The 50Hertz power junctions How substations work

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The 50Hertz power junctions

How substations work

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An electric current has to travel a long way before it reach-es the wall plug. Renewable and conventional installa-tions that produce power are spread all over Germany, and are not always located at the centre of consumption. The 50Hertz control area covers the north-eastern part of Ger-many. Forty per cent of all German wind turbines can be found here, as the wind conditions for these installations are most favourable in the north. Nevertheless, this region only accounts for a little under 20 % of the total German

Secure supply of electricity

The basis of modern society

It is impossible to imagine modern society without electricity. Innumerable

elements of our daily lives depend on a permanent supply of electricity. As

current is an uninterrupted flow, it has to be transported from its point of

or-igin to its point of destination, while balance has to be maintained between

generation and consumption at all times.

power consumption. To put the surplus of unconsumed en-ergy to use, it is transported to other users across Germa-ny and Europe by way of the electrical grid. This happens at different voltage levels.

At important points in the electricity grid the transmission lines come together. These are the substations. If transmis-sion lines over land can be considered as “electricity high-ways”, the substations act as the “power junctions” as well as the “exit and entrance ramps”.

The extra high voltage (380 kV), which is the most efficient for the power transmission, is simultaneously transformed into a high voltage (110 kV), which is necessary for the power distribution.

But how does the voltage conversion in the substations work and which different types of substation are there? This brochure offers the answers to these questions.

50Hertz

The secure and reliable supply of electricity, the integration of renewable energy sources and the facilitation of the electric-ity market: these are the core tasks of 50Hertz. With its total length of about 10,000 kilometres, our transmission system is the backbone for the secure supply of electricity to over 18 mil-lion people in north-eastern Germany – 24 hours a day, 7 days a week, 365 days a year.

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Schleswig-Holstein

Hamburg

Energinet.dk

Denmark

Mecklenburg-Western

Pomerania

Brandenburg

Berlin

Saxony

Saxony-Anhalt

Thuringia

Lower Saxony

Hesse

Bavaria

PSE

Poland

Cˇ EPS

Czech Republic

TenneT

Güstrow Gera Leipzig Halle Erfurt Eisenach Rostock Schwerin Dresden Weimar Potsdam Cottbus Chemnitz Zwickau Jena Magdeburg Frankfurt (Oder) Neu-brandenburg

Key

50Hertz Supply network planned / under construction Other companies HVDC link Converter station Conventional power plant (lignite- or coal-fired, or pumped storage plant, wind farm onshore/offshore) planned / under construction switching stations / substations switching stations / substations planned / under construction MSCDN1_installation

planned / under construction Phase shifter

Phase shifter

planned / under construction Gas-insulated switching stations Other companies

1_{MSCDN = Mechanically switched}

capacitors with damping network

Sta

tus as of

August 2

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In order to cover the large distances that separate producer from consumer, the power generated is either directly inject-ed into the high-voltage transmisson grid or transforminject-ed to 220 kilovolts or 380 kilovolts. In this manner, the electrical en-ergy is transported wide and far throughout the German and European transmission system. By way of the extra high-volt-age grid, the power reaches the second level, which in most cases is the distribution system of the regional electricity utili-ties for ciutili-ties and industrial customers. The voltage is reduced to 110 kV. To supply industrial installations, businesses and smaller towns with power farther down the line, it needs to be injected into a medium-voltage distribution grid with a level of 10 kV to 35 kV. The lowest voltage level requires a voltage of 230 volts or 400 volts to supply private households and small-er businesses.

Substations are the links between all four of these levels.

The electrical system

Four levels of

power supply

Large power plants

Renewable energy plants (e. g. onshore and offshore wind farms), large hydroelectric and pumped storage plants, large conventional power plants (coal, gas)

Medium-sized power plants

Medium-sized renewable energy plants, onshore wind farms, large solar plants

Smaller power plants

Smaller renewable energy plants, onshore wind farms, solar parks and roof systems, biomass, smaller hydroelectric and pumped storage plants, small conventional power plants (gas)

Small power plants

Power generation

Small renewable energy plants, onshore wind farms, domestic roof systems, small decen-tralised power plants (e. g. combined heat and power units)

In Germany, four different voltage

levels are used to supply electricity,

whether to large industrial steelworks

or private households.

