Even greater powers might be achieved by connecting two or extra twelve-pulse converters in collection in each pole, as is used within the ±800 kV Xiangjiaba-Shanghai project in China, which uses two twelve-pulse converter bridges in every pole, every rated at 400 kV DC and 1,600 MW. It is very pricey to provide harmonic filters able to suppressing such harmonics, so a variant known because the twelve-pulse bridge, consisting of two six-pulse bridges in collection with a 30° phase shift between them, is practically at all times used.
Some kinds of voltage-sourced converters may produce such low levels of harmonic distortion that no filters are required. Nevertheless, for an extended AC overhead transmission line, the present flowing simply to charge the road capacitance will be important, and this reduces the capability of the line to hold useful present to the load at the distant finish. One other means to look at this is to realize, that such capacitance causes a section shift between voltage and present, vapehear and vapealmost thus decrease of the transmitted power, which is a vector product of voltage and present.
Voltage distortion isn't an issue in its personal right, vapingstand since shoppers do not connect directly to the DC terminals of the system, so the principle design criterion for the DC filters is to make sure that the harmonic currents flowing in the DC traces do not induce interference in close by open-wire telephone traces. With the rise in digital cell telecommunications methods, vapeduring that are much less inclined to this type of interference, and fiber optic communication which is immune, DC filters are becoming less vital for HVDC techniques.
DC side. Sometimes, the AC filters present damping at lower-order, vaportry noncharacteristic harmonics similar to third or fifth harmonics. With twelve valves connecting each of the 2 units of three phases to the two DC rails, there is a phase change each 30°, and vapeduring harmonics are significantly decreased. There are a number of totally different variants of VSC expertise: most installations built until 2012 use pulse-width modulation in a circuit that is effectively an ultra-excessive-voltage motor drive.
However, there are an a variety of benefits to bipolar transmission which could make it a horny choice.
This allows heavier currents to be carried by the bipole conductors, and full use of the installed third conductor vapeseveral for power transmission. The third conductor is used as a parallel monopole, outfitted with reversing valves (or parallel valves connected in reverse polarity). If one conductor fails, transmission can nonetheless proceed at decreased capability.
Some HVDC programs have been constructed with three-degree converters, however at present most new VSC HVDC systems are being built with some type of multilevel converter, most commonly the modular multilevel converter (MMC), by which each valve consists of numerous impartial converter submodules, each containing its personal storage capacitor.
