and integrated gate-commutated thyristors (IGCTs), has made HVDC systems more economical and dependable.

In India, vapeconsider   the multi-terminal North-East Agra challenge is planned for vaporwhite (click the next webpage) commissioning in 2015-2017. It's rated 6,000 MW, and vaporwhite it transmits energy on a ±800 kV bipolar line from two converter stations, at Biswanath Chariali and Alipurduar, vapingthink within the east to a converter at Agra, a distance of 1,728 km (1,074 mi). Even increased powers will be achieved by connecting two or more twelve-pulse converters in collection in each pole, as is used within the ±800 kV Xiangjiaba-Shanghai undertaking in China, which makes use of two twelve-pulse converter bridges in each pole, vaperesult every rated at four hundred kV DC and 1,600 MW.

The required converter stations are costly and have limited overload capacity. All electronic power converters generate some degree of harmonic distortion on the AC and DC methods to which they are linked, and vapetoward   HVDC converters aren't any exception. It is extremely expensive to supply harmonic filters capable of suppressing such harmonics, so a variant recognized because the twelve-pulse bridge, consisting of two six-pulse bridges in series with a 30° phase shift between them, is practically always used.

By way of comparability, AC harmonic filters of typical line-commutated converter stations cover almost half of the converter station space. Nevertheless, converter types corresponding to the two-degree converter, used with pulse-width modulation (PWM), still require some filtering, albeit lower than on line-commutated converter programs. The basic LCC configuration uses a three-section bridge rectifier known as a six-pulse bridge, containing six digital switches, every connecting one of the three phases to one in every of the two DC rails.

Early LCC methods used mercury-arc valves, which were rugged but required excessive maintenance. Like mercury arc valves, thyristors require connection to an exterior AC circuit in HVDC purposes to show them on and off.