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50Hertz The 50Hertz power junctions · 5

Large power plants

Low-voltage distribution

system (230–400 V)

Medium-voltage distribution

system (10–35 kV)

High-voltage distribution system

(110 kV)

High-voltage transmission system

(220–380 kV)

Medium-sized power plants

Smaller power plants

Small power plants

Households businesses Commercial companies industrial companies small cities Energy-intensive industry and cities Very energy-intensive industry

Consumers

Substation

Power grid

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Current

An electric current is like a stream: negatively charged elec-trons emit an impulse in a certain direction. Like a water cur-rent, electricity has a flow. In a stream, water flows through a river bed. Similarly, electric current flows through a conduc-tor made of conducive material. Different elements have dif-ferent conducive properties. Metals like aluminium or cop-per are particularly well-suited. The flow of water is an effect of the difference between a river fount and a river mouth. An electric current, however, requires a voltage difference in-stead. Current is measured in ampere.

Voltage

The voltage is the difference in pressure that makes free electrons move. It is the result of a difference in the charg-es at both ends of the conductor. The electrons strive to balance this difference. This causes the movement of elec-trons within the conductor, from the negative to the positive pole. The entire electricity supply is based on this principle. Electric voltage is measured in volts.

Physical principles

Current and voltage

Power transmission at 50Hertz

The electric current flowing through the electricity high-ways of 50Hertz has a voltage of either 220,000 volts or 380,000 volts. This high voltage enables the transport of large volumes of electricity across wide distances in Ger-many and abroad with only a limited loss of energy.

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Alternating current

Alternating current owes its name to one of its important characteristics: it changes direction, this happens 100 times a second. Its frequency is therefore 50 hertz. Through our power grid flows three phase electric power, also called three phase current. The electric current is created by the rotation of an electromagnet inside a generator. This creates a sinu-soidal alternating current. As the electromagnet moves past three coils set at an angle of 120 degrees, each rotation cre-ates three subsequent voltages (phases) with a 120 degree angle. This type of current can be transformed to any voltage level and is therefore suitable for power transmission.

Direct current

Contrary to alternating current, direct current does not change direction. It is used in pretty much every household. To transform alternating current to direct current, electrical devices have their own small transformers, connected to a rectifier. t (time) U (voltage) Waveform of single-phase a lternating current t (time) U (voltage)

Waveform of direct current

Alternating and direct current

120° 120° 120° U1 U2 U3 t (time) U (voltage) Waveform of three-phase alternating current

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On its way from producer to

con-sumer, the electric current passes

through many stations. It does so

at different voltage levels, higher for

long-distance transport and lower

for shorter distances. The change in

voltage, the so-called

“transforma-tion”, takes place in substations via

transformers. That is why they can

be described as “junctions” where

different “streets” meet.

What is a

substation?

At first sight, a substation appears quite large – the instal-lations, which are usually placed outdoors, require a lot of space in an open area – and hopelessly complex. However, significantly smaller installations placed indoors, often in cities, are just as impressive. If you take a closer look at the compo-nents, you will see that there is actually a clear structure. Fur-thermore, a substation needs to be easily accessible, as the transport of a transformer weighing several tonnes requires a good connection to streets, waterways or railways. That is why the installations are often built in the immediate vicinity of the transport infrastructure.

The electric current arrives at the “power junction” from the conductor and flows through a switchgear bay towards a transformer. That is where the actual transformation to an-other voltage level takes place. At the new voltage level, the electric current leaves the substation to a different conduc-tor, which leads it to the next substation or straight to the consumer.

Aside from the devices that play an active role in electricity transmission and voltage transformation (what we call “operat-ing facilities”), the substation also includes a number of build-ings. The most important of these are the operating buildings and relay buildings, which house the equipment for the control and monitoring of the operating facilities.

Switchgear and substation

A switchgear is called a substation if it contains at least one transformer.

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Surface for a secure electricity supply:

the 50Hertz‘s substations can have a surface of up to 240,000 m² – the same as 24 football fields.

