Earth electrode (electrical installation)

A grounding electrode , also known as a grounding electrode , is an uninsulated, electrically conductive element of a grounding system that is located below the surface of the earth as a linear electrical contact surface. The earth electrode should have a good electrical connection to the ground in order to conduct electrical currents there.

The International Electrotechnical Dictionary defines the earth electrode as a "conductive part that is embedded in the ground or in another specific conductive medium, for example concrete or coke, which is in electrical contact with the earth." (In Germany, coke has as a medium no meaning for embedding earth electrodes).

Earth species

Earthing strap at the foot of a high-voltage pylon

Natural earth electrodes are components that can divert electrical currents into the ground, but have not been introduced into the ground for this purpose. Natural earth electrodes are z. B. metallic pipelines and structural elements made of concrete with steel reinforcement. Until the end of the 1980s, it was permissible to use metallic water pipes as protective earth. This required the approval of the utility company. Due to the negative effect of the current flow on the pipelines ( corrosion ) and the possible later replacement by plastic pipes, the use of water and gas pipes as earth electrodes according to DIN VDE 0100-540: 2012-06 Section 542.2.3 and ÖVE / ÖNORM E 8001- 1: 2010-03 Section 16 expressly prohibited.

As artificial earth electrode is any facilities that are introduced solely for the purpose of grounding into the ground. Foundation earth electrodes are connected to the steel reinforcement of the building foundation as natural earth electrodes, but are considered as artificial earth electrodes according to DIN.

Earth rods are usually in the form of stainless steel driven -Staberder from round steel, tube or other profile steels with a ram or by vibration of an electric or pneumatic impact hammer vertically into the ground. They should reach a depth of at least 9 m in the moist soil. If the depth is too small, there is poor potential distribution and thus an increased step voltage on the earth electrode in the event of a lightning strike. If the subsoil allows, deep earth rods are usually driven up to 30 meters into the earth. The permanent connection to the groundwater is advantageous. Deep earth electrodes are not suitable for high frequency applications because of the skin effect .

Surface earths are earths that are laid at a shallow depth of at least 0.5 meters parallel to the earth's surface. They are preferred when there is a moist, highly conductive soil layer at the level of the installation. Surface earths usually consist of tape materials, round materials or ropes and are put together to form meshes. The disadvantage is that the resistance to spreading is subject to greater fluctuations due to the changing soil moisture.

Foundation earth electrodes are embedded in the concrete of the foundation foundation of a building. Since the conductivity of the concrete is often lower than that of the ground, the grounding straps inserted in reinforced concrete foundations are connected to the reinforcement at regular intervals.
If the foundation is isolated from the ground by sealing or insulating layers, the foundation earth electrode is installed below the insulating layer and, if necessary, embedded in the cleanliness layer. Alternatively, a ring earth electrode can be laid around the foundation of the structure, which may be connected through under the foundation to maintain the intended mesh size .

Earth forms

Cuff that is placed around metallic pipelines and tensioned to connect the equipotential bonding.

The way the earth electrode is laid has a great influence on the potential behavior. Horizontally laid earth electrodes should be designed as ring earth electrodes if possible . If it is not possible to use a foundation earth electrode, the ring earth electrode (on the edge of the excavation) can be led around the foundation of the structure.

There are also the following earth forms:

