The earth electrode is an electrically conductive connection to the electrical potential of the ground. Grounding is a form of ground connection. A ground potential is not the same as the ground potential in general. Through a ground connection ( grounding ) a conductive connection to the conductive environment is maintained. If this environment includes the ground or is conductively connected with it, there is a ground.
To ground is referred to a the ground, and on the other hand, the electric potential of the conductive soil. It consists of earth electrodes for personal protection, protective conductors, earth wire terminals or lightning rods. The area which is outside the effective range of an earth electrode is referred to as a ground reference or neutral earth. Contact between the ground and a randomly selected ground point no noticeable induced by ground voltages on these selected ground point is in the region of the neutral ground.
The ground has to make the goal of a defined reference potential or a potential compensation by which a voltage which may occur will be short-circuited. However, since the ground as any other electrically conductive connection having a resistance, the so-called ground resistance, a voltage is maintained, in the case of a continuous flow of current according to Ohm's law. May therefore be expected in only static applications, that any potential difference with the ground is not possible.
The basic terms for grounding systems in the context of low-voltage systems are described in DIN VDE 0100-200:2006-06 " Erection of low voltage installations " in the main section 826-13 - "Grounding and Connections" set. This standard contains largely the German translation of the IEC 60050-826:2004 with minor national adjustments. The definitions can also use the freely accessible portal ELECTROPEDIA in the "Section 826-13 " queried in 12 languages (or in any of the languages offered for translation ) are.
Types of grounding
Depending on the task and structure, a distinction in electrical engineering four different types of grounding:
- Protective earthing
- Lightning protection grounding
- Functional ground
- Signal ground
With the protective earthing a secure connection is created to the ground to protect in electrical plant and equipment when an error occurs people and animals from dangerous high contact voltages. The protective grounding can also serve the function of grounding, but not vice versa.
The lightning protection grounding should certainly dissipate the lightning current into the ground to protect the building.
The function ground is used to operate electrical equipment safely. With the functional ground noise currents are safely discharged and electrical noise interference can be avoided.
The Signal ground is mainly used in power plants and substations and to ensure trouble-free operation of the plant or equipment.
In many cases, grounds are well combined and meshed with each other.
Tasks of the grounding system
The grounding system (ground) includes all measures that are required to connect an electrical part with the earth and is an essential component in both low- and in high-voltage networks. In new buildings, the earthing system is the first technical device which must be installed. The grounding system consists of the ground wires and one or more earth electrodes. The respective earth electrodes, depending on the installation depth, divided into ground rods that are driven vertically into the ground and surface earth that are laid horizontally. This foundation earth are a special form of Oberflächenerders. They are installed in the foundation below the moisture insulation.
Responsibility of the individual earthing system is:
- Protection of living beings by limiting touch voltage and step voltage
- Lightning protection of installations and buildings
- Intended function of the power supply
- Limit electromagnetic interference
According to these requirements, the respective grounding systems are designed and installed. Certain requirements must be met when designing the grounding system:
- Personal safety
- Corrosion resistance
- Mechanical strength
- Mastery of the highest fault current and its thermal effects
During the installation of earthing system, the designer must take into account both the nature of the soil and the amount of the expected fault currents.
Humans and other animals are at risk if they touch two electrically conductive objects between which there is a dangerously high voltage. Therefore all non- operatively energized conductive parts of electrical loads are connected ( eg body parts) on the so-called protective conductor to the ground potential in high - and low-voltage networks. With this grounding method is the safety ground. The connection of an external conductor with these objects then leads to ground faults, which can lead to tripping of the overcurrent protection device and thus for switching off the voltage.