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Legend

Line switchgear bay Transformer switchgear bay Coupler bay Example of an electric current

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The electric gear reaches the substation through the inbound

conductor, which leads to the feeder disconnector with earth-ing switch. This is the connection between the conductor and the switchgear. Next is the current and potential transformer. Both functions are combined in a single device and are used for monitoring and protection. The circuit breaker is the central component of a switchgear bay. In normal circumstances and in case of a disturbance, it switches the electrical circuit on and off. The switchgear bay is connected to all busbars via the busbar disconnectors.

The different busbars can be switched by means of a cou-pler bay. This is also connected to the busbars by the bus-bar disconnectors. The busbus-bars are connected to the transformer bays. The transformer is the link between the different voltage levels. At its lower voltage side, there is an-other transformer bay, from where the outbound conductor leads to the next substation.

The current‘s course

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Surge arrester

7

Busbar

8

Lightning conductor mast

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Portal

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Relay and operating buildings

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Transformer

2

Disconnectors

3

Earthing switches

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Current and potential transformer

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Circuit breakers

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system to the distribution system – are about as large as a personal garage. Both on the outside and the inside, they are mainly constructed in metal. A transformer has a prima-ry and a secondaprima-ry side. On the primaprima-ry side, the power on the high voltage side flows through a large coil. This coil is wrapped around a large iron core. The magnetic field that is created inside the transformer induces a current in the coil on the secondary side. As the proportions of the coils are different, the voltage is lowered to 110 kV.

Inside the transformer, oil is used as insulation and a means to dissipate heat. The oil is cooled in large heat exchang-ers next to the transformer, so that the latter can be properly cooled in each operational state.

But how are these 380,000 volts brought down to the voltage used in households? Transformers take care of this change in voltage. The large jump from high voltage (380,000 volts) to household voltage (230 volts) can, however, not be made in a single bound. The grids using these different voltage levels are all connected by substations. The closer these substations are to the final consumer, the lower the voltage and the small-er their size. The transformation to the standard voltage used to connect residential buildings to the grid takes place in the immediate vicinity.

Transformers that adjust voltage levels from 380 kV to 110 kV – meaning from the voltage level of the transmission

The centrepiece of the substation

the transformer

1 The maximum voltage used to

trans-port electric current in the European

transmission system is 380,000 volts

(380 kV) in order to keep the losses

as low as possible.

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The heavyweights of the energy supply:

transformers can weigh several hundred metric tonnes. The transformers mostly used in the 50Hertz grid, for instance, weigh as much as 75 motorcars.

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- Line switchgear bay – this connects the high voltage power line with the busbars;

- Transformer switchgear bay – this switchgear bay con-nects the transformer with the busbars. Noteworthy is that the transformer is connected directly and not by means of a disconnector.

- Coupler bay – this switchgear bay forms a flexible con-nection with the busbars.

The combination of the devices surrounding a circuit breaker – disconnectors and earthing switches and combined instru-ment transformers that form a functional unit with the circuit breaker – is called the switchgear bay. At the centre of each switchgear bay is the circuit breaker, which can interrupt the current both in normal operating conditions and in case of disturbances. The switchgear bay is connected to the oth-er opoth-erating facilities via disconnectors with an integrated earthing switch. The combined instrument transformer re-ports information on the current and voltage to the protec-tion and control systems. According to the funcprotec-tion, a dis-tinction is made between:

The elements

of the substation

Each operating facility inside a substation fulfils an important function,

var-ying in shape and size depending on its location and purpose. They ensure

that the total installation can be operated securely and reliably.

How is an underground cable connected?

When power is supplied to the substation via a high-voltage underground cable instead of an overhead line, the overhead line portal is replaced by the cable portal. In addition, specific facilities also need to be installed to operate the cable. These are compensation reac-tors which regulate the reactive power needed by the cable, as well as surge arresters.

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Earthing switches

An earthing switch provides a safe and reliable ground connection for a deactivated and therefore voltage-free system component. It prevents the danger occurred through the charge processes. In combination with the disconnectors, they create a safe working environment inside the substation.

Disconnectors

Disconnectors can be found almost everywhere in a substa-tion. Depending on the location, these are feeder or busbar disconnectors. Their purpose is to open the electrical circuit and to completely isolate certain system components from the rest of the installation. They do not connect or nect the current. Within your own home, opening a discon-nector can be as simple as unplugging a switched-off appli-ance or device.

