The invention relates to the field of substation automation, control and monitoring. It relates to a substation with a communication device for transmitting signals between a control unit of the substation and a control unit of a bay of said substation and it further relates to a method for transmitting a signal between a control unit of a substation and control units of bay elements of said substation.

The main function of an electrical substation Is to transfer and transform electrical power. A typical substation comprises a control unit and one or several bays consisting of one or several bay elements.

The substation control unit usually comprises a control room from where a person can monitor and control the substation.

The bays usually comprise bay elements such as disconnectors, circuit breakers, transformers etc. These bay elements are called primary appliances. On a single bay several different or similar primary appliances can be installed. Such primary appliances are connected to a control unit, which regulates, controls and monitors the primary appliances.

For controlling and monitoring purposes, the control units of the bay elements have signal network connections between each other and to the substation control unit, via which e.g. signals from the control units and real-time data of the primary appliances are transmitted. Control units also may have communications interfaces to which a service computer can be connected and via which service-relevant status data and measurement data are transmitted. The communications interfaces are used to allow a service computer to be connected to the controller in the event of a fault or during maintenance of the primary appliances. Data stored in the controller can then be read out by means of the service computer in order, for example, to determine the cause of a fault, or in order to analyze a state of the primary appliances.

High currents and voltages cause interference and electromagnetic noise in the vicinity of the substation. The low level signal connections between the control units need special attention regarding electromagnetic shielding against said noise.

Fiber optics are secure in terms of interference and therefore often used for communication purposes within substation. Besides their resistance against electromagnetic interference fiber optics have the advantage of being electrical nonconductive. There is therefore no direct electric connection between two devices connected by fiber optics. The disadvantage of fiber optic signal connections is their complicated handling and the fact that a party line (bus) is hard to implement with fiber optics only. This means that for every bay of a substation or even for each bay element with its own control unit a dedicated fiber is needed, leading to an immense bay wiring effort.

The invention relates to such a substation and substation communication system, as described above and as is disclosed in the article by G. Schett et al., "Die intelligente GIS - grundlegender Wandel in der Kombination von Primär- und Sekundärtechnik", ABB Technik, Ausgabe 8/1996, S.4-14 . The data lines needed for the control and communication technology are made of conductive wires and/or of fiber-optic connections. For redundancy purposes doubled data lines can be provided.

Wireless Local Area Networks (WLAN) as e.g. described by the IEEE 802.11 standard use e.g. electromagnetic radio frequency waves, to communicate information from one point to another without relying on any physical connection. Radio frequency waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end. This is generally referred to as modulation of the carrier by the information being transmitted. Once data is modulated onto the radio carrier, the radio signal occupies more than a single frequency, since the frequency or bit rate of the modulating information adds to the carrier.

In a typical WLAN configuration, a transmitter/ receiver (transceiver) device, called an access point, connects to a server or a wired network. At a minimum the access point receives, buffers, and transmits data between the WLAN and the server or the wired network infrastructure. Other components access the WLAN through WLAN-adapters. These adapters provide an interface between the components operating system and the airwaves via an antenna.

Signal connections and networks via radio frequency system give a maximum of flexibility and reduce the costs for wiring. State of the art radio frequency systems like Bluetooth, Wireless LAN or DECT allow short-range, point-to-multipoint data transfer. Their nominal link ranges are from 10 cm to 10 meters, but can be extended to 100 meters by increasing the transmit power.

But common radio frequency systems still have a rather low reliability caused by general-purpose interference. Manufactures of such systems try to increase the system availability and reliability by using intelligent modulation and coding systems (e.g. FHSS (Frequency Hopping Spread Spectrum) or DSSS (Direct Sequence Spread Spectrum)).

Nevertheless, transmission of critical signals in the presence of severe interference, as it can appear in a substation, via radio frequency systems is still not generally accepted.

In the WO 94/14252 a communication system is described, in which the transmission of electromagnetic waves in the interior of buildings is shielded against in-building radio interference. For this purpose several rectangular waveguide segments are connected together to form an enclosed transmission medium. A plurality of transceiver devices are coupled to the transmission medium for in-coupling and out-coupling of radio waves. The waveguide segments are integrated into modular fumishing, such as partitioning walls, desks, tables and cabinets.

In the JP 10266629 radiocommunication with the same frequency is practiced inside a building by partitioning the building into rooms that are shielded electromagnetically. Several such rooms are connected together by means of a waveguide to form a zone.

One object of the invention is therefore to provide a substation with an improved and simplified communication device for transmitting signals between control units of the substation and to provide an improved and simplified method for transmitting a signal between control units of a substation.

This object is achieved by a communication device, together with a method having the features of patent claims 1 and 17, respectively.

In one embodiment, the present invention is a substation with a communication device comprising a first transceiver with an antenna for sending/ receiving radio frequency signals connected to the substation control unit, second transceivers with antennas for sending/receiving radio frequency waves connected to the bay element control units and a waveguide for transmitting said radio frequency waves enclosing the antennas of said first and second transceivers. The waveguide shields said radio frequency waves from interference in the vicinity of the substation, and also shields, or at least attenuates, the environment from electromagnetic emissions caused by the sender. This allows to even increase transmission power beyond levels that are normally used for non guided applications, or to use frequencies out of normal bands and therefore an increased bandwith can be used.