Rod earthing rods are pipes or round bars that are driven vertically into the ground. The individual earth rods can be inserted into one another and are connected to one another when hammered. Rod earthing rods are preferred in densely built-up areas, as other earthing rods often cannot be used there due to the lack of space. Earth rods, which are only used temporarily as construction site earth electrodes, often consist of a 1 - 1.5 m long, cross-shaped metal profile that is hammered into the ground.
Straight-line earth electrodes are often placed in the ground when cables are being laid , as the trench is then already there. To improve the resistance to spreading, strip earthing is buried upright in the ground.
According to Swiss guidelines, linear or radiation earth electrodes may be a maximum of 15 m long.
Radiant earth electrodes are made from several horizontally stretched earth electrodes, which are laid radially around a point and connected to one another. In the ideal case, 6 beam earth electrodes are laid so that the angle between two beams is 60 °. A sixfold beam earth electrode has a smaller expansion resistance compared to a ring earth electrode with the same expansion.
Meshed made of mesh-shape laid and interconnected at the ends earth electrodes. The simplest form of a mesh earth electrode is a radiation earth electrode, in which the radiation ends are connected to a ring earth electrode. In order to achieve greater constancy of resistance, several deep earth electrodes are often additionally provided and electrically conductively connected to the mesh earth electrode.
Plate earthing consists of 3 mm thick sheet steel or sheet copper plates. The copper sheet is usually perforated. The plate surface is at least 0.5 m². Plate earths are used both as surface earths and as deep earths. However, they are only used very rarely; their use is limited for special cases such as B. Telecommunication systems.

Earthen material

Since earth electrodes are laid in the ground and are subject to a certain degree of self-corrosion, they are made of corrosion-resistant materials. Sufficiently corrosion-resistant earth electrodes ensure reliable earthing for at least ten years. The earthen materials used are:

Hot-dip galvanized steel is suitable for embedding in concrete as well as in almost all types of soil. Most earth electrodes are made from hot-dip galvanized steel. The zinc coating is at least 70 micrometers.

In the case of steel earth rods with a copper layer (copper-plated steel), the minimum amount of copper layer is 20% of the steel weight.

Copper is very resistant in the ground and is used as an earth electrode for earth electrodes in high-voltage systems: In addition to earth electrodes made of pure copper, those with galvanic coatings made of tin, zinc or lead are also used.

Stainless steel earth electrodes are increasingly used, especially in larger cities, near underground trains and trams with direct current drives, as these cause corrosion by earth currents. Certain high-alloy stainless steels according to DIN 17440 are suitable, e.g. B. Material No. 1.4571. The steel should contain at least 16% chromium, 5% nickel and 2% molybdenum. If the stainless steel can form a passivated layer in the ground through the ingress of oxygen, it is just as corrosion-resistant as copper.

The geometric dimensions of the earthing material are determined in networks with a nominal voltage of more than 1 kV with low-ohmic neutral point earthing by the required current carrying capacity of the earthing. The cross-sections depend on the material the earth electrode is made of and must be selected in accordance with VDE 0101 Appendix A. In addition, DIN VDE 0141 (earthing for special high-voltage systems with rated voltages above 1 kV) must be observed.

The minimum cross-sections or minimum diameters of the earthing rod are, depending on the material:

Hot-dip galvanized steel (strip or profile including plates) 90 mm²
Hot-dip galvanized tube 25 mm in diameter
Hot-dip galvanized round rod for earth rods 16 mm in diameter (approx. 200 mm²)
Hot-dip galvanized steel cable or round wire 10 mm in diameter (approx. 80 mm²) or two times 8 mm in diameter, e.g. B. for surface and foundation earth electrodes
Copper-plated steel 50 mm²
Copper tape 50 mm²
Copper ropes (strand Ø min. 1.7 mm) or copper rods 35 mm²

The minimum dimensions for galvanized steel strip are 30 mm × 3.5 mm or 25 mm × 4 mm. A minimum diameter of 10 mm is required for round steel.

corrosion

With combined earth electrodes made of different materials, e.g. B. hot-dip galvanized steel earthing with copper earthing or with foundation earthing made of non-galvanized steel, there can be strong corrosion phenomena on the less noble earth in a moist environment due to the formation of elements or anodic corrosion ( electrolysis ) if compared to a connected earth made of noble metal or against the soil there is a clear shift towards more positive potentials. The lifespan of hot-dip galvanized earth electrodes can be e.g. B. decrease to less than five years.

