In electro engineering, ground or earth is the reference point in the electrical circuit from which the voltage is measured, the common return path for an electric current, or a direct physical connection to earth.
Electrical circuits can be connected to ground (earth) for several reasons. In electrically powered equipment, the exposed metal parts are connected to the ground so that if, due to any fault conditions, the line voltage supply connection occurs to such a conductive part, the current flow shall be such that any protective device is fitted for overload protection or "leaking" will operate and disconnect the channel voltage. This is done to prevent user-generated damage from contact with such harmful voltage in situations where the user can, at the same time, also come into contact with the object in ground/earth potential. In power distribution systems, the earth protective conductor (PE) is an important part of the safety provided by the earthing system.
The ground connection also limits static electricity accumulation when handling flammable products or static-sensitive devices. In some telegraph and electrical transmission circuits, the earth itself can be used as one of the circuit conductors, saving the cost of installing a separate return conductor (see the return of a single cable).
For measurement purposes, the Earth serves as a constant (potential) potential reference to other measurable potentials. The electrical ground system must have an appropriate current carrying capacity to be used as an adequate zero voltage reference level. In electronic circuit theory, "ground" is usually idealized as an infinite source or sink to charge, which can absorb the infinite current without altering its potential. Where real ground connections have significant resistance, zero potential forecasts are no longer valid. Stray voltage or earth potential rise effect will occur, which may cause noise in the signal or if large enough will result in an electric shock hazard.
The use of the term earth (or earth) is very common in electrical and electronic applications whose circuits in portable electronic devices such as cell phones and media players as well as circuits in vehicles can be said to have "ground" connections without actual connections to Earth, though "common" right for such connections. This is usually a large conductor attached to one side of a power supply (such as a "ground plane" on a printed circuit board) that serves as a common return path for currents of different components in the circuit.
Video Ground (electricity)
Histori
Remote electromagnetic telegraph systems from 1820 onwards used two or more cables to carry signals and reverse current. It was discovered, perhaps by the German scientist Carl August Steinheil in 1836-1837, that the soil could be used as a return path to complete the circuit, making re-wiring unnecessary. However, there is a problem with this system, exemplified by the transcontinental telegraph line built in 1861 by the Western Union Company between St. Joseph, Missouri, and Sacramento, California. During dry weather, land connections often develop high resistance, requiring water to be poured on the ground trunk to allow the telegraph to work or the phone to ring.
Later, when the phone began to replace telegraphy, it was discovered that currents on earth induced by electrical systems, electric trains, telephones and other telegraph circuits, and natural sources including lightning caused unacceptable noise to audio signals, and two cables or the 'metal circuit' system was reintroduced around 1883.
Maps Ground (electricity)
Radio communication
Electrical connections to the earth can be used as a potential reference for radio frequency signals for certain types of antennas. The part directly in contact with the earth - the "earth electrode" - can be as simple as a metal rod or earth-driven pole, or a connection to a buried metal water pipe (the pipe must be conductive). Since high-frequency signals can flow to Earth due to capacitive effects, capacitance to the ground is an important factor in the effectiveness of the signal base. Therefore, complicated systems of buried rods and wires can be effective. The ideal signal ground maintains a fixed potential (zero) regardless of how much electric current flows into the ground or out of the ground. The low impedance at the signal frequency of the electrode-to-earth connection determines its quality, and that quality is increased by increasing the surface area of ​​the electrode in contact with the earth, increasing the depth it drives, using some connected ground. stems, increases ground water content, increases the conductive mineral content of the soil, and increases the area of ​​land covered by the soil system.
Some types of transmitter antenna systems in VLF, LF, MF and lower SW range must have good soil to operate efficiently. For example, a vertical monopole antenna requires a ground plane often consisting of an interconnected cable network that runs radically away from the antenna base for distances equal to the height of the antenna. Sometimes a counterpoise is used as a ground plane, which is supported above ground.
Build cable installation
Electrical distribution systems are often connected to ground to limit the voltage that can arise in the distribution circuit. An isolated soil distribution system can achieve high potential due to transient stresses caused by curves, static electricity, or accidental contact with higher potential circuits. The ground connection of the system eliminates that potential and limits the voltage rise of the ground system.
In the installation of the power cord (power cord), the term ground conductor usually refers to three different conductors or conductor systems as listed below.
