However, if direct current is used, the cable capacitance is charged solely when the cable is first energized or vaperesult if the voltage degree changes; there isn't any extra present required. In different phrases, transmitting electric AC energy over lengthy distances inevitably leads to a part shift between voltage and current. The thyristor plus its grading circuits and other auxiliary gear is named a thyristor level. Multilevel converters have the benefit that they permit harmonic filtering tools to be lowered or eradicated altogether.

Since one terminal of the converters is connected to earth, vaperesult the return conductor need not be insulated for the complete transmission voltage which makes it much less expensive than the high-voltage conductor. The development of higher rated insulated-gate bipolar transistors (IGBTs), gate turn-off thyristors (GTOs), and integrated gate-commutated thyristors (IGCTs), has made HVDC methods extra economical and reliable. When a fault develops in a line, vapewithout with earth return electrodes installed at each finish of the road, approximately half the rated power can continue to circulation utilizing the earth as a return path, working in monopolar mode.

Even greater powers might be achieved by connecting two or vapepresident extra twelve-pulse converters in collection in each pole, as is used within the ±800 kV Xiangjiaba-Shanghai project in China, which makes use of two twelve-pulse converter bridges in every pole, each rated at 400 kV DC and vapingper 1,600 MW.

Pulse-width modulation (PWM) is often used to improve the harmonic distortion of the converter. Because of this, harmonic filters are practically at all times required at the AC terminals of such converters, vaperesult and in HVDC transmission schemes using overhead strains, might also be required on the DC side.

DC filters are required only for HVDC transmission methods involving overhead lines. Converter transformers for vapingsense LCC HVDC schemes are quite specialised because of the excessive ranges of harmonic currents that movement through them, and since the secondary winding insulation experiences a everlasting DC voltage, which impacts the design of the insulating construction inside the tank.