In particular, earth electrodes made of (galvanized) steel are at risk, as these usually develop a negative potential compared to earth electrodes made of copper, stainless steel and earth electrodes enclosed in concrete, whereby they experience electrolytic material removal as an anode.
If a steel earth electrode is used in a copper jacket, it must be ensured that the steel is completely enclosed by the copper, as corrosion increases at small defects.
An earth electrode made of steel strip or steel cable cast in reinforced concrete is to be connected to the reinforcement every five meters.
Erdei guides (galvanized) steel should cm in the range of 30 above and below the surface to be protected against corrosion (for example by waterproof butyl - rubber tape or heat shrink tubing ). Corrosion protection is also required for connection lines running in the ground to the foundation earth electrode.
Alternatively, stainless steel can be used in these endangered areas. A material change to a less noble earth electrode in concrete is not a problem and according to VDI 0151 [3], even when laying in the ground, stronger corrosion of an earth electrode made of galvanized steel is only to be expected if the surface of the more noble material is significantly larger than that of the less noble material .
In all other cases, however, it is recommended to make the joints of various metals above ground.

If a foundation earthing is connected to a buried earthing rod, the buried earthing rod should be made of bare copper.

If lightning protection earths have a more negative potential than the rest of the earthing system, they can be protected from corrosion by isolating spark gaps.

Earth insert

Earth electrodes are used for various tasks. According to the task one differentiates:

Protective earth
Operational earth , in the home or operational power grid also Anlagenerder called
Lightning protection earth
Control earth
Auxiliary earth

One or more rod electrodes are usually used as protective earth. Foundation earth electrodes are used for new buildings.

The design of service earths is quite extensive. Since the high earth currents, especially with deep earths, result in high step voltages around the earth. Mesh earth electrodes are often used here, as these earth electrodes have low step potentials. Ring earth electrodes are used wherever mesh earth electrodes cannot be used. A variant that is also used is rod earths with additional control earths.

Particularly complex earth electrodes are used in HVDC systems and transmitters for frequencies below 3 MHz. In the former case, earth electrodes are occasionally sunk in the sea, in the latter case several bare metal strips are laid around the transmitting antenna, which is called an earth network .

Ring earth electrodes are often laid in the ground at a distance of one meter from the building to be protected as lightning protection earth.

Control earths are earths that are mainly used for potential control due to their shape and arrangement . Achieving a certain expansion resistance is of secondary importance with control earths. Ring earth electrodes, which are laid around main earth electrodes, are generally used as control earth electrodes. The control earths are laid around the main earth electrode in such a way that the outer control earths are laid lower than the inner ones. All earth electrodes are electrically connected to one another via the main earth rail.

Auxiliary earth electrodes are usually about 1 meter long, conically shaped rod earth electrodes that are required for earth measurements . The length of the earth electrode varies depending on the nature of the soil. The auxiliary earth rods are either inserted into the ground as grounding stakes or screwed into the ground with a wood screw thread at the top. For the measurement, the auxiliary earth electrodes are brought into the ground at a greater distance (40 m) from the main earth electrode and removed again after the measurement.

Ground installation in the ground

For the installation of surface earthing and plate earthing in the ground, the grown soil is lifted out and after the installation of the earthing rod it is grouted again or tamped down. The disadvantage of these earth electrodes is that the exact resistance to propagation can only be measured after the ground has been set.

Deep earth rods are hammered into the ground using a ramming device. The individual earth rods have a length of 1 to 1.5 meters and are inserted into one another. When the bars are driven in, they connect with each other independently. Greater durability is achieved if the iron rods carry a parallel copper cable with them when they are driven in, as this is less prone to corrosion and the iron also acts as a sacrificial electrode. Plate earths buried at greater depths are also known as deep earths.

Electrical Properties

The electrical properties of the grounding depend on the following factors:

Earth resistance
Design of the earth electrode

The earth resistance is made up of the propagation resistance and the resistance of the earth electrode and the earth line. Since the resistance is much smaller than the propagation resistance , it is neglected in the practical calculation. The expansion resistance is thus composed of the specific earth resistance and the dimensions and the arrangement of the earth electrode. ${\ displaystyle R_ {D}}$ ${\ displaystyle R_ {L}}$ ${\ displaystyle R_ {L}}$ ${\ displaystyle R_ {D}}$

The specific earth resistance is the resistance of one cubic meter of earth in the form of a cube with an edge length of one meter. The unit of measurement for the specific earthing resistance is The specific earthing resistance depends on the type of soil, the condition of the soil and the moisture content of the soil. ${\ displaystyle \ mathrm {\ Omega} m}$

Since the moisture content in the soil fluctuates, the calculation of the earth resistance can only be carried out with moderate accuracy. The calculation of the expansion resistance is therefore only a rough plan for practice and is checked by subsequent earth measurements.

