Grounding

from Wikipedia, the free encyclopedia

The ground is the totality of all the means and measures for grounding, that is, for the discharge of electrical currents in the ground or the soil .

Earthing is referred to as open if overvoltage protection devices, e.g. B. Protective spark gaps in which the grounding line is built.

Since the earthing and equipotential bonding of a building are usually connected to one another, the term earthing is often (imprecisely) even when equipotential bonding or lightning protection systems are actually meant.

Earth symbol
"Ground before use" pictogram according to DIN EN ISO 7010

Basics

The term earth refers to the ground on the one hand and the electrical potential of the conductive soil on the other. For personal protection , it consists of earth electrodes , protective conductors , protective conductor terminals or lightning rods . The area that lies outside the effective range of an earth electrode is called reference earth or neutral earth . If no noticeable voltages caused by the grounding current occur between the grounding and an arbitrarily selected grounding point, this selected grounding point is in the area of ​​neutral ground.

Foundation earth connection with equipotential bonding rail in a residential building

The aim of earthing is to create a defined reference potential or equipotential bonding by means of which a potential voltage is to be short-circuited . However, since the earthing has a resistance like any other electrically conductive connection , the so-called earthing resistance , a voltage remains in the case of a permanent current flow according to Ohm's law . It can therefore only be assumed in static applications that the grounding eliminates any potential difference.

The basic terms for earthing systems in connection with low-voltage systems are specified in DIN VDE 0100-200: 2006-06 "Setting up low-voltage systems" in main section 826-13 - "Earthing and connections". This standard largely contains the German translation of IEC 60050-826: 2004 with minor national adjustments. The term definitions can also be queried via the freely accessible ELECTROPEDIA portal in "Section 826-13" in 12 languages ​​(or translated into any of the languages ​​offered).

Grounding types

Depending on the task and structure, there are four different types of grounding in electrical engineering:

The protective earthing creates a secure connection between electrical systems and devices to the ground, so that dangerous contact voltages are avoided in the event of a faulty device function . The protective earth can also serve as a functional earth, but not the other way around.

The functional earth is used to operate electrical equipment safely. Functional grounding is used to safely divert interference currents and avoid electrical interference.

The lightning protection earthing is intended to safely discharge the lightning current into the ground in order to protect buildings.

The operational earthing is mainly used in power plants and switchgear and is intended to ensure trouble-free operation of the system or the devices.

In many cases, groundings are also combined and meshed with one another.

Functions of the grounding system

Earthing strap at the foot of a high-voltage pylon

The earthing system (earthing) comprises all measures required to connect an electrical part to the earth and is an essential part of both low-voltage and high-voltage networks. In new buildings, the earthing system is the first technical device that has to be installed. The earthing system consists of the earthing cables and one or more earth electrodes. Depending on the installation depth, the respective earth electrodes are divided into deep earth electrodes that are driven vertically into the ground and surface earth electrodes that are laid horizontally. Foundation earth electrodes are a special form of surface earth. They are laid in the foundation below the moisture insulation.

Foundation earth electrode in the excavation of a single-family house

The task of the respective earthing system is:

  • Protection of living beings by limiting the touch voltage and the step voltage
  • Lightning protection of plants and buildings
  • Proper function of the power supply
  • Limiting electromagnetic interference

The respective earthing systems are designed and installed according to these requirements. Certain requirements have to be met when designing the earthing system:

  • Personal security
  • Corrosion resistance
  • Mechanic solidity
  • Control of the highest fault current and its thermal effects

When installing the earthing system, the designer must consider both the nature of the ground and the level of the expected fault currents.

Examples

Elimination of influences

Due to high- voltage systems , neighboring lines or other conductive objects can be subject to ohmic, inductive or capacitive influence, which creates voltages that interfere with electrical systems or devices, or - with sufficient current - can even be dangerous for people. This form of the influence of heavy currents can be (largely) compensated for by earthing part of the transformer star point or inductive earthing.

