High Voltage Transmission
High voltage is used for electric power transmission to reduce the energy lost in the resistance of the wires. For a given quantity of power transmitted and size of conductor, doubling the voltage will deliver the same power at only half the current. Since the power lost as heat in the wires is proportional to the square of the current, but does not depend on the voltage, doubling the voltage reduces the line-loss loss per unit of electrical power delivered by a factor of 4. While power lost in transmission can also be reduced by increasing the conductor size, larger conductors are heavier and more expensive.
High voltages cannot easily be used for lighting and motors, and so transmission-level voltages must be reduced to values compatible with end-use equipment. Transformers are used to change the voltage level in alternating current (AC) transmission circuits. AC became dominant in the War of Currents competition between the direct current (DC) of Thomas Edison and the AC of Nikola Tesla and George Westinghouse because transformers made voltage changes practical and generators using AC were more efficient than those using DC.
Practical conversion between AC and high power high voltage DC became possible with the development of power electronics devices such as mercury arc valves and, starting in the 1970s, semiconductor devices such as thyristors and later variants such as integrated gate-commutated thyristors (IGCTs), MOS controlled thyristors (MCTs) and insulated-gate bipolar transistors (IGBT).
Read more about this topic: High-voltage Direct Current
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