Grounds for explosion protection measures are similar for ESD protection and protect persons and property. When filling eg tankers, trucks, wagons, barrels, big bags (English for big bag or bulk containers) etc. generate electrostatic charges. With earthing devices to avoid sources of ignition due to electrostatic charge. Grounding devices are, for example, grounding clamps, which clamped to the to be grounded object ( in this case, make sure that for example in a barrel, the "teeth" of the clip really come down to the metal through the paint ) and connected by a cable to an earth electrode be. This thus prevents the formation of sparks and an explosion occurs in an explosive atmosphere.
The so-called Earth rod is an accessory of a mobile generating set. If the generator can not be connected to an existing on-site earth electrode, it is up to one meter long copper rod driven into the ground and connected to the generator system. Modern generator systems usually require no earthing spike, if they are operated as an IT system with insulation monitoring.
Maintenance / Safety
It is mandatory to ground on electrical installations with dangerous voltages, for example, at distribution boards, Overhead lines or overhead wires, switch off the voltage and all electrical conductors from work. The grounding effect in the case of accidental switching a short circuit which leads to the triggering of the fuse, and thus to switch off the voltage. Also, if a remaining charge of the plant can be removed via the ground, for example when working on high voltage lines.
Only in exceptional cases and only for specially trained electricians it is permissible not to do so, for example when working under stress.
The lightning protection is designed to protect people and property.
Lightning protection systems reduce the risk of damage due to lightning strikes in buildings. They consist of air-termination systems, derivatives, grounding and lightning protection potential equalization. Fishing facilities are located at all points that can be struck by lightning. Of them, the derivatives direct the lightning current to the grounding system. Surge protection devices provide when lightning strikes for conducted overvoltages (surge) equipotential bonding of all electrical conductor to the grounded conductor ago. Such conducted overvoltages can be caused by induction of high field gradient or by magnetic coupling of lightning currents on supply lines and signal lines despite lightning protection.
Under the railway world, the grounded rails of railways are understood to be used in single-pole overhead line as a return line. This conventional construction is cost caused by the large distance between the lines, but a wide area field, and is therefore under the terms of electromagnetic compatibility unfavorable. Due to the different local conditions and soil conditions in Europe there are different grounding concepts. The newer name for the train ground connection is to the return line.
There are different grounding concepts for DC and AC railways. The return line systems of direct current paths must be isolated from other grounded parts. In order to improve the return line ratios, ground wires are often laid in parallel as an additional return line to the railroad track.
To prevent electrostatic discharge ( electrostatic discharge - short ESD) grounding straps, table mats and tools are used with dissipative handles for personal grounding and potential compensation. This is always required when electronics or electronic components are handled or installed. In particular, diode lasers, field effect transistors, as well as 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 PCBs or corresponding modules are affected.
The conductive connections between the person, the equipment and the earth reduces voltage differences that could be dangerous to the components. The ESD sensitivity of electronic components is tested using the human body model and specified in ESD sensitivity classes.
See also: Anti -static wrist strap
High -voltage direct current transmission system
In some monopolar systems for high-voltage direct current transmission is, as available, the highly conductive seawater used as the second pole. On land extensive grounding electrodes are required. Grounding is functionally important, but must also take into account aspects of personal safety. A grounding by connecting to grounding pole with objects of the converter station is ruled out for reasons of electrical corrosion and unwanted influence of electrical systems, for example, by biasing of transformers and by stray DC currents. Therefore, the grounding of equipment for high-voltage direct -current transmission is carried out in a suitable place - as available in the sea - in most cases a few kilometers distance from the converter station.
If the ground on land, so usually several graphite electrodes are buried for anodes. For a cathode copper ring is placed in the ground. With electrodes in the sea graphite electrodes or titanium grids are used for anodes. For cathode usually a plain copper ring comes on the seabed with a diameter of about 100 m are used. In both shore grounding systems like those of the Pacific DC Intertie in place Celilo to the earth electrode is located at a distance of 10 km to the converter station in the form of a metallic iron ring with a diameter of more than 3 km in the ground. To avoid electrolysis, which would destroy the metal grounding electrode, the metallic iron ring embedded in petroleum coke, which makes electrical contact with the surrounding soil.