Ground-conductor equipment provides the electrical connection between the physical ground (earth) and the grounding/bonding system, which connects (bonds) parts of metal equipment which usually carry no current. According to the US National Electrical Code (NEC), the reason for doing this is to limit the voltage imposed by lightning, line spikes, and contact with high voltage channels.
Equipment bonding conductors provide a low impedance path between metal parts that do not normally carry currents and one conductor from an electrical system source. If any exposed metal part has to be energy (error), such as by frayed or damaged conductors, it creates short circuits, causing overprotection devices (circuit breakers or fuses) to open, cleanse (disconnect) errors. It is important to note that this action occurs regardless of whether there is a relationship to the physical ground (earth); the earth itself has no role in this error-cleaning process because the current must return to its source; however, its sources are very often associated with physical ground (earth). (see Kirchhoff circuit law). By binding (interconnecting) all open carrier metal objects not exposed together and with other metal objects such as pipes or structural steel, they must remain close to the same potential voltage, thereby reducing the probability of a shock. This is very important in the bathroom where one can come into contact with several different metal systems such as supply pipes and sewer and frame tools. When a system needs to be connected to the physical ground (earth), the equipment bonding conductor also becomes the grounding equipment conductor (see above).
The grounding electrode conductor ( GEC ) is used to connect a system grounding ("neutral") conductor, or equipment to a ground electrode, or point on the grounding electrode system. This is called a "grounding system" and most electrical systems must be earthed. NEC AS and BS 7371 UK list system which must be grounded. According to NEC, the purpose of connecting electrical systems to physical ground (earth) is to limit the voltage imposed by lightning events and contact with higher voltage lines, and also for voltage stabilization. In the past, the water supply pipe was used as an earthing electrode, but due to the increasing use of plastic pipe, which is a poor conductor, the actual use of grounding electrodes is required. This type of ground applies to radio antennas and lightning protection systems.
Permanently installed electrical equipment, unless unnecessary, has been permanently connected to the grounding conductor. Portable electrical appliances with metal boxes may be connected to the ground on earth with pins on the attachment plug (see power outlet and domestic AC outlet). The size of a power grounding conductor is usually governed by local or national cable regulations.
Grounding System
In the power supply system, the grounding system determines the electrical potential of the conductor relative to the Earth's conductive surface. The choice of an earthing system has implications for the security and electromagnetic compatibility of the power supply. The rules for earthing systems vary between different countries.
Functional earth connections function more than protect against electric shock, as they can carry current during normal operation of the device. Such devices include spike suppression, electromagnetic compatibility filters, multiple antenna types, and various measuring instruments. Generally the protective earth systems are also used as functional earths, though this requires care.
Laying impedance
The power distribution system can be firmly grounded, with one circuit conductor directly connected to the earth ground electrode system. Alternatively, some amount of electrical impedance can be connected between the distribution system and the ground, to limit the currents that can flow to the earth. The impedance can be either a resistor, or an inductor (coil). In high impedance grounding systems, the fault current is limited to a few amperes (exact value depends on the system voltage class); a low impedance grounding system will allow several hundred amperes to flow on an error. A large solid distribution system can have thousands of amperes of ground noise current.
In an AC polyphase system, an artificial neutral grounding system can be used. Although no phase conductor is directly connected to the ground, a specially constructed transformer (a "zig zag" transformer blocks the frequency of power flows from flowing to the earth, but allows leakage or transient currents to flow to the ground.
The low resistance grounding system uses a neutral grounding resistor (NGR) to limit the fault current to 25 A or greater. The low resistance grounding system will have a time rating of (say, 10 seconds) that indicates how long the resistor can carry a noise current before overheating. The ground disturbance protection relay must pass through the circuit breaker to protect the circuit before excessive warming occurs.
The high-resistance grounding (HRG) system uses NGR to limit the fault current to 25 A or less. They have continuous assessment, and are designed to operate with a one-ground error. This means that the system will not immediately travel on the first ground error. If a second ground fault occurs, the ground disturbance protection relay must pass through the breaker to protect the circuit. In the HRG system, the sensing resistor is used to continuously monitor the continuity of the system. If an open circuit is detected (eg, due to welding interrupted in NGR), the monitoring device will sense the voltage through the sensing resistor and the breaker trip. Without the sensing resistor, the system can continue to operate without ground protection (because open circuit conditions will cover ground errors) and more transient voltage may occur.
