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 Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

systems to protect the insulation and conductors of the system from the damaging effects of

lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an avera ...

. The typical lightning arrester has a

high-voltage High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and Electrical conductor, conductors that carry high ...

terminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the

power line An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-p ...

to the arrester, the

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

from the surge is diverted through the arrester, in most cases to earth. In

telegraphy Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas ...

and

telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...

, 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 the flow of the normal power or signal currents to ground, but provide a path over which high-voltage lightning current flows, bypassing the connected equipment. Their purpose is to limit the rise in voltage when a communications or power line is struck by lightning or is near to a lightning strike. If protection fails or is absent, lightning that strikes the electrical system introduces thousands of kilovolts that may damage the transmission lines, and can also cause severe damage to

transformers ''Transformers'' is a media franchise produced by American toy company Hasbro and Japanese toy company Tomy, Takara Tomy. It primarily follows the Autobots and the Decepticons, two alien robot factions at war that can transform into other forms ...

and other electrical or electronic devices. Lightning-produced extreme voltage spikes in incoming power lines can damage electrical home appliances or even cause death. Lightning arresters are used to protect

electric fence An electric fence is a barrier that uses electric shocks to deter people or animals from crossing a boundary. The voltage of the shock may have effects ranging from discomfort to death. Most electric fences are used for agricultural fencing a ...

s. They consist of a spark gap and sometimes a series

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 c ...

. Such type of equipment is also used for protecting transmitters feeding a

mast radiator Mast, MAST or MASt may refer to: Engineering * Mast (sailing), a vertical spar on a sailing ship * Flagmast, a pole for flying a flag * Guyed mast, a structure supported by guy-wires * Mooring mast, a structure for docking an airship * Radio ma ...

. For such devices the series inductance has usually just one winding. Fuss Sendemast Hirschlanden 28092011 1

Lightning arresters can form part of large electrical

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 and can fragment during transformer ruptures.

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 co ...

are required to defeat ballistics from small arms as well as projectiles from transformer bushings and lightning arresters, per '
NFPA 850
''.

Components

A potential target for a

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- ...

, such as an outdoor

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 ...

, is attached to the terminal labeled A in the photograph. Terminal E is attached to a long rod buried in the ground. Ordinarily no current will flow between the antenna and the ground because there is extremely high resistance between B and C, and also between C and D. The voltage of a lightning strike, however, is many times higher than that needed to move

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 ...

s through the two air gaps. The result is that electrons go through the lightning arresters rather than traveling on to the television set and destroying it. A lightning arrester may be a

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 conduct ...

or may have a block of a

semiconducting A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

material such as

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal s ...

zinc oxide Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement ...

. "Thyrite" was the trade name used by General Electric for the silicon carbide composite used in their arrester and varistor products. Some spark gaps are open to the air, but most modern varieties are filled with a precision gas mixture, and have a small amount of radioactive material to encourage the gas to

ionize Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...

when the voltage across the gap reaches a specified level. Other designs of lightning arresters use a glow-discharge tube (essentially like a neon glow lamp) connected between the protected conductor and ground, or voltage-activated solid-state switches called

varistor A varistor is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non- ohmic current–voltage characteristic that is similar to that ...

s or MOVs. Lightning arresters used in power substations are large devices, consisting of a porcelain tube several feet long and several inches in diameter, typically filled with discs of zinc oxide. A safety port on the side of the device vents the occasional internal explosion without shattering the porcelain cylinder. Lightning arresters are rated by the peak current they can withstand, the amount of energy they can absorb, and the breakover voltage that they require to begin conduction. They are applied as part of a lightning protection system, in combination with air terminals and bonding.

References

External links

Electrical Devices and How They Work, Part 14: Lightning Arresters
(article about lightning arresters and how they were used in early AC and DC power distribution systems), '' Popular Science'' monthly, February 1919, 5 unnumbered pages, scanned by

Google Books Google Books (previously known as Google Book Search, Google Print, and by its code-name Project Ocean) is a service from Google Inc. that searches the full text of books and magazines that Google has scanned, converted to text using optical ...

OSHA Electric Power eTool: Illustrated Glossary: Lightning ArrestersAn extensive dictionary of terms used with arresters at ArresterWorks.com History of arresters at ArresterWorks.com Graphic Overview of how an arrester worksNEMA Surge Protection Institute
{{Authority control Lightning Electrical safety

Components

See also

References

External links