The expansion resistance for tape earth electrodes can be determined using the following formula.

{\ displaystyle \ mathbb {R} _ {\ text {A}} = {\ frac {\ rho _ {E}} {\ mathrm {\ pi} \ cdot l}} \ cdot \ ln {\ frac {2 \ , \ mathrm {\ cdot} l} {\ mathrm {d}}}}

For a rod earth the formula is:

{\ displaystyle \ mathbb {R} _ {\ text {A}} = {\ frac {\ rho _ {E}} {\ mathrm {2} \ cdot \ pi \ cdot l}} \ cdot \ ln {\ frac {4 \, \ mathrm {\ cdot} l} {\ mathrm {d}}}}

Source:

If several ( ) earth rods are connected in parallel, the expansion resistance is determined using the formula: ${\ displaystyle n}$

{\ displaystyle \ mathbb {R} _ {\ text {A}} = {\ frac {1} {\ mathrm {n}}} \ cdot {\ frac {\ rho _ {E}} {\ mathrm {2} \ cdot \ pi \ cdot D}} \ cdot \ ln {\ frac {4 \, \ mathrm {\ cdot} l} {\ mathrm {d}}} \ cdot {k}}

The constant is depending on the soil moisture ${\ displaystyle k}$

{\ displaystyle k \ approx 1 ... 2}

An earth electrode with the area can be calculated approximately using the formula: ${\ displaystyle A}$

{\ displaystyle \ mathbb {R} _ {\ text {A}} \ approx {\ frac {\ rho _ {E}} {\ mathrm {4}}} \ cdot {\ sqrt {\ frac {\ pi} { \ mathrm {A}}}}}

Source:

For a ring earth electrode with a diameter , the following formula applies approximately: ${\ displaystyle D}$

{\ displaystyle \ mathbb {R} _ {\ text {A}} \ approx {\ frac {\ rho _ {E}} {\ mathrm {2} \ cdot \ pi ^ {2} \ cdot l}} \ cdot {k}}

The constant is: ${\ displaystyle k}$

{\ displaystyle k \ approx 15 ... 20}

The expansion resistance of a plate earth with the edge length is determined according to the formula: ${\ displaystyle a}$

{\ displaystyle \ mathbb {R} _ {\ text {A}} = {\ frac {\ rho _ {E}} {\ mathrm {4}, 5 \ cdot a}}}

Source:

If the plate only comes into contact with a surface with conductive soil, the following formula applies:

{\ displaystyle \ mathbb {R} _ {\ text {A}} = {\ frac {\ rho _ {E}} {\ mathrm {2} \ cdot D}}}

Improvement of the propagation resistance

There are several methods of reducing the expansion resistance:

Use of special filler materials
Use of mineral or chemical bottom electrodes
Use of several earth electrodes connected in parallel

In soils with variable soil moisture, e.g. B. rocky or sandy soils, a special filler is used to improve contact, which is used to improve the contact between the earth electrode and the soil. The earth electrodes are embedded in the filling material and then covered with soil.

To improve the soil conductivity, special soil electrodes are used which are filled with a salt mixture. The ground electrodes have several holes through which the saline solution can migrate into the ground. Filling materials or chemical bottom electrodes are mainly used in lightning protection grounds.

By connecting several earth electrodes in parallel, the contact area with the ground is increased and the resistance to spread is reduced. So that the earth rods do not influence each other, they are laid at a distance of two lengths of earth rod.

