Misplaced Pages

#756243

55-461: Ethiopian Electric Power owns and operates the Ethiopian national power grid with all high voltage power transmission lines above 66 kV including all attached electrical substations and almost all power plants within the national power grid (with the exception of some co-generation power plants belonging to the state-owned Ethiopian Sugar Corporation ). Ethiopian Electric power is almost

110-541: A 100-watt light bulb for approximately 2 months). However, an average bolt of positive lightning (from the top of a thunderstorm) may carry a current of 300 to 500 kiloamperes, transfer a charge of up to 300 coulombs, have a potential difference up to 1 gigavolt (a billion volts), and may dissipate 300 GJ of energy (72 tons TNT, or enough energy to light a 100-watt light bulb for up to 95 years). A negative lightning strike typically lasts for only tens of microseconds, but multiple strikes are common. A positive lightning stroke

165-497: A blast of high pressure air, a special dielectric gas (such as SF 6 under pressure), or immersion in mineral oil to quench the arc when the high voltage circuit is broken. Wiring in equipment such as X-ray machines and lasers requires care. The high voltage section is kept physically distant from the low voltage side to reduce the possibility of an arc forming between the two. To avoid coronal losses, conductors are kept as short as possible and free of sharp points. If insulated,

220-542: A certain threshold. Equipment and conductors that carry high voltage warrant special safety requirements and procedures . High voltage is used in electrical power distribution , in cathode-ray tubes , to generate X-rays and particle beams , to produce electrical arcs , for ignition, in photomultiplier tubes , and in high-power amplifier vacuum tubes , as well as other industrial, military and scientific applications. The numerical definition of high voltage depends on context. Two factors considered in classifying

275-584: A circuit includes a neutral or mid-point conductor identified by colour, the colour used shall be blue. In all installations the earth or protective conductor will remain green-and-yellow. RCDs were now required for most outlets in domestic premises or otherwise for general use by unskilled persons. Issued with red cover. Amended ( no. 1) and reprinted in 2011 (green cover), amended ( no. 2) Aug 2013, amended ( no. 3) and reprinted 2015 (yellow cover). Amendment 1 replaced Periodic inspection reports (PIRs) with Electrical Installation Condition Reports (EICRs),

330-413: A direct strike on persons or property. However, lightning can also create dangerous voltage gradients in the earth, as well as an electromagnetic pulse , and can charge extended metal objects such as telephone cables, fences, and pipelines to dangerous voltages that can be carried many miles from the site of the strike. Although many of these objects are not normally conductive, very high voltage can cause

385-417: A few small points of contact become the last to separate. The current becomes constricted to these small hot spots , causing them to become incandescent, so that they emit electrons (through thermionic emission ). Even a small 9 V battery can spark noticeably by this mechanism in a darkened room. The ionized air and metal vapour (from the contacts) form plasma , which temporarily bridges the widening gap. If

440-518: A hazard is presented to maintenance and operating personnel due to the possibility of a high-intensity electric arc . Maximum temperature of an arc can exceed 10,000 kelvins , and the radiant heat, expanding hot air, and explosive vaporization of metal and insulation material can cause severe injury to unprotected workers. Such switchgear line-ups and high-energy arc sources are commonly present in electric power utility substations and generating stations, industrial plants and large commercial buildings. In

495-421: A high-voltage transmission line or substation may result in high currents flowing along the surface of the earth, producing an earth potential rise that also presents a danger of electric shock. For high voltage and extra-high voltage transmission lines, specially trained personnel use " live line " techniques to allow hands-on contact with energized equipment. In this case the worker is electrically connected to

550-406: A human body will be relatively constant as long as contact is maintained, unlike with electrostatic machines which generally take longer to build up charges, and the voltage will be much higher than the break-down voltage of human skin. As a consequence, the output of a Tesla coil can be dangerous or even fatal. Depending on the prospective short-circuit current available at a switchgear line-up,

605-486: A leg. Electricity can flow between two conductors in high voltage equipment and the body can complete the circuit. To avoid that from happening, the worker should wear insulating clothing such as rubber gloves, use insulated tools, and avoid touching the equipment with more than one hand at a time. An electrical current can also flow between the equipment and the earth ground. To prevent that, the worker should stand on an insulated surface such as on rubber mats. Safety equipment

SECTION 10

#1732776221757

660-467: A person's body provides a path for current flow, causing tissue damage and heart failure. Other injuries can include burns from the arc generated by the accidental contact. These burns can be especially dangerous if the victim's airway is affected. Injuries may also be suffered as a result of the physical forces experienced by people who fall from a great height or are thrown a considerable distance. Low-energy exposure to high voltage may be harmless, such as