Uncategorized system
If the shock hazard is high, a non-heated dedicated power system can be used to minimize the possibility of leakage of current to the ground. Examples of such installations include patient care areas in hospitals, where medical equipment is directly connected to a patient and should not permit an electric current to enter the patient's body. The medical system includes a monitoring device to warn any increase in leakage current. At wet construction sites or in shipyards, isolation transformers may be provided so that faults on electrical appliances or cables do not cause the user to be exposed to an electric shock hazard.
Circuits used to feed on sensitive audio or video production equipment can be extracted from isolated power systems to limit noise injection from the power system.
Power transmission
In a single-wire earth return (AC) power distribution system (SWER), the cost will be saved only by using one high-voltage conductor for the power grid while directing the AC return through the earth. This system is widely used in rural areas where large currents of the earth will not cause harm.
Some high voltage current power transmission systems (HVDC) use soil as the second conductor. This is very common in schemes with submarine cables, because sea water is a good conductor. The embedded grounding electrode is used to make connections to the earth. The site of this electrode should be chosen carefully to prevent electrochemical corrosion in the underground structures.
Particular attention in the design of electrical substations is the potential for the earth to increase. When a very large fault current is injected into the earth, the area around the injection point can rise to high potential with respect to distant points. This is due to the limited conductivity of the earth's soil layer. The voltage gradient (changing the voltage within a certain distance) may be so high that two points on the ground may be at a very different potential, creating a danger to anyone standing on the ground in the area. Pipes, rails, or communication cables entering the substation may see different ground potentials inside and outside the substation, creating dangerous tension stresses.
Electronics
The signal area acts as a return path for signal and power (at extra low voltage, less than about 50 V) inside the equipment, and on signal interconnection between equipment. Many electronic designs display single returns that serve as a reference for all signals. Power and signals are often connected, usually through a metal box of equipment. Printed circuit board designers should be careful in electronic system layout so that high power or fast current switching in one part of the system does not inject noise to the low-level sensitive parts of the system due to some common impedance on the track layout footprint.
Landline versus earth
Voltage is measured on an interval scale, which means only a measurable difference. To measure the voltage of a point, a reference point should be selected to measure against. This common reference point is called "ground" and is considered to have a zero voltage. This signal ground may or may not be connected to the power ground. A system in which the ground system is not connected to another circuit or to the earth (though there may still be AC ​​coupling) is often referred to as a floating or double-insulated ground.
Functional reason
Some devices require connections to the Earth's mass to function correctly, as they differ from pure protective roles. Such connections are known as functional earths - for example some long wavelength antenna structures require functional earth connections, which generally should not be haphazardly connected with the earth protective supply, since the introduction of radio frequencies transmitted into power distribution networks is both. illegal and potentially dangerous. Because of this separation, purely functional soil should not be reliable for performing protective functions. To avoid accidents, such functional bases are usually associated with white or beige cables, and are not green or green/yellow.
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On television stations, recording studios, and other installations where signal quality is essential, special signal ground known as "technical ground" (or "technical earth", "earth-specific" and "audio earth") is often installed, to prevent ground loop. This is essentially the same as AC power ground, but no common grounding device wires are allowed to plug it in, as it may carry electrical noise. For example, only audio equipment is connected to a technical ground in a recording studio. In most cases, metal studio equipment racks are all joined together with heavy copper cables (or flattened copper or busbar pipes) and similar connections are made to technical ground. Carefully taken that no ground chassis device is placed on the shelf, since the grounded AC connection to the technical ground will undermine its effectiveness. For highly demanding applications, the main technical areas may consist of heavy copper pipes, if necessary with drilling through multiple concrete floors, so that all technical bases can be connected to the shortest possible path to the grounding ground in the basement.
Lightning protection system
The lightning protection system is designed to reduce the effects of lightning through connections to large grounding systems that provide large surface area connections to the earth. A large area is required to dissipate a large current of lightning strikes without damaging the conductor of the system with excess heat. Because lightning strikes are energy pulses with very high frequency components, grounding systems for lightning protection tend to use short straight operations to reduce self-inductance and skin effects.
