Electric power system
The majority of these systems rely upon three-phase AC power—the standard for large-scale power transmission and distribution across the modern world.
[4] That same year in London, Lucien Gaulard and John Dixon Gibbs demonstrated the "secondary generator"—the first transformer suitable for use in a real power system.
In 1885, Ottó Titusz Bláthy working with Károly Zipernowsky and Miksa Déri perfected the secondary generator of Gaulard and Gibbs, providing it with a closed iron core and its present name: the "transformer".
[8] Also in 1885 George Westinghouse, an American entrepreneur, obtained the patent rights to the Gaulard-Gibbs transformer and imported a number of them along with a Siemens generator, and set his engineers to experimenting with them in hopes of improving them for use in a commercial power system.
[9] Using this knowledge he built a multi-voltage transformer-based alternating-current power system serving multiple homes and businesses at Great Barrington, Massachusetts in 1886.
[15] On the other side of the Atlantic, Mikhail Dolivo-Dobrovolsky and Charles Eugene Lancelot Brown, built the first long-distance (175 kilometers (109 miles)) high-voltage (15 kV, then a record) three-phase transmission line from Lauffen am Neckar to Frankfurt am Main for the Electrical Engineering Exhibition in Frankfurt, where power was used to light lamps and run a water pump.
1 generating station at Niagara Falls and General Electric building the three-phase alternating current power system to supply Buffalo at 11 kV.
In 1936 the first experimental high voltage direct current (HVDC) line using mercury arc valves was built between Schenectady and Mechanicville, New York.
[17] HVDC had previously been achieved by series-connected direct current generators and motors (the Thury system) although this suffered from serious reliability issues.
[20] In 1979, a European consortium including Siemens, Brown Boveri & Cie and AEG realized the record HVDC link from Cabora Bassa to Johannesburg, extending more than 1,420 kilometers (880 miles) that carried 1.9 GW at 533 kV.
For example, the development of computers meant load flow studies could be run more efficiently, allowing for much better planning of power systems.
Advances in information technology and telecommunication also allowed for effective remote control of a power system's switchgear and generators.
DC power remains the only practical choice in digital systems and can be more economical to transmit over long distances at very high voltages (see HVDC).
Alternating current power is typically supplied by a rotor that spins in a magnetic field in a device known as a turbo generator.
The appliances found in residential settings, for example, will typically be single-phase operating at 50 or 60 Hz with a voltage between 110 and 260 volts (depending on national standards).
These include voltage sags, dips and swells, transient overvoltages, flicker, high-frequency noise, phase imbalance and poor power factor.
[30] Choice of conductors is based on considerations such as cost, transmission losses and other desirable characteristics of the metal like tensile strength.
Despite their relatively simple function, their speed of operation (typically in the order of nanoseconds[36]) means they are capable of a wide range of tasks that would be difficult or impossible with conventional technology.
HVDC is used because it proves to be more economical than similar high voltage AC systems for very long distances (hundreds to thousands of kilometres).
Power electronics even appear in modern residential air conditioners allow are at the heart of the variable speed wind turbine.
And second, fuses are typically inadequate as the sole safety device in most power systems as they allow current flows well in excess of that that would prove lethal to a human or animal.
In higher powered applications, the protective relays that detect a fault and initiate a trip are separate from the circuit breaker.
Air is typically no longer sufficient to quench the arc that forms when the contacts are forced open so a variety of techniques are used.
One of the most popular techniques is to keep the chamber enclosing the contacts flooded with sulfur hexafluoride (SF6)—a non-toxic gas with sound arc-quenching properties.
[40] Residual current devices require a separate neutral line for each phase and to be able to trip within a time frame before harm occurs.
The active line would then be run through a main isolating switch in the fuse box and then split into one or more circuits to feed lighting and appliances inside the house.
If this casing were to become live, the theory is the connection to earth would cause an RCD or fuse to trip—thus preventing the future electrocution of an occupant handling the appliance.
Electrical designs for larger commercial systems are usually studied for load flow, short-circuit fault levels and voltage drop.
The objectives of the studies are to assure proper equipment and conductor sizing, and to coordinate protective devices so that minimal disruption is caused when a fault is cleared.
[43] In the United States, the National Electrical Code requires commercial systems to be built with at least one 20 A sign outlet in order to light outdoor signage.