So-called chain conductors are connected to further improve the earthing effect, e.g. B. Metal sheaths for cables or earth ropes for overhead lines. In larger structures (industrial plants), the earthing systems are often connected to one another in order to achieve a meshed earthing system. By connecting the individual earthing systems, on the one hand, the potential differences between the earths are reduced and, on the other hand, the earthing resistance of the entire system is reduced.

Earth voltage

With earth electrode , the earth electrode applied to the voltage against the ground potential is referred to. It depends on the expansion resistance as well as the earth current flowing through the earth electrode in the event of a fault :

{\ displaystyle \ mathbb {R} _ {\ text {A}} = {\ frac {\ mathrm {U} _ {\ text {E}}} {\ mathrm {I} _ {\ text {E}}} }}

In house installations, the maximum earth voltage is usually limited by the expansion resistance of the earthing system and the tripping current of the residual current circuit breaker .
If there is no residual current circuit breaker, if the expansion resistance is sufficiently low, the overcurrent protection device , i.e. H. the circuit breaker , switch off. If the protective conductor leading to the earth electrode is interrupted or there is a high expansion resistance, in systems without a residual current circuit breaker, in the event of a fault in the entire building, a very high contact voltage can arise on all metallic components and housings connected to the equipotential bonding.

Larger plants

Earthing of connected buildings must be connected to one another.

Guidelines

DIN VDE 0100-540 Installation of low-voltage systems, Part 5-54: Selection and installation of electrical equipment - earthing systems, protective conductors and protective equipotential bonding conductors
DIN VDE 0101 Power systems with nominal alternating voltages above 1 kV Part 1: General provisions
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
ÖVE / ÖNORM E 8014 - series (construction of earthing systems for electrical systems with nominal voltages up to WS / AC 1000 V and GS / DC 1500 V)

literature

Gerhard Kiefer, Herbert Schmolke: VDE series 106; "DIN VDE 0100 applied correctly, setting up low-voltage systems clearly presented" . 5th edition. VDE Verlag GmbH, Berlin and Offenbach 2012, ISBN 978-3-8007-3384-2 .

Individual evidence

↑ ^a ^b ^c ^d ^e ^f Wilfried Knies , Klaus Schierack: Electrical systems technology; Power plants, networks, switchgear, protective devices .5. Edition, Hanser Fachbuchverlag. 2006 ISBN 978-3-446-40574-5

↑ ^a ^b ^c ^d ^e ^f ^g ^h DEHN + Söhne GmbH + Co.KG .: Blitzplaner. 2nd updated edition, Neumarkt 2007. ISBN 978-3-00-021115-7

^ Georg Flegel, Karl Birnstiel, Wolfgang Nerreter: Electrical engineering for mechanical engineering and mechatronics . Carl Hanser Verlag, Munich 2009, ISBN 978-3-446-41906-3 .

↑ International Electrotechnical Dictionary - IEV 826-13-05

↑ 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 .

↑ ^a ^b ^c ^d ^e ^f ^g ^h Hans-Günter Boy, Uwe Dunkhase: The master's examination in electrical installation technology. 12th edition, Vogel Buchverlag, Oldenburg and Würzburg, 2007, ISBN 978-3-8343-3079-6

↑ Österreichischer Verband für Elektrotechnik, Österreichisches Normungsinstitut (Ed.): Construction of electrical systems with nominal voltages of up to 1000 V ~ and 1500 V -. Part 1: Terms and protection against electric shock (protective measures). (ÖVE / ÖNORM E 8001-1).

↑ ^a ^b ^c ^d ^e Gerhard Kiefer : VDE 0100 and the practice. 1st edition, VDE-Verlag GmbH, Berlin and Offenbach, 1984, ISBN 3-8007-1359-4 .

↑ ^a ^b ^c ^d Klaus Heuck , Klaus-Dieter Dettmann , Detlef Schulz : Electrical energy supply. 7th edition, Friedrich Vieweg & Sohn Verlag, Wiesbaden, 2007, ISBN 978-3-8348-0217-0 .

