Prof. dr. Aldo Canova

High voltage direct current (HVDC) consists of two converters working as a rectifier and inverter which are connected, through transformers and high voltage equipment, to two high voltage AC (HVAC) power networks. Such electrical infrastructures are spreading thanks to the advantages they offer and the possibility of overcoming the limits of the most widespread HVAC technology.

The first operational HVDC system dates back to 1954, created between the island of Gotland in the Baltic Sea and the mainland (Sweden), with a power of 20 MW. Which has over time been replaced with a 260 MW bipole transmission system. Other plants, all using mercury vapor valves, followed over the years, including: in 1965, the connection of Sardinia with the continent; in 1970, the Pacific DC Intertie, connecting the Pacific Northwest region and Los Angeles, United States; in 1973, the Nelson River Bipole in Canada.

Only since the 1970s, with the development of high voltage semiconductor converters, HVDC transmission systems, which had already proven indispensable for crossing long stretches of sea or for connecting electrical systems with different frequencies, began to show competitiveness also for the transmission of great powers over very long distances.

HVDC allows the long-distance transmission of large quantities of energy and installation costs are compensated by lower losses (breakeven point around 600-800 km). They are very useful in case of marine connections: being able to cross long stretches of sea, unlike HVAC which has limitations dictated by the need to compensate for the capacity of AC cables.

Moreover, HVDC allows the interconnection between big consumption centers and geographical areas in which we have large availability of renewable sources (see for example the three DC corridors, made up of underground cable of ± 525 kV, which in Germany are being laid for transfer sustainable energy from the north of the country to the south).

Finally, by crossing two converters directly facing each other (BackToBack) it allows the connection of alternating current networks that are not synchronous with each other (e.g. the first at 50 Hz and the second at 60 Hz).

Among the main advantages, environmental impact aspects must also be considered, including those relating to electric and magnetic fields.

After an introduction related to HVCD technology, the seminar will highlight the innovative aspects that need to be considered in simulations and measurements in electric and magnetic fields, considering that there are new aspects such as high static currents and voltages which are not present in traditional HVAC infrastructures. In particular, a couple of topics of interest are represented by the measurement of the static electric field due to the high voltage connection between the valve room and the power cables and the measurement of the disturbances generated by the harmonics along the DC lines.

Keywords: HVAC, HVDC, Magnetic and Electric Fields