How is the grounding done in ships




The Grounding is an electrically conductive connection with the ground. It consists of earth electrodes, connecting cables and corresponding terminals.

Grounding is a form of grounding. A grounding creates a conductive connection with the conductive environment. If this environment includes the ground or is conductively connected to it, there is an earth connection.

Like grounding, earthing often has the aim of establishing a defined reference potential or equipotential bonding by means of which a potential voltage is to be short-circuited. However, since the grounding, like any other electrically conductive connection, has a resistance, the so-called grounding 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.

Earth electrode

An earth electrode is an uninsulated electrical conductor that is inserted into the ground as an electrical contact surface.

One distinguishes

  • Earth rods that are driven vertically into the ground
  • Surface earths that are laid horizontally
  • Foundation earth as a special form of surface earth

Due to the moisture in the ground, earth electrodes are at risk of being destroyed by corrosion or by the formation of a galvanic element with other metal parts. This must be taken into account when choosing the material.

In the past, the pipeline networks of the public water supply were used as an earth electrode. Because plastic pipes are now used there instead of metal pipes, this is no longer permitted.

Deep earth rod

Deep earth rods are designed as rod earth rods, tubular earth rods or cross-shaped earth rods. They are driven up to 15 m underground. The advantage of a deep earth electrode compared to a surface earth electrode is the more constant earth resistance, which can vary greatly in the vicinity of the surface depending on the humidity and temperature of the soil.

Surface earth

Surface earths are horizontal earths. They run as

  • Ring earth electrodes that form a horizontal ring
  • Radiant earth electrodes that diverge horizontally
  • Mesh electrodes that form a grid

They are laid at a depth of 0.5 - 1 m so that they are in a frost-free zone.

see also: potential control

Foundation earth electrode

Foundation earth electrodes are a special form of surface earth electrode. They are laid in the foundation below the moisture insulation.

Applications

A basic distinction is made between protective earths, which are used for electrical safety, and functional earths, which are used for other purposes.

Protective earthing in the low-voltage network

People and other living beings are at risk if they touch two electrically conductive objects between which there is a dangerously high electrical voltage. As long as only one of the conductive objects is touched, there is no danger. In the low-voltage network for supplying power to consumers, one of the conductors, the so-called protective conductor, is therefore earthed and connected to electrically conductive objects. The connection of another conductor to these objects then leads to a short circuit, which triggers the overcurrent protection device and thus switches off the voltage.

Overcurrent protection devices are designed for line and device protection and do not switch off quickly enough to protect a person who touches an earthed object when such a fault occurs. This is why residual current circuit breakers, which switch off the voltage quickly enough even with small currents flowing through the earthing system, make sense and are prescribed for swimming pools and construction sites, for example.

Protective conductors must be marked with green-yellow insulation. Green and yellow marked conductors may only be used as protective, equipotential bonding or earthing conductors. If the outer conductors of electrical lines have a cross-section of more than 6 mm², the protective conductor must not carry any current during normal operation. As a rule, such lines must therefore have an additional neutral conductor.

It used to be common in some regions not to lead separate protective conductors and neutral conductors to sockets, but rather to connect the earthed conductor to the protective contact and one of the other two contacts. If this only earthed conductor of the supply line, which is then loaded with electricity during normal operation, is interrupted, the full mains voltage is applied to objects that should actually be earthed. This is why this so-called classic zeroing (TN-C system) has no longer been permitted in Germany since 1973.

TN systems

In TN systems (French. Terre Neutre) a grounded protective conductor is carried by the distribution network operator. Only with a real TN-S system (French. Terre Neutre Separé) separate neutral conductors (N) and protective conductors (PE) are routed from the transformer to the consumables, while a TN-C system (French. Terre Neutre Combiné) uses a common PEN conductor that is both a protective conductor and a neutral conductor. A TN-C-S system (French. Terre Neutre Combiné Separé) is initially constructed like a TN-C system from the transformer, but the PEN conductor is then, usually in the meter cabinet, divided between a neutral conductor and a protective conductor. In Germany, the TN-C system still predominates in old buildings, while newer installations (except in Thuringia) use TN-S or TN-CS networks.

