Environmental Engineering Reference
In-Depth Information
majority of electricity comes in the form of alternating current AC which
switches direction back and forth many times a second and which drives
almost all electric motors and appliances - in contrast to direct current
DC electricity which flows continuously in one direction. Alternating
current has been the preferred option for most dispatch of electricity
around the grid, because it is easier to adapt to different voltage levels. But
HVDC is better for transmitting large amounts of power over long dis-
tances with lower capital costs and lower transmission losses than HVAC.
Therefore HVDC power transmission may become more important
in a low-carbon economy that is increasingly electrified via renewable
power coming from distant parts (see Desertec project in Solar power
section in Chapter 6). Transmission loss can be nearly eliminated by using
superconductor cables, but this is costly. For example the cable is far more
complex to manufacture than copper wire, and the cable has to be cooled.
Since it will probably be impossible to ever reduce transmission losses to
zero, there is one clear advantage in micro-generation that is unlikely to
Stacks of thyristors - semiconductor devices capable of switching power on
a megawatt scale - hang from the ceiling of a “valve hall”. Thyristors lie at the
heart of high voltage direct current (HVDC) conversion, and the ones pictured
here are part of a joint project between Siemens and BHEL to supply power, via
HVDC cables, to the area around New Delhi in India.
