DE102014222598A1 - Disconnecting faulty network sections of a low-voltage network from other network sections - Google Patents

Abstract

A method for separating faulty network sections of a low-voltage network from further network sections of the low-voltage network is characterized in that a plurality of network sections are each separated by a power switch (5, 6), wherein adjacent power switches (5, 6) with each other for determining a line difference in wireless data connection (8) and disconnect the network section between them from the low-voltage network when a predetermined error value corresponding to the difference of the currents flowing through adjacent circuit breakers (5, 6) is exceeded. This can be a large-scale failure of the power supply can be reduced in case of failure.

Description

Technical area

The invention relates to a method for separating faulty network sections of a low-voltage network from other network sections of the low-voltage network.

Low-voltage networks are part of the electricity distribution network that distributes electrical energy to most of the final electrical consumers, which consists of low-voltage equipment. In order to avoid voltage losses, low-voltage networks are limited in the spatial extent to a range of some 100 m to a few kilometers. They are therefore fed regionally via transformer stations (local network stations) from a superordinate medium-voltage network. They are usually operated in Europe with a mains voltage of 230 V (between each outer conductor and the neutral conductor) or 400 V (between the three outer conductors), but in any case only up to 1000 V. Rated outputs of individual local power transformers may vary depending on the destination grid planning of the respective distribution system operator, but are typically 250 or 400kVA for rural areas and 630 or 800kVA for inner city areas.

Traditional grid operation is facing great challenges due to the increasing penetration of decentralized, mostly renewable energy generation plants (DEA) as well as the increasing development of electromobility. For example, a decentralized power generation plant (DEA) is a photovoltaic system or wind turbine.

State of the art

In recent years, there has been a trend towards so-called "smart grids" which, as intelligent power grids, comprise the communicative networking and control of power generators, storage devices, electrical consumers and network resources in energy transmission and energy distribution networks of the electricity supply.

Network stability in energy transmission and distribution grids can be divided into two main problem areas: The predominant problem in rural energy distribution grids is the voltage level, which is also called the "U problem". In urban power distribution networks, which tend to have low line lengths due to the load density, it is not the voltage maintenance that is more prevalent but the problem of equipment utilization. This is also called the "I problem". Decentralized feeders initially reduce the high utilization of lines and transformers. In the rarest cases, however, the performance limits in the feedback are violated. Probably the bigger problem can cause uncoordinated, additional loads by charging electric vehicles.

In addition, for example, in suburban areas, network sections within a network area may have both a rural and an urban character. To the last participant still by the standards (for example, by the 50160 ) to comply with specified voltage limits or not overload the resources, either network operation must be operated or an active network management system must be used. The latter specifically targets producers, flexible consumers or even storage facilities in the energy distribution network in order to maintain grid operation in accordance with the standards.

For urban networks, an additional solution is to mesh the networks. This is possible due to the fact that the historic growth of electricity grids, especially in urban areas, leads to a large number of mostly openly operated coupling points that can be closed for meshing. As a result, the short-circuit power in the grid area is increased and the described effects are largely reduced. In practical terms, this significantly reduces the overall impedance, resulting in the so-called "copper plate", which is often cited.

The problem now is the treatment of this meshed network in case of failure. A mesh network in electric power engineering is a special form of power network, which in the topology is determined by a multiplicity of knots and meshes. As a rule, mesh networks have several feed-in points and distribute electrical energy over several connecting lines to the individual consumers. In addition to the high short-circuit power that must be mastered in meshed networks, the selectivity suffers in the event of a fault and thus the number of affected customers increases. Normally, the protection concept in low-voltage networks consists of fuses (= overcurrent protection device, which breaks the circuit when the current exceeds a certain value for a sufficient time by melting a fused conductor) or non-directional protective relays at the outgoing busbars of the transformer station of the corresponding low-voltage network. In the event of an error, this means that the fault location can not be switched off selectively. Instead, the entire network area must be switched off and the troubleshooting started.

An opposite problem arises with island-capable microgrids. A microgrid is generally a group of generators, memories and loads that are usually network-connected to higher-level networks, but can become autonomous in the event of major disruption or market incentives.

In off-grid operation, where the supply is provided by distributed power generation systems (DEA), the available short-circuit power decreases in the event of a fault. DEA are usually only able to deliver 1.1 to 1.2 times the rated current in the event of a fault. As a result, the necessary short-circuit current for rapid release of the standard fuse used can not be delivered.