715-465: A relatively few electrons move. These devices have a limited amount of stored energy, so the average current produced is low and usually for a short time, with impulses peaking in the 1 A range for a nanosecond. The discharge may involve extremely high voltage over very short periods, but to produce heart fibrillation, an electric power supply must produce a significant current in the heart muscle continuing for many milliseconds , and must deposit

770-788: A section on surge protection devices (SPDs) was introduced, and some details relating to medical locations were added. Amendment 2 added a new section on electric vehicle charging. Amendment 3 introduced requirements for the use of non-combustable consumer units (or enclosures) in domestic premises, along with use of metal wiring/containment clips in certain situations, and expanded use of RCDs into commercial/industrial spaces. New sections have been added relating to microgeneration and solar photovoltaic systems , and breakers (including high resilience breaker layout). Issued with blue cover. Amended February 2020 ( no. 1), changing rules on car charging. Amended ( no. 2) and reprinted March 2022 (brown cover). Amended ( no. 3) July 2024, introducing

825-410: A supplement was issued 'on use in metric terms' in 1969, amended and reprinted 'in metric units' in 1970, reprinted in 1972 and 1973, amended and reprinted 1974 and 1976. The 2004 amendment saw major changes to wire colouring, following European-wide harmonisation efforts. Quoting the amendment document: Amendment No 2 : 2004 to BS 7671 : 2001 implements the cable core colours introduced in

880-617: A total energy in the range of at least millijoules or higher. Relatively high current at anything more than about fifty volts can therefore be medically significant and potentially fatal. During the discharge, these machines apply high voltage to the body for only a millionth of a second or less. So a low current is applied for a very short time, and the number of electrons involved is very small. Despite Tesla coils superficially appearing similar to Van de Graaff generators, they are not electrostatic machines and can produce significant radio frequency currents continuously. The current supplied to

935-485: A transmitting antenna is dangerous for this reason, and a high-frequency Tesla coil can sustain a spark with only one endpoint. Protective equipment on high-voltage transmission lines normally prevents formation of an unwanted arc, or ensures that it is quenched within tens of milliseconds. Electrical apparatus that interrupts high-voltage circuits is designed to safely direct the resulting arc so that it dissipates without damage. High voltage circuit breakers often use

990-934: A voltage as high voltage are the possibility of causing a spark in air, and the danger of electric shock by contact or proximity. The International Electrotechnical Commission and its national counterparts ( IET , IEEE , VDE , etc.) define high voltage as above 1000  V for alternating current , and at least 1500 V for direct current . In the United States, the American National Standards Institute (ANSI) establishes nominal voltage ratings for 60 Hz electric power systems over 100 V. Specifically, ANSI C84.1-2020 defines high voltage as 115 kV to 230 kV, extra-high voltage as 345 kV to 765 kV, and ultra-high voltage as 1,100 kV. British Standard BS 7671 :2008 defines high voltage as any voltage difference between conductors that

1045-572: Is BS 7671:2018+A3:2024 (18th Edition, amendment 3) issued in 2024. The regulations in BS7671 apply to the design, selection, erection and verification of electrical installations within: Exclusions: BS 7671 only covers electrical systems with the following characteristics: This includes low-voltage installations, as found in most domestic and commercial properties, and extra-low-voltage systems, but excludes high voltage , as found in generation, transmission and distribution networks. The standard

1100-481: Is U+26A1, the symbol "⚡︎" . The common static electric sparks seen under low-humidity conditions always involve voltage well above 700 V. For example, sparks to car doors in winter can involve voltages as high as 20,000 V. Electrostatic generators such as Van de Graaff generators and Wimshurst machines can produce voltages approaching one million volts at several amps, but typically don't last long enough to cause damage. Induction coils operate on

1155-530: Is classified as voltages in the range of 345,000– 765,000 V. In electronics systems, a power supply that provides greater than 275,000 volts is called an EHV Power Supply , and is often used in experiments in physics. The accelerating voltage for a television cathode ray tube may be described as extra-high voltage or extra-high tension (EHT), compared to other voltage supplies within the equipment. This type of supply ranges from 5 kV to about 30 kV. The Unicode text character representing "high voltage"

SECTION 20

#1732776221757

1210-538: Is done by the also state-owned sister company Ethiopian Electric Utility . Small and isolated self-contained power generation systems and power plants not attached to the national power grid do also exist in Ethiopia with generation capacities of up to 5MW e . These local power producers do not belong to Ethiopian Electric Power and can be privately owned or owned by regional authorities. The power transmission and power distribution from those self-contained power plants

