High-voltage direct present (HVDC) expertise affords a number of benefits in comparison with alternating present transmission techniques. For instance, it permits extra environment friendly bulk energy switch over lengthy distances. However, value is a vital variable within the equation. Once put in, HVDC transmission techniques are an integral a part of energy system, bettering stability, reliability, and transmission capability.
Typical utility-scale energy crops generate alternating present (AC) electrical energy, and masses run on AC energy. Thus, the vast majority of transmission traces carrying energy around the globe are of the AC kind. However, there are cases when high-voltage direct present (HVDC) transmission techniques provide vital advantages.
“One large benefit to HVDC is the effectivity of energy transmission over lengthy distances,” George Culbertson, vice chairman of energy supply markets for HDR, informed POWER. “If the transmission line route is longer than about 300 miles, DC is a greater possibility as a result of AC traces have extra line losses than DC for bulk energy switch.”
Converting from AC to DC
The problem, nevertheless, is that to transmit through HVDC, two converter stations are wanted. First, the AC energy have to be transformed to DC to start the transmission course of, after which when it will get to the specified tie-in vacation spot, the DC energy have to be transformed again to AC to be utilized on the grid.
Conversion expertise is well-established. Electrical pioneers had been engaged on the constructing blocks for HVDC-links again within the late 1800s. Conventional HVDC converter expertise is predicated on the usage of line-commutated or phase-commutated converters. In 1954, ASEA, the predecessor of ABB, used this basic expertise using mercury arc valves to assemble the world’s first industrial HVDC hyperlink between Västervik, on the east coast of Sweden, and Ygne, on the island of Gotland within the Baltic Sea. The authentic Gotland hyperlink may switch 20 MW over a 98-kilometer (km)-long submarine cable with a voltage of 100 kV. The service was re-engineered in 1970, growing capability to 30 MW at a voltage of 150 kV by means of the addition of a thyristor valve bridge.
ASEA continued to push boundaries, growing new HVDC techniques in the course of the many years that adopted. In 1997, ABB commissioned the world’s first HVDC demonstration challenge utilizing voltage supply converters (VSCs). VSC expertise makes use of gate turn-off switching units, comparable to insulated-gate bipolar transistors (IGBTs), to carry out the conversion. An IGBTs excessive switching frequency functionality permits more-precise VSC management and less-complex circuit configuration by means of the usage of pulse width modulation methods. ABB named its new VSC-based product HVDC Light.
VSC expertise was additional improved when Siemens launched a modular multilevel converter (MMC). The Trans Bay Cable challenge, which runs between San Francisco and Pittsburg, California, was accomplished in 2010, utilizing Siemens’ HVDC Plus system. MMC expertise affords wonderful harmonic efficiency and diminished energy losses in comparison with earlier VSCs. All HVDC producers are making use of MMC expertise in VSCs as we speak.
Platform to Shore
Vince Curci, underground transmission challenge supervisor with HDR, mentioned one of many benefits of VSC expertise is that it is extremely compact. “They require perhaps 30% of the realm of a standard converter and about 50% of the burden,” Curci mentioned. That makes them a good selection for offshore wind farms. “A 600-MW VSC requires lower than one acre of land, whereas a standard converter requires three or 4 acres. So, the benefit of this new expertise is you could put them at sea on a small footprint and switch energy to land through submarine cables.”
One instance of that’s the DolWin2 challenge (Figure 1). TenneT, a European transmission system operator with operations within the Netherlands and Germany, required a…