Personal protection

People and other living beings are at risk if they touch two electrically conductive objects between which there is a dangerously high electrical voltage. In high and low voltage networks, all conductive parts of electrical consumers that are not under voltage during operation (e.g. housing parts) are therefore connected to the earth potential via the so-called protective conductor . This grounding method is protective grounding. The connection of an outer conductor to these objects then leads to a ground fault , which can trigger the overcurrent protection device and thus cut off the voltage.

Explosion prevention

Groundings for explosion protection are similar to measures for ESD protection and protect people and property.
When filling z. B. from tankers, trucks, wagons, barrels, big bags (English for large sack or bulk material container ) etc. electrostatic charges arise . Earthing devices prevent sources of ignition from electrostatic charges. Earthing devices are, for example, earthing clamps that are clamped to the object to be earthed (it is important to ensure that the “teeth” of the clamp really get through the paint and onto the metal, for example in the case of a barrel) and are connected to an earth electrode by means of a cable . This prevents sparks from forming and an explosion from occurring in an Ex atmosphere.

Mobile generating sets

The so-called earthing spike is an accessory part of a mobile power generator . If its generator cannot be connected to an earth electrode available on site, this up to one meter long copper rod is driven into the ground and connected to the generator system. Modern generator systems usually do not need an earthing spike if they are operated as an IT system with an insulation monitor.

Grounding an overhead line

Maintenance / occupational safety

Before working on electrical systems with dangerous voltages, for example on distributors , overhead lines or overhead lines, it is mandatory to switch off the voltage and then to earth all electrical conductors. In the event of an unintentional switch-on , the grounding causes a short circuit that triggers the fuse and thus cuts off the voltage. In addition, any charge that may still be present can be discharged from the system via the grounding , for example when working on high-voltage lines.

It is only permissible to refrain from doing this in exceptional cases and only for specially trained electricians , for example when working under voltage .

Earthing rod for maintenance work in tram construction

Lightning protection

The lightning protection is designed to protect people and property.

Lightning protection systems reduce the risk of damage from lightning strikes in buildings and, for example, on overhead lines . They consist of interception systems, down conductors, earthing and lightning protection equipotential bonding . Air-termination systems are placed at all points that can be struck by lightning. The down conductors conduct the lightning current from them to the earthing system. In the event of a lightning strike, surge protection devices create equipotential bonding between all electrical conductors and the earthed protective conductor for conducted overvoltages. Such line-bound overvoltages can arise despite lightning protection due to the influence of the high field gradients or due to magnetic coupling of the lightning currents in supply and signal lines.

Railway earth

Under the railway ground , the grounded rails are of webs , which originate from single-pole overhead lines are used as a return line. This customary construction is inexpensive, but due to the large distance between the lines, it causes a large magnetic field and is therefore unfavorable from the point of view of electromagnetic compatibility . Due to the different local and ground conditions, there are different grounding concepts in Europe. The newer name for the rail earth is connection with the return line .

There are different grounding concepts for DC and AC railways. The return line systems of direct current railways must be galvanically separated from other earthed parts. In order to improve the return conduction, earth cables are often laid parallel to the railway line as additional return conductors.

ESD protection

To prevent electrostatic discharge ( discharge electrostatic - short ESD) become the ground of persons and used for potential equalization grounding straps, table mats and tools with dissipative handles. This is always necessary when electronics or electronic components are handled or assembled. In particular, diode lasers , field effect transistors , but also Schottky diodes , light emitting diodes and most other active electronic components and integrated circuits are at risk if they are improperly handled, transported or soldered into circuit boards or if corresponding assemblies are touched.

The conductive connections between the person, the device and the earth reduce voltage differences that could be dangerous to the components. The ESD sensitivity of electronic components is tested with the human body model and specified in ESD sensitivity classes.

see also: Antistatic tape

High voltage direct current transmission

In some monopolar systems for high-voltage direct current transmission , the highly conductive seawater is used as the second pole, if available. Extensive grounding electrodes are required on land. Earthing is important for the function, but it must also take into account aspects of personal protection. Grounding by connecting the pole to be grounded to any objects in the converter station is prohibited for reasons of electrical corrosion and undesirable effects on electrical systems, for example through biasing of transformers and stray direct currents. This is why systems for high-voltage direct current transmission are earthed at a suitable location - if available in the sea - usually a few kilometers away from the converter station.