Since the usual protection concept for low-voltage networks is therefore passive, large-scale failures would arise in intermeshed operation in the event of a fault. In island operation, the errors could no longer be reliably resolved in the case of large blackouts.

At the beginning of the electrical power supply, the concept of meshing was quite the practice and has only recently been resolved by separation into e.g. replaced open double rings. The advantage lies in the fact that this makes it possible to react much more selectively to faults and also provides structural safety (if one line section fails, all customers can be immediately re-supplied from both sides after switchover) in low-voltage networks.

Particularly in high and medium voltage networks, active concepts of network protection are already used for meshed operation. Network protection describes the technical precautions that protect the electrical energy transmission network from the effects of faults (short circuit, ground fault) in individual power supplies. The line protection devices measure the current via the current transformer and / or the voltage via the voltage transformer. They distinguish the fault from normal operation. If the error is detected, then the associated circuit breaker is switched off and thus the faulty network segment is disconnected from the rest of the supply network. This will thus be protected from the effects of the error.

Thus, in medium and high voltage networks usually distance protection devices or UMZ protection devices are used. With a DEV protection (independent maximum current time protection), when a set current amount is exceeded, eg. B. 400 A, after the associated delay time issued a signal to turn off the circuit breaker. The delay time is independent of the actual flowing current. In the case of existing message paths, line differential protection devices are also used. In contrast to the distance and overcurrent protection devices, these are strictly selective, they each have a protection range between two current transformers (or both on each side of the current transformer).

For line differential protection, the currents are determined on both sides of the circuit breaker. The sum of the inflowing streams should be equal to the sum of the outflowing streams. If this basic requirement is not met, the protection triggers. A message path is used to transmit the measured value of the current from one side of the line to the other side. Thus, both protection devices know their own and the power of the remote station. If a difference is detected here, the line is switched off via the assigned circuit breaker. Digital protective devices can usually be operated as a UMZ protection in case of failure of the message path. However, then lacks the strict selectivity of the line differential protection. In addition, distance protection and / or UMZ protection devices on both sides of the line are often used as back-up protection for the line.

In principle, directional overcurrent time protection (UMZ-R) would also be possible, for example by means of selectivity via staggering of the tripping time and the direction information, but this is only truly selective if the topology of the voltage network remains the same. However, this is not the case with medium-voltage and in particular low-voltage networks, which would result in corresponding engineering expenditure.

In addition, there are no communication links between the protection devices for directional differential protection in low-voltage networks. Creating your own physical data connections would not be profitable.

Presentation of the invention

An object of the present invention is to provide a network protection solution which, for both meshed low-voltage networks and autonomous low-voltage networks (island operation), reduces large-scale power failure in the event of a fault.

This object is achieved by a method having the features of patent claim 1 and comprises a method for separating faulty network sections of a low-voltage network from further network sections of the low-voltage network, wherein a plurality of network sections are each separated by a power switch, wherein adjacent power switches to each other to determine a line difference in wireless data connection and disconnect the network section lying between them from the low voltage network when a predetermined, a fault corresponding difference value of the currents flowing through adjacent circuit breakers, is exceeded.

It is therefore proposed to provide an intelligent low-voltage circuit breaker including protection functionality, where by "intelligent" it is meant that the individual circuit breaker has so much knowledge about its environment and the laws therein to clarify a fault with its neighbors and all power switches according to the invention collectively ensure reliable network operation. The structure of the circuit breaker for the inventive method thus corresponds to a multi-agent system in which various agents in loose coupling pursue a higher-level goal - the network protection.

Functionally, this means that two adjacent circuit breakers each form a line differential protection to allow a selective shutdown of faults in (partially) meshed low-voltage networks or island-capable microgrids. The circuit-breaker can be modeled as an agent having the following resources: measuring the currents on the connected lines, operating the disconnecting switches for these lines.

• – topologische Information über die benachbarten Leistungsschalter
• – Stromdurchsatz durch die benachbarten Leistungsschalter. Er kann darüber hinaus noch über folgendes Wissen verfügen:
• – Belastungsgrenzen der angeschlossenen Leitungen
• – technische Informationen über die benachbarten Leistungsschalter, wie Reaktionsgeschwindigkeit
• – gegebenenfalls Informationen, wie Topologieänderungen betreffend die benachbarten Leistungsschalter erkannt werden können.

A circuit breaker according to the invention will consequently have at least the following knowledge:

• - topological information about the adjacent circuit breakers
• - Current throughput through the adjacent circuit breakers. He may also have the following knowledge:
• - Load limits of the connected cables
• - technical information about the adjacent circuit breakers, such as reaction speed
• If appropriate, information on how topology changes relating to the adjacent circuit breakers can be detected.