Bond
Strictly speaking, the term grounding or grounding is meant to refer to the electrical connection to the ground/earth. Bonding is a practice that deliberately connects metal items that are not designed to carry electricity. It brings all goods bound to the same electrical potential as protection from electric shock. The bound goods can then be connected to the ground to bring them to Earth's potential.
Soil bend (earth)
In an electrical substation the ground mat (ground) is a mesh of conductive material mounted in places where a person will stand to operate a switch or other equipment; it is attached to the local support metal structure and to the handle of the switchgear, so the operator will not be exposed to high differential voltage due to error in the substation.
Around electrostatic sensitive devices, ground or ground mats (earthing) are used to ground static electricity generated by people and mobile equipment. There are two types used in static controls: Static Dissipative Mats, and Conductive Mats.
A static dissipative mat based on a conductive surface (usually a case of a military facility) is usually made of 3 layers (3-layers) with a static dissipative vinyl coating that surrounds a conductive substrate that is electrically bonded to the ground (earth). For commercial use, static disipative rubber mats are traditionally used made of 2 layers (2-layers) with a resistant electrically resistant sealable coating that makes it last longer than vinyl mats, and conductive rubber floor. Conductive mats are made of carbon and are only used on the floor for the purpose of drawing static electricity to the ground as quickly as possible. Usually conductive mats are made with bearings to stand and are called "anti-fatigue" mats.
For static dissipative mats to be properly grounded, they must be attached to the ground path. Usually, both the wrist and the wrist strap are connected to ground using a common ground point system (CPGS).
In computer workshops and electronic manufacturing workers should be grounded before working on sensitive devices that can be produced by humans. For that reason, static dissipative mats can and also be used on the production assembly floor as "floor runners" along the assembly line to attract static generated by people walking up and down.
Isolation
Isolation is the mechanism that overcomes the foundation. These devices are often used with low-power consumer devices, and when electronic engineers, hobbyists, or repairmen work on circuits that are typically operated using a power line voltage. Isolation can be achieved simply by installing a "1: 1 wire ratio" transformer with the same number of turns between the device and the regular power service, but applies to all types of transformers using two or more electrically insulated winds to each other.
For an isolated device, touching a powered conductor does not cause a great shock, because there is no way back to another conductor through the ground. However, shock and electric shock may still occur if the two poles of the transformer are contacted by bare skin. Previously it was suggested that repairmen "work with one hand behind their back" to avoid touching two parts of the device being tested at the same time, thus preventing circuits from crossing the chest and disrupting the heart rhythm/causing cardiac arrest.
Generally every power line transformer acts as an isolation transformer, and each step up or down has the potential to form an isolated circuit. However, this isolation will prevent the failed device from blowing the fuse when it is shortened to its ground conductor. The isolation that can be made by each transformer is defeated by always having one leg of the earthed transformer, on both sides of the input and output coil of the transformer. The power lines also typically eart one special wire at each pole, to ensure equal distribution of currents from the poles to the poles in case of short surfaces.
In the past, grounded equipment has been designed with internal isolation to the extent that it allows simple ground cutting by the cheater connector without any obvious problem (dangerous practice, since the security of the floating equipment generated depends on the insulation in the power transformer). Modern equipment but often includes power entry modules designed with intentional capacitive coupling between AC power lines and chassis, to suppress electromagnetic interference. This produces significant leakage current from the power line to the ground. If the ground is disconnected by the cheater connector or by accident, the resulting leakage current may cause mild shock, even without any error on the equipment. Even small leakage currents are a significant problem in medical settings, because accidental ground termination can introduce these currents to the sensitive parts of the human body. As a result, the supply of medical personnel is designed to have low capacitance.
Class II devices and power supplies (such as cell phone chargers) do not provide any ground connections, and are designed to isolate output from input. Security is ensured by double insulation, so two insulation failures are required to cause a shock.
See also
Note
References
- Federal Standard 1037C to support MIL-STD-188
External links
- Ground Circuit and Grounding Practices
- Electrical Safety chapter of Lessons in Vol 1 DC series of books books and series.
- Grounding for Low and High Frequency Circuits (PDF) Ã, - Analog Devices Application Notes
- User's Guide IC Amplifier for Splitting, Grounding, and Making the Right Things for Change (PDF) Ã, - Analog Devices Application Notes
- Electromagnetic Telegraph, by J. B. Calvert
Source of the article : Wikipedia
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