If the grounding is done on land, several graphite electrodes are usually buried for anodes . A copper ring is laid in the ground for cathodes . For electrodes in the sea, graphite electrodes or titanium meshes are used for anodes. A bare copper ring on the sea floor with a diameter of over 100 m is usually used for cathodes. In the case of onshore earthing systems such as that of the Pacific DC Intertie in Celilo, the earth electrode is located 10 km from the converter station in the form of a metallic iron ring with a diameter of over 3 km in the ground. To avoid electrolysis , which would destroy the metallic grounding electrode, the metallic iron ring is embedded in petroleum coke , which establishes electrical contact with the surrounding soil.

The location of such electrodes must be carefully selected with regard to the possible risk of corrosion to other metallic parts in the ground, such as pipes or the effects on electrical systems. In the case of high-voltage direct current transmission systems with submarine cables, it should not be too close to the cable route, as otherwise stray currents can flow away through the cable sheath, which can lead to corrosion.

Radio technology

Antennas require grounding in order to improve their function , especially when the radio waves to be transmitted or received are long . Antennas that are exposed on or on roofs must also be earthed to ensure lightning protection. This protects people and connected devices from damage. In the case of asymmetrically constructed antennas (e.g. ground plane antenna ), high-frequency grounding is necessary for the antenna to function. The high-frequency grounding of an antenna offers the equalizing currents a low-resistance current path and is often called the counterweight of the antenna. Particularly complex earthing systems are found in transmission systems for long wave , medium wave and long wave , because the efficiency of such systems depends crucially on the low resistance of the earthing at the operating frequency of the radio system. In the case of transmission systems for long wave, medium wave and long wave, several metal bands are buried around the antenna location at a shallow depth (10 to 50 centimeters), which run away radially from the antenna center. If the ground does not allow burying, these may be laid above ground on small masts. These earth bands should be at least as long as the antenna support is high. In most cases a value of a quarter of the emitted wavelength is sufficient, but earth bands with a length of 1.5 times the emitted wavelength have already been laid. Such a system is called an earth network . If the antenna carrier is on a platform in the sea, there is no need for an earth network because of the good conductivity of the sea water. This also applies to long, medium and long wave transmitters on board ships. For long-wave transmitters with particularly low frequencies, such as the Sanguine and ZEVS , a ground dipole is used that is grounded via a deep earth rod. In these systems, the earth electrodes are sunk several meters deep.

Functional ground

The functional earthing of audio amplifiers or signal sources is used to avoid interference signals received via electrical interference fields by connecting their metal housings to one another and to the earth potential. Oscilloscopes and other devices such as computers often have a galvanic connection between the signal ground and the protective conductor of the feeding mains connection in order to reduce interference or radiated interference. For this purpose, the housing and signal ground of other devices are often only connected to the protective conductor via an RC element .

Connections for functional earth or ground connection do not have to be marked like protective earth connections and must not be used as protective earth connections.

Grounding problems

Separate railway earth and water earth

Due to the large number of different earthing systems, the earthing systems can influence one another. This is particularly noticeable in urban areas with densely built-up areas, when railway lines run close to the built-up areas. The traction current can be superimposed on the three-phase network by potential transfers. This means that systems no longer function properly. In the worst case, these superimpositions can damage the earth electrode or even destroy the PEN conductor . Stray direct currents in the vicinity of direct current railways lead to severe corrosion on earth electrodes made of hot-dip galvanized steel.

Today's pipelines have thinner walls than before and may be sensitive to electrolytic corrosion , which occurs when a current flows through the pipeline, especially if it is an alternating current. Today it is no longer permissible to use pipelines as an earth electrode, as was the case in the past.

