The only connection between the dam and the control station is given by the power cable. Checking as well as remote activation are also possible thanks to the Powerline communication.
In telecommunications, the powerline is a technology for the transmission of voice or data that uses the power supply network as a transmission medium.
It is achieved by superimposing on the transport of electrical current, continuous or alternating at low frequency (50 Hz in Europe and most of Asia and Africa, 60 Hz in other regions of the world), a higher frequency signal that is modulated by information to be transmitted. The separation of the two types of current is carried out thanks to the filtering and separation of the frequency ranges used.
The technique has been used for decades, before the introduction of mobile telephony, for transmissions with running trains (using power lines, for example from Telettra), to control electrical devices via its power supply network, to read electrical meters remotely , for home intercom systems etc. The same operator Terna uses (and has used in previous decades) the network to transmit telecontrol and telephony. More recently it is used to give access to data (for example the Internet) to homes via the power supply without the need for specific access by coax or radio.
This technology is used for home automation with the use of various standards.
The older ones such as the X10 (prevalent in the United States) allow limited bandwidth transmissions and are dedicated to simple home automation such as turning on lights or setting up burglar alarm systems. They require the installation of appropriate interface modules inside the sockets and controls. The advantage over traditional systems is, in addition to saving part of the wiring, the ability to easily modify the operation of the system and the ability to achieve “intelligent” features.
A powerline technology widespread all over the world and also in Italy is based on the LonWorks protocol, now also ISO 14908-1-2-3-4 standard, in fact on this protocol is based the counter that Enel has been installing for some years capable of remote reading and contract modifications.
Recently a new domotic system in powerLine technology, called “PowerDom”, has been proposed on the market, by D-Tech Electronic srl, which uses, for data communication, a FSK modulated signal with a variable frequency between 66 kHz and 132 kHz and speed data transmission of 4 800 bit / s. Furthermore, the communication protocol provides an effective error control and correction algorithm able to make the communication reliable for the realization of all the functions of a class 1 home automation system: technical alarm and intruder alarm system, access control, control remote GSM, light control and air conditioning, user management and energy saving, lights and blinds automation.
In the context of local networks for homes and / or small offices, the HomePlug consortium has been created that allows the creation of the equivalent of an Ethernet network through the use of the normal household electrical system. The HomePlug specifications in version 1.0 provided a theoretical maximum speed of 14 Mbit / s, which resulted in an actual of 5-6 Mbit / s. Subsequently, non-standard extensions were released which provided for a theoretical maximum speed of 85 Mbit / s and an effective range of 16-25 Mbit / s with similar performance, therefore, as provided by 802.11g wireless solutions. Since October 2006 the HomePlug AV standard has been introduced, which supports a theoretical speed of 200 Mbit / s with an effective variable between 70 and 110 Mbit / s. With this transmission system it becomes possible to use services such as high definition video streams that were not possible before. As for wireless systems, the actual speed depends on many factors such as the quality of the system, the structure, the presence of any sources of disturbance on the electrical system.
Public utility companies use pairs of capacitors (with which high-pass filters are implemented) to connect low-frequency radio transmitters to electrical conductors of the electric network. The frequencies used range from 30 to 300 kHz with amplified transmitters that elevate the signal to hundreds of watts of power. These signals can be diffused on the high voltage lines from one to three conductors and each high voltage line (with one, two or three conductors) can support many powerline communication channels.
Filters are applied to the substations to prevent the carrier frequencies from passing through the equipment of the control panel and to avoid that transmission errors due to distance do not affect even isolated segments of the network.
These circuits are used for the control of switching devices and for the protection of transmission lines.
For example, a protection device can be used to free a line if an error is detected between its two terminal nodes, or to let it operate if the error affects all transmission lines (and does not depend on individual nodes, but on network). On one hand the operators use low voltages and, increasingly, the optical fiber; on the other hand, powerline is a low-cost solution in cases where an optical fiber excavation is not economically viable.
Powerline modems transmit on medium-high frequencies (1.6 to 30 MHz). The asymmetric speed in the modem is 256 kbit / s against 2.7 Mbit / s in download. On the repeater placed in the electric meter the speed is 45 Mbit / s and can be connected to the 256 kbit / s modem. In medium-voltage stations, the speed up to the Internet is 135 Mbit / s. Unlike the United States, in Europe hundreds of houses are connected to the same substation with the advantage of not requiring the adaptation of many power plants, but with the disadvantage of a much more fractional and low band. The powerline is presented as an alternative technology to the twisted pair, although it could technically be used for the connection between medium and low voltage power plants. However, the copper telephone twisted pair is a cable that is the same as the electrical cable that pushes electric operators to use their own network rather than using external infrastructures. This solution would theoretically provide broadband access and thus reduce the digital divide in those areas where the ADSL is struggling to arrive or where the access to the optical network envisaged for future Next Generation Network would seem in the first place impossible for these areas.
The powerline can be used to bring broadband to those users that are interposed to the wireless network from trees, walls or other obstacles to the signal. Rather than locating the repeater at the top if there is a sufficiently high point, or an unlikely trellis to serve a single user, it is less expensive to connect to the nearest wireless repeater a “converter” that sends the signal over an electrical cable, even if the The wireless device is far from the low voltage cabin (and the powerline equipment must be placed in a special cabin). Italy has 7 500 km of electric cables, one of the largest networks (for the choice of a centralized energy production): it is probable that even in the presence of an inaccessible place or isolated houses an electric cable is available for powerline .
In addition to reaching the most difficult-to-service utilities with powerline, the hybrid network has the advantage of making it acceptable to cover low-voltage power lines. The optical fiber is saved by connecting the low voltage power plant with a series of radio links to the media center which is wired with optical fiber. Unlike sending a copper cable, the wireless signal maintains high quality and low latencies even over long distances if signal correction software is present in the repeaters.