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Circuit breakers

The circuit breaker is the high-voltage equivalent of a light switch and a miniature circuit breaker. It activates and de-activates lines and system components, irrespective of whether there is a normal load current or a disturbance. Aside from the transformer, this is the most important high-voltage device of the substation.

5 Current and potential transformers

For the secure operation of a substation, it is necessary to know of the state of the grid system at all times. The data needed to determine this state are supplied by current and potential transformers. Additionally, these data are processed by the protection and control sys-tems, so that they can respond automatically in case of disturbances.

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Surge arrester

Surge arresters can often be found at the end of an over-head line or a cable. They limit over-voltages or surges, which are brief voltages that are significantly higher than the normal voltage and can be caused, for example, by a lightning stroke. By limiting the voltage to a normal level, the devices in the substation can be protected without in-terrupting the supply.

Busbar

The busbar is the backbone of the substation. Tubes con-nect the different switchgear bays and take care of power transmission within the substation. In order to increase the failsafe performance and more flexibly control the transmis-sion of electricity, there are usually multiple busbars. These can be connected in many different ways.

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8 Lightning conductor mast

The lightning conductor mast is not part of the operating facilities of the substation. Nevertheless, it is an essential component. Given the often open area and the many tall metal devices, lightning strokes are not unlikely in a sub-station. In order to protect the devices and ensure the electricity supply, substations are equipped with sever-al high lightning conductor masts. Like a lightning rod on a house, it serves to conduct the lightning stroke to the earth in a controlled manner without exposing personnel and operating facilities to danger.

Protection against lightning strokes:

the voltage of a lightning stroke can amount to 100 million volts and has to be safely conducted to earth to avoid damage to the substation.

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Portal

Aside from operating facilities and lightning conductor masts, there is another noticeable construction within the substation – the portal. Overhead lines, busbars and trans-former connections cannot be suspended in thin air, but have to be supported in a mechanically stable manner. This purpose is fulfilled by the portals, which in case of a line or transformer portal look like a large frame in which the lines are insulated and suspended. Busbar portals, however, act as supports on which the tubular busbars are mounted and insulated.

Relay and operating buildings

Inside the substation there are also relay and operating buildings. Relay buildings mainly include protection and control components. In order to limit the distance to the controlled devices, there can be multiple relay buildings in-side a single substation. The operating building contains the other components of the control system, communications system and the storage, break and restrooms.

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Grid security 24/7

In the Transmission Control Centre, 50Hertz’s employees en-sure safe system operation around the clock. From here they control every line of the grid.

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In a substation, hand-held measuring instruments such as ones used in the home are insufficient. Here, the potential and current transformers provide the information needed to determine the state of the grid.

The control system monitors and manages the grid and gives an accurate view of the grid situation. It generates all the nec-essary data and sends this information to central posts over the communications network. The information related to the state of 50Hertz’s overall high-voltage transmission system is gathered by the Transmission Control Centre (TCC) in Neuenhagen near Berlin day and night and analysed by experts in real time.

Protection and control technology

Monitoring and protecting the substation

The protection and control system covers all equipment that is indirectly

involved in the process of power transmission.

The protection system guarantees the safety of the person-nel and the operating facilities. In case of a disturbance, like a short-circuit for instance, high currents are released. These endanger lines, transformers and other operating facilities. In order to avoid damage, these currents have to be interrupt-ed as soon as possible. If a disturbance is reportinterrupt-ed by the protection system, for example, the line in question can be disconnected very quickly. This happens automatically and the final consumer does not usually notice this interruption, as the electrical current arrives through another line.

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The need to build a new substation or to expand an exist-ing one is determined by regional changes in power con-sumption on the one hand and increasing feed-in of elec-tricity generated from renewable energy sources. A large number of criteria needs to be considered during the search for the proper location. The substation has to be built near a planned or existing line in order to avoid the necessity of a new overhead line. It is also important for the location to be easily accessible and a connection to the railway network should be possible, as the transformer is extremely heavy. Attention is also paid to the environmental aspect: nature re-serves are not considered for construction. Furthermore, substations must be built at a considerable distance from populated areas.

The construction of a substation is a time-consuming pro-cess, which can take anywhere from 1.5 to 4 years, depend-ing on the size of the station.