In order to avoid the entry of potential differences from the ground, buildings should only be earthed at a single point since 2010. If a conductive pipe is introduced into the building from the outside, an insulated pipe connection should be provided at the house connection .

exam

The presence of a connection to a potential earth alone does not guarantee reliable earthing. After setting up a potential earth, it is therefore necessary to test the discharge of fault currents in accordance with VDE 0100, for example by measuring the earth resistance .

Norms

  • DIN 18014: Foundation earth electrode - General planning principles.
  • DIN VDE 0100-200: Setting up low-voltage systems - Part 200: Terms.
  • DIN VDE 0100-410: Setting up low-voltage systems - Part 4-41: Protective measures - Protection against electric shock.
  • DIN VDE 0100-444: Setting up low-voltage systems - Part 4-444: Protective measures - Protection against interference voltages and electromagnetic interference.
  • DIN VDE 0100-540: Erection of low-voltage systems - Part 5-54: Selection and erection of electrical equipment - Earthing systems, protective conductors and protective equipotential bonding conductors.
  • DIN VDE 0141: Earthing for special high-voltage systems with nominal voltages above 1 kV.
  • DIN VDE 0151: Materials and minimum dimensions of earth electrodes with regard to corrosion.
  • DIN VDE 0185-305-3: Lightning protection - Part 3: Protection of structures and people.
  • DIN VDE 800-2-310: Application of measures for equipotential bonding and earthing in buildings with information technology equipment.

literature

  • Gerhard Kiefer, Herbert Schmolke: VDE 0100 and practice, guide for beginners and professionals . 14th edition. VDE Verlag GmbH, Berlin and Offenbach 2011, ISBN 978-3-8007-3190-9 .
  • Wilfried Knies, Klaus Schierack: Electrical systems engineering; Power plants, networks, switchgear, protective devices. 5th edition, Hanser Fachbuchverlag. 2006 ISBN 978-3-446-40574-5
  • ABB switchgear manual. On-line