Since several bays or bay elements are usually physically side by side their control units can easily be connected by one waveguide enclosing the several antennas. With very little effort a wireless party line (bus) can be realised. Also, additional bays or bay elements can be added to the party line by simply extending the waveguide. No extra wiring is needed. The wave guide can be an integral part of a bay or of a bay element, so the party line can be extended, by just placing the bay or the bay element in the right place.

Best shielding against interferece is achieved with a tubular wave guide with a rectangular profile. On one side of the rectangular profile the wave guide has an opening through which the antennas are stuck into the interior of the wave guide. On both sides of the opening radiation protections are designed to improve shielding and reduce radiation. The radiation protections are preferably longer than the lengths of the opening in order to minimise radiation.

In another embodiment, the present invention is a method to transmit the signals between the control unit of the substation and the control units of a bay or of a bay element. Said signal is first frequency modulated in the first transceiving device, is sent into the wave guide as a radio frequency wave, and is then received by the second transceiving device, in which the control signal is converted back into an electrical signal, which is then finally processed by said bay control unit.

Details and advantages of the present invention will become more fully apparent from the following description, the claims and the accompanying drawing in which

Fig. 1

shows a part of a substation with switchgear bay elements and a communication device with transceiver devices according to the invention, and

Figs. 2 a/ b

show an enlarged view of two transceiver devices according to Fig. 1.

Fig. 1 shows a possible embodiment of a part of a substation with three bay elements 1 that are located on a bay and a substation control unit 4. The switchgear devices 2 are connected to the three phases of a primary transmission line 10 and a secondary transmission line 11. Instead of switchgear devices, other so called primary appliances like transformers could be installed on the bays. The primary appliances need not to be the same on all the bays and the number of bays or bay elements is in no way limited to three or less.

Each of the bay elements 1 has a control unit 3 to control and monitor the primary appliances. The bay element control units usually comprise a processor unit, a memory for storage of monitoring data and some kind of an interface, e.g. for maintenance purposes, and/or a protection relay

The substation control unit 4 comprises a computer-based server (and/or protection relay), which is network connected to the bay element control units 3 in order to exchange data and control signals. Connected to the server of the substation control unit as shown in Fig 2 b is a transceiving device 7, which serves as the access point of a wireless network. Attached to the access point is an antenna 9 for sending electromagnetic radio waves with superimposed data signals.

The bay element control unit 3 is connected to an other transceiving device 6 with an antenna 9 as shown in Fig. 2 a for sending and receiving control and real-time monitoring data signals. This transceiving device 6 is a wireless network adapter that serves as an interface between the airwaves and the bay element control units processor unit.

In order to shield the transmitted signals against interference 12 a waveguide 5 is connecting the antennas 9 of the transceiving devices 6 and 7 The waveguide has basically a tubular shape with a rectangular profile. On one side the waveguide 5 has an opening through which the antennas of the transceiving devices 6 and 7 are stuck into On both sides of the opening radiation protections are arranged. The length t of the radiation protections is longer than the length s of the opening in order to keep the radiation on a negligible low level.

The waveguide 5 is mounted onto the control units with holders 8 as shown in Figs 2 a and 2 b

In most cases the waveguide connects bay element control units that are physically side by side. Even if the control units are not 100 per cent in line or there is some displacement between the dedicated devices it is possible to communicate in a reliable way. The wave guide needs to have no complicated design and is very easy to install.

Any electromagnetic shielding material can be chosen for the wave guide, eg aluminum or copper.

Reliable waveguides for a broad band of frequencies can be designed.

Typical values of such a waveguide are width a of waveguide = 0.1 m height b of waveguide = 0 05 m length s of opening = 0.03 m Frequency = 2-3 GHz Attenuation = 14 dB/km Coupling Attenuation = 4-6 dB Material = Aluminum Profile

The waveguide 5 not only keeps interference out but it also makes sure the radio wave does not or only to a very limited extend propagate outside the waveguide. Therefore basically all frequencies that physically make sense can be used for this kind of communication, particularly others than the very narrow unlicensed 24 GHz frequency band which is used for state of the art WLAN systems. By using two or more different frequencies very high data rates can be achieved without having to somehow split a frequency in one way or another.

One possible setup could e.g. comprise transmission of real time data at 2 GHz, synchronisation impulses at 2.5 GHz and the normal monitoring data at 2.4 GHz.

By using more than just one frequency at the same time a very good real time synchronization is achieved along with a high redundancy.

The communication device according to the invention is simple to extend to additional bays or bay elements without any inter bay wiring.

Thanks to the state of the art wireless network protocols high bandwidth communication party lines (buses) can easily be implemented.

Any state of the art or upcoming commercial wireless standard technology can be used in the communication device according to this invention.

While in Highvoltage-Substations communication between bay element control units of different elements of a bay (intra-bay) is necessary, in Middlevoltage-Stibstation this communication can be reduced to bay-to-bay (inter-bay) communication between bay control units and the substation control unit

1

Switchgear bay element

2

Switchgear

3

bay element control unit

4

substation control unit

5

wave guide

6

transceiver, WLAN-adapter

7

transceiver, WLAN access point

8

mounting device, holder

9

antenna

10, 11

power lines

12

electromagnetic noise, interference

a, b, s, t

Dimensions