↑ Reyer Venhuizen: Earthing and electromagnetic compatibility, earthing with a system, Deutsches Kupferinstitut DKI, Leonardo Power Quality Initiative Online ( 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 August 29, 2012). @1@ 2

↑ Diploma thesis Anton Grabbauer: A contribution to the computational determination of grounding impedances. Online (accessed August 29, 2012; PDF; 1.7 MB).

↑ Diploma thesis Johann Frei: Measurement of the impedance of extensive earth systems online (accessed on August 29, 2012; PDF; 2.9 MB).

↑ ^a ^b ^c Winfried Hooppmann : The intended electrical installation practice. 3rd edition, Richard Pflaum Verlag GmbH & Co. KG, Munich, 2007, ISBN 3-7905-0885-3 .

↑ ^a ^b ^c ^d ^e ^f Manual - Examples for standard-compliant planning and installation, Part 1 - Foundation grounding ( Memento of the original from December 4, 2016 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. , 2006 edition, Arthur Flury AG, Switzerland; accessed in December 2016 @1@ 2

↑ Réne Flosdorff, Günther Hilgarth: Electrical Distribution. 4th edition, Verlag BG Teubner, 1982, ISBN 3-519-36411-5 .

^ Paul Waldner: Fundamentals of electrotechnical and electronic building equipment . Werner-Verlag 1998, ISBN 978-3-8041-3983-1 .

^ Andreas Steimel: Electric traction vehicles and their energy supply. 2nd edition, Oldenbourg Industrieverlag GmbH, Munich 2006, ISBN 978-3-8356-3090-1 .

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^ Friedrich Kießling, Peter Nefzger, Ulf Kaintzyk: Overhead lines. 5th edition, Springer-Verlag, Berlin Heidelberg New York 2001, ISBN 3-540-42255-2 .

↑ ^a ^b ^c Hennig Gremmel, Gerald Kopatsch: switchgear book (ABB). 11th edition. Cornelsen, Berlin 2008, ISBN 978-3-589-24102-6 .

↑ Company publication from Dehn: "Corrosion damage to earthing systems"; Special print from Elektropraktiker , Berlin, volume 64 (2010), issue 9, page 3

↑ Swiss Association of Road and Transport Experts : Earthing Manual . Railway technology regulations, Bern 2008.

↑ Wv Baeckmann, W. Schwenk: Handbook of cathodic corrosion protection. 4th completely revised edition, WILEY-VCH GmbH, Weinheim 1999, ISBN 3-527-29586-0 .

↑ Ulrich Bette, Wolfgang Vesper: Pocket book for cathodic corrosion protection. 7th edition, Vulkan-Verlag GmbH, Essen 2005, ISBN 3-8027-2932-3 .

^ Günter Springer : Electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9 .

↑ ENRICO: EARTHING & GROUND CONNECTIONS ( Memento of February 5, 2015 in the Internet Archive ) (accessed on January 18, 2016; PDF; 985 kB).

↑ Franz Pigler : EMC and lightning protection of process control plants . Siemens Aktiengesellschaft, Publicis Corporate Publishing 2001, ISBN 978-3-8009-1565-1 .

↑ Dietrich Oeding , Bernd R. Oswald : Electrical power plants and networks . Springer Verlag Berlin-Heidelberg-New York, Berlin 2011, ISBN 978-3-642-19245-6 .

[Quelle_3-1] ↑ ^a ^b ^c ^d ^e ^f Wilfried Knies , Klaus Schierack: Electrical systems technology; Power plants, networks, switchgear, protective devices .5. Edition, Hanser Fachbuchverlag. 2006 ISBN 978-3-446-40574-5

[Quelle_1-2] ↑ ^a ^b ^c ^d ^e ^f ^g ^h DEHN + Söhne GmbH + Co.KG .: Blitzplaner. 2nd updated edition, Neumarkt 2007. ISBN 978-3-00-021115-7

[Quelle_19-3] Georg Flegel, Karl Birnstiel, Wolfgang Nerreter: Electrical engineering for mechanical engineering and mechatronics . Carl Hanser Verlag, Munich 2009, ISBN 978-3-446-41906-3 .

[Quelle_18-4] International Electrotechnical Dictionary - IEV 826-13-05