As soon as an appropriate site has been located for the new substation and the necessary applications have been sub-mitted within the scope of a detailed planning and approval procedure, the competent authority will grant its approval for the station’s construction if it is satisfied that all regulations laid down in the Federal Immission Control Act have been complied with. In addition to a building permit and other construction-related documents, this approval also includes a report on noise levels and on electric and magnetic fields. Before the construction begins, compensatory and

replace-Building a

substation

ment measures are planned and carried out to compensate the effects on nature and the environment.

The actual construction measures begin as soon as approval has been granted. First, the area is cleared and access ways are laid. After the property has been prepared for construc-tion, the foundation works are carried out for the portals and operating facilities. Relay and operating buildings are erect-ed. For the transformer foundations, special requirements apply: they have to include drain pipes and large separators that prevent oil from seeping into the soil or water in case of a transformer damage.

Roads are created inside the substation. These are neces-sary for future maintenance. In the next step, steel construc-tions are assembled, the operating facilities and the busbar are installed.

Power junctions for the energy transition

Transmission System Operators are responsible for the opti-misation, reinforcement and expansion of the electricity high-ways. They need to do this to adjust their grid to the new chal-lenges presented by the energy transition. This also requires higher capacity power junctions.

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When the substation is completed, all devices are tested pri-or to commissioning to verify that they function without er-ror. These tests are carried out according to a commission-ing plan. If everythcommission-ing works without problem, the substation can be put into operation. From this point on, the substa-tion is directly controlled by the Transmission Control Centre (TCC) in Neuenhagen near Berlin.

50Hertz The 50Hertz power junctions · 23

Safety first

This remote voltage tester was developed as an initiative by 50Hertz and is used in substations and switchgears. With this device, the voltage can be tested in a reliable and safe manner.

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Electricity requires voltage in order for the current to flow. The live lines

meet in the substations. However, these also contain operating facilities

that need to remain de-energized in order for them to function. That is why

these elements have to be insulated from the charged parts of the

installa-tion. Normal air is also a suitable insulator. It is the most frequently used

in-sulating medium in substations and switchgears.

Air- and gas-insulated

switchgears

The switchgears that use air as a means of insulation, are called air-insulated switchgears. These require enough space to create sufficient distance and thus enough insula-tion between the many different elements. This is reflected by the size of the construction site for air-insulated switch-gears: they measure several thousands of square metres and are usually found outside of towns or cities. Inside cities and their surrounding areas there are also households and industrial installations that require power. As high voltage is optimal for power transmission because of the minimal losses, the current is transported to the con-sumer at as high a voltage as possible and transformed to a low voltage (usually 230 or 400 volts) before it can be de-livered to the user. This means that even inside cities, there is a need for switchgears and substations. For urban sub-stations, gas-insulated switchgears are preferred. These in-stallations use a gas called sulfur hexafluoride or SF₆ as an insulating medium. Compared to air, the gas has better

insu-lating properties. As such, the distance between the individ-ual elements can be decreased significantly. The installation can be designed in a more compact way, then the air-insu-lated switchgears.

What are insulating materials?

Electric insulating materials have low conductivity. Their re-sistance to electricity is high, they are robust and are fur-thermore characterised by their low water absorbency. Among these insulating materials are porcelain, glass and several plastics.

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Inside a gas-insulated switchgear, only the conductor inside the chamber is charged. The conductor and the walls of the chamber are separated by the insulating gas. The chamber itself is earthed and is therefore safe to the touch. As a re-sult of this fully insulated design, the area surrounding the switchgear is free of electric and magnetic fields.

The gas-insulated switchgears and the SF₆ greenhouse gas have to be handled responsibly and with special care. Spe-cial safety regulations are in place. Maintenance is per-formed on a frequent and regular basis to avoid pollution. In 2005, 50Hertz signed the voluntary self-commitment by SF₆ manufacturers and users, and year by year reduces its consumption of SF₆ for the operation and maintenance of gas-insulated switchgears by a considerable amount.

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Substation platform in the Baltic Sea

The power cables of all turbines from the wind farm are bundled at this platform. From here, the platform is linked to the coast.