If the circuit breaker has all the points of knowledge listed here, it can autonomously make all decisions that fall within the scope of line differential protection.

By using wireless communication, it is not necessary to provide physical data connections between the circuit breakers.

For the application of the method according to the invention, it must be determined which circuit breakers are assigned to the two line ends of a network section, that is to say which circuit breakers are considered to be adjacent with respect to a specific network section. There are at least three options for this:

First, it can be provided that the definition of which circuit breakers are adjacent and in wireless data connection with one another for the purpose of determining a line difference is effected by a point higher than the circuit breaker and is not changed by the circuit breakers. This embodiment can be used for initial pilot applications or demonstrations, or if it is ensured that no topological changes occur. The superordinate body is then usually a specialist who enters the definition manually. The determination can then only be changed manually by a specialist. For a practical, namely permanent, use in many low-voltage networks, this option is not suitable due to the high engineering effort.

The second possibility is that the determination of which circuit breakers are adjacent is performed by a higher-level circuit breaker and a circuit breaker on assignment of a new adjacent circuit breaker a wireless data connection to the new adjacent circuit breaker for the purpose of determining a line difference builds. In this embodiment, a circuit breaker receives at least those topology changes that leads to a change in its neighbors, communicated from a central system, such as a so-called geographic information system GIS. As an intermediate, an intelligent local network station (iONS) can ensure the transmission of the relevant neighbor changes. If the information transfer concerning the topology change is sufficiently fast, the power switch can itself respond to this change of the neighbor and establish the necessary data connection to the new neighbor.

In order to achieve the most independent possible configuration of the method according to the invention, it is provided in a third embodiment that the definition of which circuit breaker is adjacent, by the respective circuit breaker and a circuit breaker when assigning a new adjacent circuit breaker for the purpose of determining a line difference, a wireless data connection to the new builds adjacent circuit breaker.

So there is an independent neighbor detection by the individual circuit breaker. The circuit breaker determines its communication technology neighbors and agrees this information with that about its so-called "electrical" neighbors. If there is a topology change, so there is a new circuit breaker as a neighbor, a neighbor detection is carried out (ie, for example, the technical information on the new adjacent circuit breaker determined) and the corresponding data connection established accordingly. For the methods for neighbor detection fundamentally different methods are possible.

The second and third characteristics offer the advantage of selectivity over a UMZ-R solution due to the functionality of the line differential protection.

In particular, the third expression leads in the direction of automation of the low-voltage network, because the line switches in the sense of "plug and play" without manual engineering effort can be inserted into the low-voltage network.

With the method according to the invention, with regard to the desired automation of low-voltage networks, an additional functionality can also be provided in that a message is sent to a higher-level regulatory authority of the low-voltage network even when a network section is overloaded. Thus, the I-problem mentioned above can be taken into account, so an overload detected (and this counteracted if necessary) before an error occurs.

The method according to the invention will generally be performed computer-aided. Accordingly, the subject invention can also be implemented as a computer program product comprising a program and directly loadable into a memory of a circuit breaker of a low-voltage network, with program means to perform all the steps of the inventive method when the program is executed by the circuit breaker.

The invention also encompasses a low-voltage network with at least one circuit breaker according to the invention for disconnecting faulty network sections of the low-voltage network from further network sections of the low-voltage network for carrying out the method according to the invention. The low-voltage network is characterized in that the circuit breaker is in wireless data communication with an adjacent circuit breaker for determining a line differential and includes a disconnecting device configured to disconnect the network section between the two circuit breakers from the low-voltage network, if a predetermined one, a fault corresponding difference value of the currents flowing through the adjacent circuit breaker is exceeded.

Brief description of the figures

To further explain the invention, reference is made in the following part of the description to the figure, from the further advantageous embodiments, details and further developments of the invention can be found. The figure shows a schematic representation of a meshed low-voltage network.

Embodiment of the invention

The Fig. Shows a meshed low-voltage network, such as a local area network, with three network stations 1 . 2 . 3 , Every network station 1 . 2 . 3 is represented by a transformer, from its busbar 4 depart each three electrical lines. In this case, the electrical lines of the low-voltage network are shown as solid lines, in contrast to the data connections shown dashed lines between the individual circuit breakers. The circuit breakers are shown as small circles, the inventive method based on two adjacent circuit breakers 5 . 6 , is explained.

