Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductors and capacitors may result in periodic reversals of the direction of energy flow. The portion of power that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as active power (sometimes also called real power). The portion of power due to stored energy, which returns to the source in each cycle, is known as reactive power.
Electrical systems useful in everyday life
Increasingly, repair of electrical installations applies to problems with the installation, which allows the automatic opening and closing of the gate, for example, when entering the garage and so on. Such solutions are becoming more common due to its convenience and therefore need to repair this type of installation is becoming more common. First of all, the problem can occur in drives to the gates, which may not respond to user requests or for example open instead of closed. Systems control the opening and closing of gates and barriers are most commonly used in their construction, electrical components, so repair them must deal with the electrician.
History of electric power
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 the hopes of improving them for use in a commercial power system. One of Westinghouse's engineers, William Stanley, recognised the problem with connecting transformers in series as opposed to parallel and also realised that making the iron core of a transformer a fully enclosed loop would improve the voltage regulation of the secondary winding. Using this knowledge he built the first practical transformer based alternating current power system at Great Barrington, Massachusetts in 1886.6 Westinghouse would begin installing multi-voltage AC transformer systems in competition with the Edison company later that year. In 1888 Westinghouse would also licensed Nikola Tesla's US patents for a polyphase AC induction motor and transformer designs and hired Tesla for one year to be a consultant at the Westinghouse Electric & Manufacturing Company's Pittsburgh labs.
By 1888 the electric power industry was flourishing, and power companies had built thousands of power systems (both direct and alternating current) in the United States and Europe. These networks were effectively dedicated to providing electric lighting. During this time the rivalry between Thomas Edison and George Westinghouse's companies had grown into propaganda campaign over which form of transmission (direct or alternating current) was superior, a searies of events known as the "War of Currents". In 1891, Westinghouse installed the first major power system that was designed to drive a 100 horsepower (75 kW) synchronous electric motor, not just provide electric lighting, at Telluride, Colorado. On the other side of the Atlantic, Mikhail Dolivo-Dobrovolsky built a 20 kV 176 km three-phase transmission line from Lauffen am Neckar to Frankfurt am Main for the Electrical Engineering Exhibition in Frankfurt. In the US the AC/DC competition came to the end when Edison General Electric was taken over by their chief AC rival, the Thomson-Houston Electric Company, forming General Electric. In 1895, after a protracted decision-making process, alternating current was chosen as the transmission standard with Westinghouse building the Adams No. 1 generating station at Niagara Falls and General Electric building the three-phase alternating current power system to supply Buffalo at 11 kV.
Developments in power systems continued beyond the nineteenth century. In 1936 the first experimental HVDC (high voltage direct current) line using mercury arc valves was built between Schenectady and Mechanicville, New York. HVDC had previously been achieved by series-connected direct current generators and motors (the Thury system) although this suffered from serious reliability issues. In 1957 Siemens demonstrated the first solid-state rectifier, but it was not until the early 1970s that solid-state devices became the standard in HVDC. In recent times, many important developments have come from extending innovations in the ICT field to the power engineering field. 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 remote control of a power system's switchgear and generators.