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Large offshore wind farms generate high volumes of electric-ity, which then need to be transported to land, where they can continue on their way towards the final consumer. But even on the high seas, substations are needed. To accom-modate these, offshore platforms are built. The power ca-bles of all wind turbines from a single wind farm are bundled at this substation platform. The voltage is transformed from 33 kV to 150 kV or 220 kV for efficient further transport. Operating an offshore substation comes with a high cost. As sea air is very humid, the hangar of the substation platform needs to have high-quality climate control and has to be de-humidified particularly well. By doing so, the same climate conditions are created as on land. Offshore substation plat-forms are constructed in a similar manner to onshore gas-in-sulated switchgears. Here, too, the SF₆ gas is used as an in-sulating medium due to the lack of space. The substation platform is also reinforced so that it is able to withstand the severe weather conditions encountered at sea.

Offshore

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Recent years have seen a resurgence in popularity for di-rect current, and Germany is no exception. The signifi-cance of high voltage direct current transmission (HVDC) is growing as it allows the transportation of large energy vol-umes across long distances at a limited loss, enabling a more targeted influence on power flows. Several new direct current power links will be used in Germany to connect the major wind power regions in the north to the consumption centres in the south.

Converter stations for

direct current connections

To integrate these power links in the existing power grid, which still uses alternating current, complex converter sta-tions are necessary to allow direct current transmission. These can be considered the „highway exit and entrance ramps“ for long-distance power transmission. They convert the current from alternating to direct current and control its transmission through the direct current lines. Investing in di-rect current transmission is especially advisable when large volumes of electricity need to be transported over long dis-tances (several hundred kilometres) with as little loss as pos-sible. Furthermore, direct current lines enable targeted con-trol over power flows. This is good for the stability of the electric system.

Over the years, alternating current became the standard rather than direct

current. The reasons for this are many. Alternating current can be

distribut-ed more easily over interconnectdistribut-ed lines, it is easier to switch and can be

easily transformed to other voltage levels. The advantages of the direct

cur-rent bring it back to the stage.

HVDC power transmission at 50Hertz

Together with a Danish system operator Energinet.dk, 50Hertz has been operating a 170-km long HVDC link for over ten years. The Kontek cable in the Baltic Sea connects the German and Danish grids. The cable reaches land in Bentwisch.

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Alternating current becomes direct current.

This is what the 50Hertz converter station in Bentwisch looks like on the inside. This imposing construction is called a con-verter tower and is needed to transform direct current to al-ternating current and back again.

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Active power is the energy that performs the work. In the case of a vacuum cleaner, it powers the suction. Reactive power, on the other hand, is needed to enable operation. In other words, it makes the engine run. Reactive power en-sures that there is enough voltage to keep the current

flow-Reactive power compensation by mechanically

switched capacitors with damping network

(MSCDN)

ing as well, in the same way as a water line needs to sus-tain enough pressure to keep the water flowing. An efficient solution to generate the required reactive power is the use of mechanically switched capacitors.

Most machines, from vacuum cleaners to newspaper printing presses, do not

only require so-called active power, but also reactive power.

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Phase shifting transformers

To better regulate power flows, phase shifting transform-ers (PSTs) are currently being installed in the east and south of the 50Hertz grid area. They will be located at the “inter-sections” with the neighbouring countries. When the phase shifting transformers shift the three phases of three phase current in relation to each other, the resistance of a line is increased. The current, which always chooses the path of least resistance, will flow elsewhere. Like valves on wa-ter conduits, phase shifwa-ters make it possible to control the load flow within the three phase current system in a targeted manner. The overloads on individual grid elements are thus avoided and transmission opportunities on individual lines in strained regions can be planned more efficiently and exploit-ed for power trading. This can only benefit secure system operation as well as electricity consumers, as more trade means more competition on the European electricity market and a tendency towards lower prices.

What is reactive power?

Not all of the electric energy can be used directly by the con-sumer. The reactive power is nevertheless needed to establish an electric field for the current and thus generate voltage. Reac-tive power is measured in Var.

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Electric and magnetic fields

Electric and magnetic fields abound in our own homes, even in nature itself. Our household appliances require power to function, and therefore generate electric and magnetic fields of their own. The Earth’s mantle also has its own magnetic field. Overhead lines and the operating facilities in a substa-tion similarly generate electric and magnetic fields.

