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Lightning Arrester
A lightning arrester (alternative spelling lightning arrestor) (also called lightning isolator) is a device, essentially an air gap between an electric wire and ground, used on electric power transmission and telecommunication systems to protect the insulation and conductors of the system from the damaging effects of lightning. The typical lightning arrester has a high-voltage terminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from the surge is diverted through the arrester, in most cases to earth. In telegraphy and telephony, a lightning arrester is placed where wires enter a structure, preventing damage to electronic instruments within and ensuring the safety of individuals near them. Smaller versions of lightning arresters, also called surge arresters, are devices that are connected between each conductor in power and communications systems and the earth. These prevent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inductor
An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a coil. When the current flowing through the coil changes, the time-varying magnetic field induces an electromotive force (''emf'') (voltage) in the conductor, described by Faraday's law of induction. According to Lenz's law, the induced voltage has a polarity (direction) which opposes the change in current that created it. As a result, inductors oppose any changes in current through them. An inductor is characterized by its inductance, which is the ratio of the voltage to the rate of change of current. In the International System of Units (SI), the unit of inductance is the henry (H) named for 19th century American scientist Joseph Henry. In the measurement of magnetic circuits, it is equivalent to . Inductors have values that typically ra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semiconductor
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. Its conducting properties may be altered in useful ways by introducing impurities (" doping") into the crystal structure. When two differently doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers, which include electrons, ions, and electron holes, at these junctions is the basis of diodes, transistors, and most modern electronics. Some examples of semiconductors are silicon, germanium, gallium arsenide, and elements near the so-called "metalloid staircase" on the periodic table. After silicon, gallium arsenide is the second-most common semiconductor and is used in laser diodes, solar cells, microwave-frequency integrated circuits, and others. Silicon is a critical element ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spark Gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductors exceeds the breakdown voltage of the gas within the gap, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the "holding current". This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas. Usually, the action of ionizing the gas is violent and disruptive, often leading to sound (ranging from a ''snap'' for a spark plug to thunder for a lightning discharge), light and heat. Spark gaps were used historically in early electrical equipment, such as spark gap radio transmitters, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron's mass is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum ( spin) of a half-integer value, expressed in units of the reduced Planck constant, . Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: They can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Brog ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Television Antenna
A television antenna (TV aerial) is an antenna specifically designed for use with a television receiver (TV) to receive over-the-air broadcast television signals from a television station. Television reception is dependent upon the antenna as well as the transmitter. Terrestrial television is broadcast on frequencies from about 47 to 250 MHz in the very high frequency (VHF) band, and 470 to 960 MHz in the ultra high frequency (UHF) band in different countries. Television antennas are manufactured in two different types: "indoor" antennas, to be located on top of or next to the television set, and "outdoor" antennas, mounted on a mast on top of the owner's house.Johnson 1993 Antenna Engineering Handbook, 3rd Ed.', p. 29.5-29.6 They can also be mounted in a loft or attic, where the dry conditions and increased elevation are advantageous for reception and antenna longevity. Outdoor antennas are more expensive and difficult to install, but are necessary for adequate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lightning Strike
A lightning strike or lightning bolt is an electric discharge between the atmosphere and the ground. Most originate in a cumulonimbus cloud and terminate on the ground, called cloud-to-ground (CG) lightning. A less common type of strike, ground-to-cloud (GC) lightning, is upward-propagating lightning initiated from a tall grounded object and reaching into the clouds. About 25% of all lightning events worldwide are strikes between the atmosphere and earth-bound objects. Most are intracloud (IC) lightning and cloud-to-cloud (CC), where discharges only occur high in the atmosphere. Lightning strikes the average commercial aircraft at least once a year, but modern engineering and design means this is rarely a problem. The movement of aircraft through clouds can even cause lightning strikes. A single lightning event is a "flash", which is a complex, multistage process, some parts of which are not fully understood. Most CG flashes only "strike" one physical location, referred to as a " ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bushing (electrical)
In electric power, a bushing is a hollow electrical insulator that allows an electrical conductor to pass safely through a conducting barrier such as the case of a transformer or circuit breaker without making electrical contact with it. Bushings are typically made from porcelain, though other insulating materials are also used. Explanation All materials carrying an electric charge generate an electric field. When an energized conductor is near a material at earth potential, it can form very high field strengths, especially where the field lines are forced to curve sharply around the earthed material. The bushing controls the shape and strength of the field and reduces the electrical stresses in the insulating material. Bushing condenser A bushing must be designed to withstand the electrical field strength produced in the insulation, when any earthed material is present. As the strength of the electrical field increases, leakage paths may develop within the insulation. If th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ballistics
Ballistics is the field of mechanics concerned with the launching, flight behaviour and impact effects of projectiles, especially ranged weapon munitions such as bullets, unguided bombs, rockets or the like; the science or art of designing and accelerating projectiles so as to achieve a desired performance. A ballistic body is a free-moving body with momentum which can be subject to forces such as the forces exerted by pressurized gases from a gun barrel or a propelling nozzle, normal force by rifling, and gravity and air drag during flight. A ballistic missile is a missile that is guided only during the relatively brief initial phase of powered flight and the trajectory is subsequently governed by the laws of classical mechanics; in contrast to (for example) a cruise missile which is aerodynamically guided in powered flight like a fixed-wing aircraft. History and prehistory The earliest known ballistic projectiles were stones and spears, and the throwing stick. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High-voltage Transformer Fire Barriers
High-voltage transformer fire barriers, or transformer firewalls, transformer ballistic firewalls, transformer blast walls, are outdoor countermeasures against cascading failures in a national electric grid. The purpose of these barriers, like common fire barriers in building construction, is compartmentalisation of transformer fires, and compartmentalisation of transformer and bushing explosions―in which the fuel source of both fires and explosions is the transformer oil. Without compartmentalisation, one ruptured transformer could start its neighbouring transformer on fire and thus create a domino effect that would affect the surrounding electric grid, particularly during peak times. High-voltage transformer fire barriers are typically located in electrical substations, but may also be attached to buildings, such as valve halls or manufacturing plants with large electrical distribution systems, such as pulp and paper mills. Outdoor transformer fire barriers that are attac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force (EMF) across any other coils wound around the same core. Electrical energy can be transferred between separate coils without a metallic (conductive) connection between the two circuits. Faraday's law of induction, discovered in 1831, describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil. Transformers are used to change AC voltage levels, such transformers being termed step-up or step-down type to increase or decrease voltage level, respectively. Transformers can also be used to provide galvanic isolation between circuits as well as to couple stages of signal-processing circuits. Since the invention of the first constant-potential trans ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