The location of these electrodes must be carefully chosen in relation to the possible danger of corrosion, others in the bottom of metal parts, such as pipes or the influence of electrical systems. It should not be too close to the cable route in high voltage direct current transmission systems with submarine cables, as this can drain leakage currents over the cable sheath, which can cause it to corrode.
Antennas require especially at long wavelengths to be transmitted or received, the radio waves a ground to improve their function. Continue to exposed to or mounted on a roof antennas are grounded to provide lightning protection. This protects people and connected equipment against damage. Especially elaborate grounding systems can be found in transmitters for long wave, medium wave and long wave, because in such systems, the efficiency depends critically on the low impedance of the grounding from. For transmitter systems for long wave, medium wave and long wave several metal strips are buried at the antenna site at shallow depths (10 to 50 centimeters), the run away radially from the antenna center. Does the soil, no burial, so they are possibly installed above ground on small masts. In this case one speaks of the counterweight. Erdbänder this should be at least as long as the antenna carrier is high. In most cases, a value of a quarter of the wavelength emitted is sufficient, but there have been Erdbänder with a length of 1.5 times the wavelength of the emitted laid. We call such a system as a ground network. If the antenna support on a platform in the sea, so can be dispensed with a ground network because of the good conductivity of seawater. This also applies in the long run, long and medium wave transmitter on board ships. For VLF transmitter with particularly low frequencies, such as the Sanguine and ZEVS over a ground rod grounding Bodendipol used. In these systems, the earth electrode are submerged in several meters depth.
The functional grounding of audio amplifiers or signal sources is used to avoid over electrical noise interference received by their metal housings are connected together and to the ground. Oscilloscopes and other devices like computers often have an electrical connection to the signal ground to the protective conductor of the mains power connector to reduce noise interference or noise radiation. Housing and signal ground other devices are often connected to this end also only about an RC circuit to the protective conductor.
Connections for the functional ground or earth connection must not be marked as protective earth compounds and must not be used as a protective earth connection.
Problems by grounding
Due to the variety of different earthing systems may occur affecting the earthing systems with each other. This is particularly noticeable in urban areas with dense development noticeable when railway lines run close to the buildings. Through Potential differences may be overlap of the traction current to the three-phase system. This means that systems no longer function properly. In the worst case, these overlays can cause damage to the ground, or even destroy, the PEN conductor. By stray DC currents occur near DC railways to strong corrosion on earth electrodes made of galvanized steel.
Via the ground into the ground initiated alternating currents for prolonged time to corrosion of pipelines. This has a particularly out if pipes are used as an earth electrode.
The presence of a terminal to a Potentialerder itself does not guarantee its suitability and safe grounding. Therefore, after setting up a Potentialerders a check for dissipation of fault currents according to VDE 0100, etc. must be done.
- DIN 18014: Foundation Earth - General planning principles.
- DIN VDE 0100-200: Erection of low- voltage systems - Part 200: Definitions.
- DIN VDE 0100-410: Erection of low- voltage equipment - Part 4-41: Protection for safety - Protection against electric shock.
- DIN VDE 0100-444: Erection of low -voltage electrical installations - Part 4-444: Protection for safety - Protection against voltage disturbances and electromagnetic disturbances.
- DIN VDE 0100-540: Erection of low- voltage electrical installations - Part 5-54: Selection and erection of electrical equipment - Earthing arrangements, protective conductors and protective bonding conductors.
- DIN VDE 0141: Earthing system for special power installations with nominal voltages above 1 kV.
- DIN VDE 0151: Materials and minimum dimensions of earth electrodes with respect to the corrosion.
- DIN VDE 0185-305-3: Protection against lightning - Part 3: Physical damage to structures and people.
- DIN VDE 800-2-310: application of measures for equipotential bonding and earthing in buildings with information technology equipment.