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| World’s first ±1,100 kV HVDC transformer. Image courtesy Siemens AG |
For
high voltage DC (Direct Current) transmission over 3000 km. The
transformer has a rating of 587 MVA. AC (Alternating Current) is
normally used for transmission because of the ease by which it can be
converted to different voltages using transformers. Transmission at very
high voltages of 400 kV (e.g. the line at Silliot Hill, which runs from
Moneypoint power station to Dunstown 400 kV sub-station) and over is
used because electric current is reduced proportionately as voltage is
increased. All electrical conductors have resistance and by reducing the
current, transmission losses are reduced. However AC is not without its
disadvantages and losses occur with AC through the capacitance between
lines and the ground. There are also inductive losses. For transmission
lines > 600 km, e.g. the interconnectors connecting Ireland to
Britain, DC is used to reduce losses.
https://press.siemens.com/.../worlds-first-1100-kv-hvdc...
A more detailed explanation of why such high voltages are used for transmission here:
A more detailed explanation of why such high voltages are used for transmission here: