Electric power transmission

In principle, a power grid is a broad term and referred to in the electric power industry, a network of electric power lines as underground cables and overhead lines and its associated equipment, such as switchgear, substations and the connected power plants and consumers.

• 5.1 Transmission System Operators ( TSOs) 5.1.1 Germany
• 5.1.2 Switzerland
• 5.1.3 Austria
• 5.1.4 European cooperation

Term

There are various and common names for the mains: power grid, light grid, power grid, power system, power system, power supply system, electricity grid and power grid. In automobiles and airplanes is called from the vehicle.

In Germany the term mains usually stands for the grid to supply the consumer by the energy supply companies with electrical energy.

Tasks

Power grids are used to supply consumers with electricity and provide the link with the electricity-generating power plants forth at different voltage levels. In the transmission of high power high losses may occur, which can be reduced by high voltages. This considerably reduces the required cross section of the power lines and the cost of switching devices. The power supply system typically includes four voltage levels. The overall high voltage grid is designed in Europe in general to 400,000 volts ( corresponding to 400 kV ) and 230,000 volts ( 230 kV). In the high- voltage network 110 kV are common. In the downstream medium voltage grid voltage steps 1 to 30 kV are common. The low voltage level among consumers is operating at 400 volts for three-phase alternating current and 230 volts for single phase. When mains frequency is customary in Europe 50 hertz ( Hz).

In other countries and continents other voltage levels or frequencies in power systems have developed. A higher voltage is used for example in Poland at the 750 - kV line Rzeszów -Khmelnytskyi. In the high voltage range Ekibastus - Kokshetau be used with 1.15 MV for example in Asia on the three-phase line. In North America, the single-phase three-wire system with 120 V and 240 V mains voltage and mains frequency of 60 Hz is common in the low voltage range.

A special feature in Germany represents the current network of Deutsche Bahn, which is operated with single-phase at a frequency of 16.7 Hz. In the early days of electric drives for locomotives beginning of the 20th century, the sparking at the rotary joint ( commutator ) could only be limited by the fact that the operation at low frequency was. Therefore Maschinenumformer or generators have been used by the pole pitch of the grid frequency was divided into three portions of 50 Hz, yielded 16 ⅔ Hz as the frequency of the current track.

Overhead line networks for the distribution of electric energy are also used for communication, by means of carrier frequency method on the conductor cables, on the ground wires or mitverlegte news cable (usually fiber optic cables ) The message transmission is used by the energy suppliers themselves or offered to other users.

Technology

Voltage levels

Power grids dividing one by the voltage at which they transmit electrical energy:

• High Voltage: In Western Europe, usually 230 kV or 400 kV. 735 kV and 765 kV are used in Canada and the United States. In Russia there is an extensive 750 - kV network, leading from the individual lines to Poland, Hungary, Romania and Bulgaria. A 1150 -kV line leads from the power plant Ekibastus (Kazakhstan ) to the city Elektrostal (Russia). It is now, however, operated at 400 kV.
• High voltage: 60 kV to 150 kV. In Germany and Austria almost always 110 kV is used. Besides that, there in Schleswig -Holstein, in Winsen ( Aller), near country mountains, in the Saarland and at Phillipsthal lines with 60 kV operating voltage.

In Switzerland, no uniform value exists in the high -voltage grid.

• Medium voltage: 1 kV to 30 kV. For networks with a high proportion of overhead line, vast rural areas and in new installations 20 kV to 25 kV are common. In urban areas, where some even older underground cables are used in paper -lead design with aluminum as a current conductor whose replacement is expensive, a lower medium voltage with 10 kV is applied.
• Low-voltage networks: 230 V or 400 V. In the industry are also other low- voltage common, for example, 500 V or 690 V.

The high, high and low voltages are largely standardized for Western Europe. Medium voltage that is too expensive, because you would have to replace a lot of old underground cable inconsistent maximum operating voltage.

Function of the individual networks

• The transmission system uses the three-phase high voltage transmission ( Dhu, Eng. HVAC). It distributes the heat generated by power plants and fed into the grid energy nationwide on power transformers, which are close to the load centers. It is also connected through so-called feeder lines to the international network system.

• The Europe usually operated at 110 kV distribution network ensures the coarse distribution of electrical energy. Lines lead here in different regions, urban centers whose substations or large industries. Covering a power requirement of 10 to 100 MW.

• The medium-voltage network that distributes the electrical energy to the regionally distributed transformer stations or major facilities such as hospitals or factories. Public utilities, which are also smaller power plants often operate with combined heat and power, feed their electricity into the medium-voltage network.

• The low-voltage networks are responsible for the dispersion. The low voltage is transformed in Europe to the usual 400 V or 230 V and thus are private households, small industries, commercial and administrative supplies. These lines are referred to as the last mile. Small - about private - photovoltaic systems feed excess power on this one low-voltage level.

The distribution transformers in medium voltage networks have a fixed ratio in general. In order spite of occurring in the course of a day large load fluctuations can keep the mains voltage to the consumer is approximately constant, the ratio of the power transformers between high and medium voltage network may ( eg 110 kV/20 kV ) can be varied within limits. To a plurality of taps are led out from the primary winding. A specially -built switch, called a step switch allows switching between the taps without having to switch off the transformer to do so. This process is called voltage regulation. For the proper function of many devices, power must be maintained within narrow limits. Too high or too low voltages can be caused by disorders.

There are also cables with high-voltage direct current for transmission over long distances, particularly submarine cables in the form of high-voltage direct current (HVDC ).

Connection of the power networks with one another

The connection of power grids with different voltage levels via transformers that are installed in substations. The current flow through the networks and networks with the same voltage level is via switchgear. Grids with different phase number or frequency or power networks, are not synchronized with each other, must be interconnected via HVDC or Motor-/Generator-Kombinationen.

Grid system

In a composite network, several power plants and customers centers are summarized and the difference between local supply and demand of instantaneous power can be better balanced within the network. They thus represent the opposite pole to island networks dar.

Through an integrated network offers advantages:

• The energy system will be more stable, as this excess capacity and lower capacity can be intercepted or be compensated,
• Through power exchange load fluctuations can be better compensated than just the short term by controlling the power plants, and
• The reliability of the network is increased.

Within a composite system, all producers must operate synchronously. Three -phase alternating current leads to increased transmission loss in the wires, so it is not used for example, for a submarine cable of more than 30 km in length. In Central and Western Europe is operated on the territory of the Union for the Co -ordination of Transmission of Electricity ( UCTE), a European network system, the organizational interests were taken over by the ENTSO -E in 2009.

Supply network

A supply network is designed for recording and transmission of electricity from renewable energy sources be blank power supply, which is often connected to the supply network with the transmission system. Einspeisenetze are a fundamental component of hybrid power plants. In contrast to public water networks Einspeisenetze are less redundant and less hours at full load and thus to build quickly and cheaply ( as a regional underground cable networks). Einspeisenetze serve in particular to improve the system integration of renewable energies in the electricity sector .. An example is the supply system of Enertrag in Uckermark

Distribution

The electrical energy can in these quantities over power lines wired only - to be transferred - overhead lines and underground cables. Both systems have advantages and disadvantages.

Speak the lower cost and easier localization and reversibility of errors for the use of overhead lines. Overhead lines are exposed to environmental influences (eg storms ), the landscape can affect and can, in rare cases, people, animals and property at risk.

There are different types of overhead line masts. Specific problems in the pipeline at the crossing of obstacles see overhead line crossings.

Underground cables have a smaller footprint, are better protected against environmental influences and accepted by the public. Its construction is significantly more expensive; the maintenance in case of defects is high and there are technical problems that when underground power lines exceed certain cable lengths. For example, the heat dissipation overhead lines by the surrounding air is guaranteed, with underground cables not. Further problems arise because of the enormous reactive power, which in turn is due to the high capacity of the cable.

The German electricity grid is about 1.78 million km long:

In 2003, about 71 % were buried. A comparison to the value for 1993 - about 64 % - shows the trend, according to the line expansion in the field of low-voltage networks and partially medium voltage, expand the underground power distribution. In the Building and in particular maximum voltage range which laid underground underground cable systems do not play a role with respect to length proportion.

Network topologies

Electricity networks are set up differently in their structure. The topology is based on various evaluation Criteria such as voltage level, spatial boundary conditions, operating costs, or security of supply. The main network types are:

Radial network

The power is supplied from a central feed point from which individual lines, referred to as a stub line running radially to the individual points of consumption. In this topology, low-voltage systems are often designed. The advantage is low planning, easy troubleshooting and low demands on the network protection. The disadvantage is a low security of supply, since all loads connected to it suffer a power failure upon failure of a spur line.

Ring network

Ring networks are fed from one or more locations, the supply of the individual consumer takes the form of a loop: A consumer can therefore be powered from two sides over the ring. In a technical defect of the ring can be opened to the fault location around which the consumer may be off the fault still supplied. The advantage is the higher qualification of maintenance personnel since the unlock of a network section in the ring due to the actuation of multiple switching points increased security of supply, the disadvantage. A special form, with increased reliability, represent double ring network, in which two ring networks are performed spatially parallel: Each consumer can then optionally be powered by one of the two ring networks. Find application ring networks with larger low-voltage networks, particularly in urban areas, in medium voltage networks and on the 110 -kV distribution network level where usually double ring lines provide more child substations.

Mesh

Mesh networks are generalized ring networks represent, are usually fed at several points and consumers are distributed in a network that has multiple nodes and branches. The power consumption of individual points is usually carried out over two or more lines, the concrete form depends primarily on the performance requirements and spatial conditions. A mesh network provides an appropriate design, the maximum security of supply, but will require a massive complex network protection. Also need methods to control the individual power flows on individual branches, the connecting lines within the network exist, because each line has only a limited transport capacity. Find application mesh networks among others in the transmission networks with high and very high voltage, such as the 380 kV level. Interconnections are usually a combination of several spatial mesh networks.

Network conditions

In the context of network operations, a distinction between different network states, which provide information about whether the supply network of its task for electrical energy distribution can meet. In the rules on network operation of transmission networks distinguishes between four different network conditions, which are in case of disturbances through from top to bottom:

Network operators

Transmission system operators ( TSOs)

In the field of high voltage networks, the networks of the individual TSOs are interconnected via high voltage lines to the national grid.

Germany

In Germany four network operators ( TSO Transmission System Operator ) operate; they have teamed up with the German system control network: Amprion, EnBW, TenneT TSO and 50 Hertz Transmission.

Switzerland

The Swiss electricity grid is of great importance for the Western European electricity trading; It is used traditionally as a hub for the compensation of peak demand and peak production of large continental European countries. The power in the narrow sense was spun off in 2009 from the individual power companies (EVU) in so-called grid companies and has been in the national transmission system operator (TSO ) Swiss Grid transferred.

Austria

In Austria, the national transmission network of the Austrian Power Grid (APG ) is operated.

European cooperation

The European Transmission System Operators, who are responsible for the operation of the high voltage electricity grid, have formed a federation called ENTSO- E 2007; before that there were six old associations ( " ETSO "). They were responding to the third internal energy market package of the European Commission; this was adopted in 2009. ENTSO -E also represents the network operator to the Commission.

Distribution system operators ( DSOs )

In addition to the transmission system operators, there are a number distribution. In Germany there are about 900 small distribution system operators, supply electricity to end users.

The network operators network usage charges for the service " passing current from the power producer to consumer ." Prices for this service is in Germany laid the Federal Network Agency.

Power grids of the railways

Another power grid in Germany, Switzerland and Austria operates the train. DB Energie operates the largest interconnected 110 kV grid in Germany. It usually consists of four conductors, while other 110 kV grids usually consists of three or six conductors. The overhead line network has a length of about 7600 km of railway power lines. In traction power network other than the national interconnected grid is the grid frequency of 16.7 Hz and it is single phase used.

Besides that, there small regional power grids as the operated with single-phase and a frequency of 25 Hz Mariazellerbahn in Austria. This path has a small private 27- kV network.

In the other countries the power supply for electric railways from the public power grid is done. In direct current paths through rectifier substations, operated with single-phase at a frequency of 50 Hz tracks the phases of the three-phase system can be broken down in the sub-station and assigned to different sections.