1265-503: Is extinguished every time the current goes through a zero crossing , and must reignite during the next half-cycle to maintain the arc. Unlike an ohmic conductor, the resistance of an arc decreases as the current increases. This makes unintentional arcs in an electrical apparatus dangerous since even a small arc can grow large enough to damage equipment and start fires if sufficient current is available. Intentionally produced arcs, such as used in lighting or welding , require some element in

1320-675: Is higher than 1000 VAC or 1500 V ripple-free DC, or any voltage difference between a conductor and Earth that is higher than 600 VAC or 900 V ripple-free DC. Electricians may only be licensed for particular voltage classes in some jurisdictions. For example, an electrical license for a specialized sub-trade such as installation of HVAC systems, fire alarm systems, closed-circuit-television systems may be authorized to install systems energized up to only 30 volts between conductors, and may not be permitted to work on mains-voltage circuits. The general public may consider household mains circuits (100 to 250 VAC), which carry

1375-480: Is invisible but has a sweet odor. It oxidizes to nitrogen dioxide within a few minutes, which has a yellow or reddish-brown color depending on concentration and smells of chlorine gas like a swimming pool. Ozone is invisible but has a pungent smell like that of the air after a lightning storm. It is a short-lived species and half of it breaks down into O 2 within a day at normal temperatures and atmospheric pressure. Hazards due to lightning obviously include

1430-741: Is maintained by the Joint IET/BSI Technical Committee JPEL/64, the UK National Committee for Wiring Regulations, and published jointly by the IET (formerly IEE ) and BSI. Although the IET and BSI are non-governmental organisations and the Wiring Regulations are non-statutory, they are referenced in several UK statutory instruments , and in most cases, for practical purposes, have legal force as

1485-407: Is not a fixed minimum for producing spark breakdown, but it is a rule-of-thumb. For air at STP, the minimum sparkover voltage is around 327 volts, as noted by Friedrich Paschen . While lower voltages do not, in general, jump a gap that is present before the voltage is applied, interrupting an existing current flow with a gap often produces a low-voltage spark or arc . As the contacts are separated,

1540-668: Is not part of the business operations of Ethiopian Electric Power either. The company was formed in 1956 as the Ethiopian Electric Light & Power Authority (EELPA), which bundled all Ethiopian activities around electricity in a single organization. In 1996, EELPA was split into the Ethiopia Electric Authority (EEA), taking over all regulating activities and a company, Ethiopian Electric Power Corporation (EEPCo), bundling all activities from power generation to household delivery. In 2013, EEPCo

1595-691: Is now used in modified form in U.S. National Electrical Code and in the Canadian Electrical Code . Intrinsic safety apparatus is now approved for use in North American applications. Electrical discharges, including partial discharge and corona , can produce small quantities of toxic gases, which in a confined space can be a health hazard. These gases include oxidizers such as ozone and various oxides of nitrogen . They are readily identified by their characteristic odor or color, and thus contact time can be minimized. Nitric oxide

1650-649: Is tested regularly to ensure it is still protecting the user. Test regulations vary according to country. Testing companies can test at up 300,000 volts and offer services from glove testing to Elevated Working Platform (or EWP) testing. Contact with or close approach to line conductors presents a danger of electrocution . Contact with overhead wires can result in injury or death. Metal ladders, farm equipment, boat masts, construction machinery, aerial antennas , and similar objects are frequently involved in fatal contact with overhead wires. Unauthorized persons climbing on power pylons or electrical apparatus are also frequently

1705-404: Is typically a single event, but the larger peak current may flow for hundreds of milliseconds, making it considerably more energetic than negative lightning. The dielectric breakdown strength of dry air, at Standard Temperature and Pressure (STP), between spherical electrodes is approximately 33 kV/cm. This is only a rough guide, since the actual breakdown voltage is highly dependent upon

Ethiopian Electric Power - Misplaced Pages Continue

1760-560: The chest area. The voltage at which there is the danger of electrocution depends on the electrical conductivity of dry human skin. Living human tissue can be protected from damage by the insulating characteristics of dry skin up to around 50 volts. If the same skin becomes wet, if there are wounds, or if the voltage is applied to electrodes that penetrate the skin, then even voltage sources below 40 V can be lethal. Accidental contact with any high voltage supplying sufficient energy may result in severe injury or death. This can occur as

1815-493: The electrical breakdown of such insulators, causing them to act as conductors. These transferred potentials are dangerous to people, livestock, and electronic apparatus. Lightning strikes also start fires and explosions, which result in fatalities, injuries, and property damage. For example, each year in North America, thousands of forest fires are started by lightning strikes. Measures to control lightning can mitigate