Web links

Commons : Grounding  - collection of pictures, videos and audio files
Wiktionary: grounding  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ Definition according to DIN VDE 0100-200: 2006-06 section 826-13-03. earth , Verb: Establishing an electrical connection between a given point in a network, in a system or in a piece of equipment and the local earth (IEV 1 95-01-08)
  2. ↑ old definition according to DIN VDE 100-200: 1993-11 section A.5.2. No longer defined in the current edition as a single event in main section 826-13 "Earthing and connection"
  3. ↑ Werner Hörmann, Bernd Schröder: VDE series 140; "Protection against electric shock in low-voltage systems", commentary on DIN VDE 0100-410: 2007-06 . 4th edition. VDE Verlag GmbH, Berlin and Offenbach 2010, ISBN 978-3-8007-3112-1 , p. 24 .
  4. ^ Wilhelm Rudolph: VDE series 39; "Introduction to DIN VDE 0100", electrical systems in buildings . 2nd Edition. VDE Verlag GmbH, Berlin and Offenbach 1999, ISBN 3-8007-1928-2 , p. 151 .
  5. ↑ State Environment Agency North Rhine-Westphalia: Explanation of terms. (Accessed March 12, 2013) (PDF; 129 kB)
  6. ↑ Diploma thesis Johann Frei: Measurement of the impedance of extensive earth systems online (accessed on August 27, 2012; PDF; 2.9 MB)
  7. ^ Klaus Heuck, Klaus-Dieter Dettmann, Detlef Schulz: Electrical energy supply. 7th edition, Friedrich Vieweg & Sohn Verlag, Wiesbaden, 2007, ISBN 978-3-8348-0217-0
  8. ↑ Area: ELECTROPEDIA; Area 826: Electrical installations (Retrieved March 12, 2013)
  9. ↑ a b c Herbert Schmolke: Equipotential bonding, foundation earth electrodes, risk of corrosion. 7th completely revised edition, VDE Verlag GmbH, Berlin Offenbach 2009, ISBN 978-3-8007-3139-8
  10. ↑ ABB leaflet: Connection and meshing of earthing systems (accessed on December 28, 2011; PDF; 57 kB)
  11. ↑ a b c DEHN + Söhne GmbH + Co.KG .: Blitzplaner. 2nd updated edition, Neumarkt 2007. ISBN 978-3-00-021115-7
  12. ↑ Réne Flosdorff, Günther Hilgarth: Electrical Distribution. 4th edition, Verlag BG Teubner, 1982, ISBN 3-519-36411-5
  13. ↑ Mains Quality Guide: Systematic Earthing. Volume 6.1; German Copper Institute Leonardo Power Quality Initiative ( Memento of the original from January 26, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (accessed on December 28, 2011)  @1@ 2Template: Webachiv / IABot / www.leonardo-energy.org
  14. ^ Friedrich Kießling, Peter Nefzger, Ulf Kaintzyk: Overhead lines. 5th edition, Springer-Verlag, Berlin Heidelberg New York 2001, ISBN 3-540-42255-2
  15. ↑ Klaus Heuck, Klaus-Dieter Dettmann, Detlef Schulz: Electrical energy supply: generation, transmission and distribution of electrical energy for study and practice . Springer-Verlag, 2013, ISBN 978-3-8348-2174-4 , pp. 613 ( limited preview in Google Book Search [accessed December 23, 2016]).
  16. ↑ Winfried Hooppmann: The intended electrical installation practice. 3rd edition, Richard Pflaum Verlag GmbH & Co. KG, Munich, 2007, ISBN 3-7905-0885-3
  17. ↑ Employer's liability insurance association information BGI 867: Instructions for selecting and operating replacement power generators on construction and assembly sites.
  18. ^ Christoph Rützel: Railway earthing and return current conduction . In Eisenbahn-Unfallkasse (EUK) (ed.): Bahn Praxis Spezial, 11th 2007, Bahn Fachverlag GmbH, 55013 Mainz, Printing and Design Master Printing, pp. 125–128
  19. ^ Christian Budde: Comparison of the rail grounding concepts of different 16.7 Hz railways . In Eisenbahn-Unfallkasse (EUK) (ed.): Bahn Praxis Spezial E1, 2007, Bahn Fachverlag GmbH, 55013 Mainz, Printing and Design Master Printing, pp. 3–5
  20. ↑ a b Swiss Association of Road and Transport Experts : Earthing Manual. Railway technology regulations, Bern 2008
  21. ↑ Deutsche Telekom instruction sheets earthing in telecommunications systems ( Memento of the original from February 27, 2012 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (accessed on August 27, 2012; PDF; 2.3 MB)  @1@ 2Template: Webachiv / IABot / www.training.telekom.de
  22. ↑ General earthing recommendation Brüel & Kjaer Vibro GmbH (accessed on December 28, 2011; PDF; 962 kB)
  23. ↑ High-voltage tester HP5000 operating instructions Buerger Electronic ( Memento of the original from March 4, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (accessed on August 27, 2012; PDF; 446 kB) @1@ 2Template: Webachiv / IABot / buerger-electronic.de
  24. ↑ Wv Baeckmann, W. Schwenk: Handbook of cathodic corrosion protection. 4th completely revised edition, WILEY-VCH GmbH, Weinheim 1999, ISBN 3-527-29586-0
  25. ↑ Dehn + Söhne: Corrosion damage to earthing systems. In: Elektropraktiker 8/2010, special edition no. 73 Online ( Memento of the original from July 1, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (accessed on December 28, 2011; PDF; 421 kB) @1@ 2Template: Webachiv / IABot / www.dehn.de
  26. ↑ Karl-Heinz Otto, Ronald Fischer: Electrically caused corrosion . Online (accessed December 28, 2011; PDF; 263 kB)
  27. ↑ Dr.-Ing. Bodo Appel: How incorrect earthing leads to corrosion in water pipes. , In: Haustec.de, January 25, 2018
  28. ↑ VDE regulations ( Memento of the original dated February 27, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (accessed on August 27, 2012; PDF; 204 kB)  @1@ 2Template: Webachiv / IABot / www.kometec.de