TT system

In TT systems (French. Terre Terre) no earthed protective conductor is carried, so that the earthing at the house connection is of decisive importance. The advantage of the TT system is its greater reliability on long unsupervised overland routes where the neutral conductor can be damaged or stolen. TT networks are z. B. common in agriculture. In the state of Thuringia, they are also used in urban agglomerations.

IT system

The IT system (French. Isolé Terré) is the earth insulation, which at the same time takes into account increased requirements for personal protection and reliability in the event of insulation faults. IT systems are used, for example, in medical technology, in operating theaters, intensive care units and in medium-voltage networks for the internal use of power plants. They are only suitable for relatively small networks.

Mobile power generating sets

The so-called earthing spike is an accessory part of the mobile power generation unit from the fire brigade or THW. 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. More modern generators usually no longer need an earthing spike if they are operated as an IT system with an insulation monitor.

 

Osh

Before working on electrical systems with dangerous voltages, e.g. distributors, it is mandatory to switch off the voltage and to earth all electrical conductors. It is only permitted in exceptional cases and only for qualified electricians to refrain from doing this, for example when working under voltage. In the event of unintentional switching on, the grounding causes a short circuit that triggers the fuse and thus switches off the voltage. In addition, any charge that may still be present in the system can be discharged via the earthing system, for example when working on high-voltage lines.

Lightning protection

Lightning protection systems reduce the risk of damage from lightning strikes in buildings. 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 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 grounded protective conductor for conducted overvoltages (surge).

Protection of electronic components

To prevent ESD (electrostatic discharge - Electrostatic discharges) are used for earthing people and for equipotential bonding, earthing straps, table mats and tools with dissipative handles. This is always necessary when electronics or electronic components are handled or assembled. 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 the corresponding assemblies are touched.
The conductive connections between the person, the device and the earth break down voltage differences that could be dangerous to the components. The ESD sensitivity of electronic components is determined by the human body-Model tested and specified in ESD sensitivity classes.

see also:Anti-static tape

Railway earth

Railway earth refers to the earthed running rails of railways that are used as a return line for single-pole overhead lines. This usual 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.
Trams and subways use direct current. The voltage drop along the rails causes constant fields in the ground which, due to electrolytic corrosion, lead to major damage to metallic pipelines, among other things. To reduce these potential differences, the polarity of the overhead contact line is changed from section to section. For this purpose, there are insulating spacers in the overhead line between these sections, which must be passed through without electricity to avoid arcing.

DC transmission

In some monopolar systems for high-voltage direct current transmission, the highly conductive seawater is used as the second pole. Special grounding electrodes are required for this. 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 the premagnetization of transformers by stray direct currents. This is why systems for high-voltage direct current transmission are earthed at a suitable location - often 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 meters is usually used for cathodes.

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 transmission

Very complex earthing systems can be found in transmission systems for long wave, medium wave and long wave and in monopolar high-voltage direct current transmission systems, because the efficiency of such systems depends crucially on the low resistance of the earthing. 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. If the ground does not allow burying, these may be laid above ground on small masts. In this case one speaks of Counterweight. 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 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 waves with particularly low frequencies, such as the Sanguine and ZEVS, a ground dipole is used that is earthed via a deep earth rod. In these systems, the earth electrodes are sunk several meters into the ground.

Norms

  • DIN 18014: Foundation earth electrode.
  • DIN VDE 0100 Part 410: Setting up high-voltage systems with nominal voltages up to 1000 V, Part 4: Protective measures, Chapter 41: Protection against electric shock.
  • DIN VDE 0100 Part 444: Electrical systems in buildings, protective measures, protection against overvoltages - Protection against electromagnetic interference (EMI) in systems in buildings.
  • DIN VDE 0100-540 Erection of high-voltage systems with nominal voltages up to 1000V - Selection and erection of electrical equipment - Earthing, protective conductor, equipotential bonding conductor.
  • 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 V VDE V 0185-3: 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.

Category: Electrostatics