1870-553: The high-voltage line but thoroughly insulated from the earth so that he is at the same electrical potential as that of the line. Since training for such operations is lengthy, and still presents a danger to personnel, only very important transmission lines are subject to maintenance while live. Outside these properly engineered situations, insulation from earth does not guarantee that no current flows to earth—as grounding or arcing to ground can occur in unexpected ways, and high-frequency currents can burn even an ungrounded person. Touching

1925-421: The state monopoly in generating electric power for the national power grid, although Ethiopia also allows Independent Power Producers to construct and to operate power plants for delivering power to the national grid since 2017. Electric power distribution and the operation of power transmission lines of ≤66 kV within the national power grid is not part of the activities of Ethiopian Electric Power, that

1980-557: The IET, such as within the PDF detailing amendment 3 to the 18th edition ( ), and is summarised below, along with some notable other events. Only major changes between editions/amendments are noted. Two core cable, line and neutral, no earth. Protection was a re-wirable fuse. Revised in 1943; reprint with minor amendments in 1945; supplement issued in 1946; revision to section 8 in 1948. Supplement issued 1954. First mention of PVC insulated cables. Reprinted with amendments in 1968 and 1969,

2035-1039: The United States, the National Fire Protection Association has published a guideline standard NFPA 70E for evaluating and calculating arc flash hazard , and provides standards for the protective clothing required for electrical workers exposed to such hazards in the workplace. Even voltages insufficient to break down air can supply enough energy to ignite atmospheres containing flammable gases or vapours, or suspended dust. For example, hydrogen gas, natural gas , or petrol/ gasoline vapor mixed with air can be ignited by sparks produced by electrical apparatus. Examples of industrial facilities with hazardous areas are petrochemical refineries, chemical plants , grain elevators , and coal mines . Measures taken to prevent such explosions include: In recent years, standards for explosion hazard protection have become more uniform between European and North American practice. The "zone" system of classification

2090-541: The appropriate method of electric wiring. The BSI ( British Standards Institute ) publishes numerous titles concerning acceptable standards of design/safety/quality across different fields. The first edition was published in 1882 as the "Rules and Regulations for the Prevention of Fire Risks arising from Electric Lighting." The title became "General Rules recommended for Wiring for the Supply of Electrical Energy" with

2145-445: The circuit to stabilize the arc's current/voltage characteristics. Electrical transmission and distribution lines for electric power typically use voltages between tens and hundreds of kilovolts. The lines may be overhead or underground. High voltage is used in power distribution to reduce ohmic losses when transporting electricity long distance. It is used in the production of semiconductors to sputter thin layers of metal films on

2200-567: The electrode shape and size. Strong electric fields (from high voltages applied to small or pointed conductors) often produce violet-colored corona discharges in air, as well as visible sparks. Voltages below about 500–700 volts cannot produce easily visible sparks or glows in air at atmospheric pressure, so by this rule these voltages are "low". However, under conditions of low atmospheric pressure (such as in high-altitude aircraft ), or in an environment of noble gas such as argon or neon , sparks appear at much lower voltages. 500 to 700 volts

2255-453: The flyback effect resulting in voltages greater than the turns ratio multiplied by the input voltage. They typically produce higher currents than electrostatic machines, but each doubling of desired output voltage roughly doubles the weight due to the amount of wire required in the secondary winding. Thus scaling them to higher voltages by adding more turns of wire can become impractical. The Cockcroft-Walton multiplier can be used to multiply

Ethiopian Electric Power - Misplaced Pages Continue

2310-528: The hazard; these include lightning rods , shielding wires, and bonding of electrical and structural parts of buildings to form a continuous enclosure. BS 7671 British Standard BS 7671 "Requirements for Electrical Installations. IET Wiring Regulations", informally called in the UK electrical community "The Regs" , is the national standard in the United Kingdom for electrical installation and

2365-525: The highest voltages they normally encounter, to be high voltage . Voltages over approximately 50 volts can usually cause dangerous amounts of current to flow through a human being who touches two points of a circuit, so safety standards are more restrictive around such circuits. In automotive engineering , high voltage is defined as voltage in range 30 to 1000 VAC or 60 to 1500 VDC. The definition of extra-high voltage (EHV) again depends on context. In electric power transmission engineering, EHV

2420-658: The isolation and discovery of the element argon from atmospheric air. Induction coils powered early X-ray tubes. Moseley used an X-ray tube to determine the atomic number of a selection of metallic elements by the spectrum emitted when used as anodes. High voltage is used for generating electron beams for microscopy . Cockcroft and Walton invented the voltage multiplier to transmutate lithium atoms in lithium oxide into helium by accelerating hydrogen atoms. Voltages greater than 50 V applied across dry unbroken human skin can cause heart fibrillation if they produce electric currents in body tissues that happen to pass through