The between the adjacent circuit breakers 5 . 6 lying electrical line forms a network section, by means of the circuit breaker 5 . 6 could be separated from the rest of the low-voltage network. This network section has a fault 7 on. About the between the circuit breakers 5 . 6 existing data connection 8th Now the current throughputs of the other circuit breaker are continuously transmitted and compared with their own power flow. If this results in a difference value that corresponds to a fault (earth fault or short circuit), the disconnecting devices of both circuit breakers switch 5 . 6 the intervening network section from the network.

The data connection between the circuit breakers must generally be robust to ensure the ongoing determination of a line differential. The easiest way is to use standardized data connections.

Moreover, for the third embodiment of the method according to the invention, it is still necessary for the circuit breakers to recognize each other as neighbors and for a circuit breaker to assign the respective neighbors to the network sections originating from it. For this it is necessary to establish a fast connection ensure peer-to-peer communication between the circuit breakers and / or multi-hopping. Multihopping is the simultaneous transfer of data from multiple nodes or devices in a network to a specific node.

The data connection should be able to determine the line difference continuously with little effort (with low "base load"), but have good availability in the case of topology changes. At the range of the data connection, no high demands to make, it is sufficient a maximum range of 1000 m or a line of sight connection (line connection).

The data link or units that provide them should be retrofitable to existing circuit breakers.

The data connection could be approximately with the 802.11p standardized extension of the WLAN standard and with the ETSI G5 standardized geonetworking. However, the frequencies used would not be in the frequency range of 5.9 GHz reserved for IST applications, but in the normal WLAN frequency range of 2.4 or 5.6 GHz according to 802.11abg. These extensions allow you to build a meshed wireless network without a dedicated master and with minimal base load (no beaconing). The communication can take place at any time without BSSID (the Basic Service Set Identification (BSSID) uniquely designates every Basic Service Set (BSS) of a WLAN): according to the 802.11p speech, ie "OCB" - "outside the context of a BSSID".

LIST OF REFERENCE NUMBERS

1

 first network station

2

 second network station;

3

 third network station;

4

 bus

5

 first circuit breaker

6

 second circuit breaker

7

 fault location

8th

Data connection between first and second circuit breaker 5 . 6

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• EN50160 [0006]
• ETSI G5 [0042]

Claims (8)

Method for separating faulty network sections of a low-voltage network from further network sections of the low-voltage network, characterized in that a plurality of network sections are each connected by a circuit breaker ( 5 . 6 ), with adjacent power switches ( 5 . 6 ) with each other for determining a line difference in wireless data connection ( 8th ) and disconnect the network section between them from the low-voltage network, if a predetermined error value corresponding to the difference of the currents passing through adjacent circuit breakers ( 5 . 6 ), is exceeded. Method according to claim 1, characterized in that the definition of which circuit breaker ( 5 . 6 ) and in order to determine a line difference with each other in wireless data connection ( 8th ), by one of the circuit breakers ( 5 . 6 ) and is not changed by the circuit breaker. Method according to claim 1, characterized in that the definition of which circuit breaker ( 5 . 6 ) are connected by a circuit breaker ( 5 . 6 ) and a circuit breaker when allocating a new adjacent circuit breaker a wireless data connection ( 8th ) to the new adjacent circuit breaker for the purpose of determining a line difference. A method according to claim 3, characterized in that the higher-ranking point comprises a local network station. Method according to claim 1, characterized in that the definition of which circuit breaker ( 5 . 6 ) are adjacent by the respective circuit breaker and a circuit breaker when assigning a new adjacent circuit breaker for the purpose of determining a line difference a wireless data connection ( 8th ) to the new adjacent circuit breaker. Method according to one of Claims 1 to 5, characterized in that a message is sent to a higher-level regulatory authority even when a network section is overloaded. Computer program product comprising a program and directly into a memory of a circuit breaker ( 5 . 6 ) of a low-voltage network, with program means to carry out all the steps of the method according to one of claims 1 to 6, when the program from the circuit breaker ( 5 . 6 ) is performed. Low-voltage network with at least one circuit breaker ( 5 . 6 ) for separating faulty network sections of the low-voltage network from further network sections of the low-voltage network for carrying out the method according to one of claims 1 to 7, characterized in that the power switch ( 5 . 6 ) with an adjacent circuit breaker for determining a line difference in wireless data connection ( 8th ) and a separating device which is designed so that the between the two circuit breakers ( 5 . 6 ) is disconnected from the low-voltage network when a predetermined, a fault corresponding difference value of the currents flowing through the adjacent circuit breaker, is exceeded.

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