Each substation in the grid area of 50Hertz is subject to care-ful examination to study its effects on the environment. For the construction of new substations or the expansion of ex-isting ones, the effects caused by electric and magnetic fields are determined with great scrutiny. The limit values laid down by the 26th ordinance on the implementation of the Feder-al Immission Control Act (BImSchG) have to be respected in each and every case:

- For electric fields: 5 kilovolts per meter (kV/m) - For magnetic fields: 100 microtesla (µT)

At an operating voltage of 1000 volts and an operating fre-quency of 50 Hz, these maximum values shall not be exceed-ed. The DIN VDE 0848 standard stipulates how to calculate the field strength and magnetic flux. Compliance with the limit values laid down by law is subject to stringent inspections.

Substations

and the environment

In actual practice, the immision values within a substation are up to 60 % less than the legal limit values. The effects outside of the substation are therefore also much more limited.

In daily life:

your average domestic power drill can generate a magnetic flux density of up to 800 microtesla at a distance of 3 cm to the human body.

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Noise

What does electricity sound like? The inner workings of a sub-station cause a constant deep buzzing sound with a 100 Hz frequency that can be heard inside the installation. The sound is in part created by the overhead lines leading to and from the substation, which release small discharges that emit a crackling noise, especially when the weather is humid. However, it is the transformer that is mostly responsible for the buzzing sound in the substation. The legally laid down immission values, which are stipulated in § 48 of the Federal Immission Control Act, also apply to transformers and other operating facilities:

It goes without saying that 50Hertz respects these limit values and ensures that during operation, noise levels are substantial-ly lower. Before a new substation is built, immission values and affected areas are approved by a competent authority and an acoustic survey is carried out.

Day Night

Purely residential areas 50 dB 35 dB

Mostly residential areas 55 dB 40 dB

Town areas and mixed areas 60 dB 45 dB

Even the most quiet household washing machine produc-es a volume of nearly 70 decibels, while a common refriger-ator generates a humming sound of approximately 35 dB. The noise levels inside a substation are therefore often low-er than active household appliances. Outside of substations, meaning on the outside of the fence, the volume drops even lower. A substation is a “quiet neighbour”.

Humming transformers

The iron core as well as the coils of the transformer are se-cured firmly in place. The forces of the magnetic field are so strong, however, that the elements are made to vibrate re-gardless. The alternating current has a frequency of 50 Hz. For each pulse, the direction of the current changes twice. This causes a change in the magnetic field, which in turn makes the metal components vibrate at a frequency of 100 Hz, producing a distinctive humming sound.

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Compensatory and

replacement measures

50Hertz handles water pollutants and industrial gases with great care, and properly disposes of waste materials. All lim-it values wlim-ith regard to immission control and nature con-servation are, of course, respected in the technical installa-tions. The actual values are often significantly lower. At the planning stage already, the installations have to meet high demands. Requirements are equally demanding during con-struction and operation. The environmental equipment of the substations is inspected on a regular basis and is replaced if needed. Noise control measures are also taken. Active en-vironmental management and continuous refresher training and sensitisation of the employees ensures a high level of environmental protection.

50Hertz plans and realises many compensatory and replace-ment measures with a view to nature conservation in order to compensate for the effects its installations have on the environment. For example, planting, ecological restoration of rivers and lakes and protective measures for endangered species, as well as the demolition or maintenance of build-ings that do not belong in the environment or which have become dilapidated, are carried out in close coordination with local partners.

A new home

For the expansion of the Hamburg-Nord substation, new forest areas of over 120,000 m² were created – twice the size of the area affected by construction. The effects on wildlife were also minimised. Moor frogs and natterjack toads, for instance, were relocated to an appropriate water body specifically created to this end before construction of the substation even started.

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An Elia Group company Contact

50 Hertz Transmission GmbH

Eichenstrasse 3 A · 12435 Berlin, Germany T + 49 ( 0 ) 30 5150-0

F + 49 ( 0 ) 30 5150-4477 info@ 50 hertz.com

Imprint

Published by : 50 Hertz Transmission GmbH Photos : Jan Pauls, Archiv 50Hertz, Alstom Concept and design :

Heimrich & Hannot GmbH