2475-405: The plastic coating should be free of air bubbles which result in coronal discharges within the bubbles. A high voltage is not necessarily dangerous if it cannot deliver substantial current . Despite electrostatic machines such as Van de Graaff generators and Wimshurst machines producing voltages approaching one million volts, they deliver a brief sting. That is because the current is low, i.e. only

2530-448: The power supply and load allow sufficient current to flow, a self-sustaining arc may form. Once formed, an arc may be extended to a significant length before breaking the circuit. Attempting to open an inductive circuit often forms an arc, since the inductance provides a high-voltage pulse whenever the current is interrupted. AC systems make sustained arcing somewhat less likely, since the current returns to zero twice per cycle. The arc

2585-909: The revision of CENELEC Harmonization Document HD 308 S2: 2001 Identification of cores in cables and flexible cords and agrees generally with BS EN 60446 : 2000 Basic and safety principles for the man-machine interface, marking and identification. Identification of conductors by colours or numerals and BS EN 60445 : 2000 Basic and safety principles for man-machine interface, marking and identification of equipment terminals and of terminations…. The single-phase colours of red phase and black neutral are replaced by brown phase and blue neutral. These colours have been used in appliance flexible cables since 1969. The cable core colours are described in IEC 60304 (1982-01), Standard colours for insulation for low- frequency cables and wires. The three-phase phase colours are brown, black and grey instead of red, yellow and blue. Where

2640-642: The safety of electrical wiring systems. It did not become a recognized British Standard until after the publication of the 16th edition in 1992. The standard takes account of the technical substance of agreements reached in CENELEC . BS 7671 is also used as a national standard by Mauritius , St Lucia , Saint Vincent and the Grenadines , Sierra Leone , Singapore , Sri Lanka , Trinidad and Tobago , Uganda , Cyprus , and several other countries, which base their wiring regulations on it. The latest version

2695-410: The spark produced in a dry climate when touching a doorknob after walking across a carpeted floor. The voltage can be in the thousand-volt range, but the average current is low. The standard precautions to avoid injury include working under conditions that would avoid having electrical energy flow through the body, particularly through the heart region, such as between the arms, or between an arm and

2750-477: The surface of the wafer . It is also used for electrostatic flocking to coat objects with small fibers that stand on edge. Spark gaps were used historically as an early form of radio transmission. Similarly, lightning discharges in the atmosphere of Jupiter are thought to be the source of the planet's powerful radio frequency emissions. High voltages have been used in landmark chemistry and particle physics experiments and discoveries. Electric arcs were used in

2805-571: The third edition in 1897, "Wiring Rules" with the fifth edition of 1907, and settled at "Regulations for the Electrical Equipment of Buildings" with the eighth edition in 1924. Since the 15th edition (1981), these regulations have closely followed the corresponding international standard IEC 60364 . In 1992, the IEE Wiring Regulations became British Standard BS 7671 so that the legal enforcement of their requirements

SECTION 50

#1732776221757

2860-443: The victims of electrocution. At very high transmission voltages even a close approach can be hazardous, since the high voltage may arc across a significant air gap. Digging into a buried cable can also be dangerous to workers at an excavation site. Digging equipment (either hand tools or machine driven) that contacts a buried cable may energize piping or the ground in the area, resulting in electrocution of nearby workers. A fault in

2915-482: The voltage produced by an induction coil. It generates DC using diode switches to charge a ladder of capacitors. Tesla coils utilize resonance, are lightweight, and do not require semiconductors. The largest scale sparks are those produced naturally by lightning . An average bolt of negative lightning carries a current of 30 to 50 kiloamperes, transfers a charge of 5 coulombs , and dissipates 500 megajoules of energy (120 kg TNT equivalent , or enough to light

2970-610: Was again split up into two companies, Ethiopian Electric Utility and Ethiopian Electric Power . Ethiopian Electric Power was formed by Council of Ministers Regulation No.302/2013. The first (2013) CEO of Ethiopian Electric Power was Azeb Asnake , replaced in August 2018 by Abraham Belay . In 2016, Ethiopian Electric Power had more than 3500 employees. 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

3025-637: Was easier both with regard to the Electricity at Work regulations and from an international point of view. They are now treated similar to other British Standards. BS 7671 has converged towards (and is largely based on) the European Committee for Electrotechnical Standardization (CENELEC) harmonisation documents, and therefore is technically very similar to the current wiring regulations of other European countries. The historical timeline of publication can be found within documents published by

#756243