The third phase of the evolution of communication networks occurred in the 1970s and is characterized by the introduction of data networks and packer switching technology. To achieve compatibility between computers and packet-switched network ,the international Telegraph and Telephone Consultative Committee (CCITT from the French acronym established a word-standard protocol, called X.25 in 1976. This phase of networking is also characterized by the introduction and wide acceptance of local area networks(LANs). The invention of the laser (which stands for light amplification by simulated emission of radiation ) in 1959 led to major technical developments in the field of optical communication. 1970, Corning Glass Works reported on the first low-loss optical fiber (dopedsilica clad fiber ) that achieved 20 dB/km loss.
The fourth phase of communication networking ,which began in 1980, is
characterized by the availability of the integrated services digital networks (ISDN) and mobile communications.
With the development of national economy and people's living standards improve, people's growing demand for electricity, while the reliability and power quality of power supply put forward higher requirements. Feeder Automation is the reliability of power supply distribution network systems to improve the most direct and effective means of technology. Countries has increased in recent years on the city network and the transformation of rural power network, power supply bureaus of the major domestic investment in distribution automation is also increasing. Achieved in the distribution network automation process, we found that communication problems is a difficult problem. In this, just from the fiber-optic communication networks in automation applications with little knowledge about and experience.
2 Distribution Automation requirements for communication
SCADA system with the same dispatch, distribution automation system also needs an effective communication network, and he has his own characteristics: the number of terminals very much. System has a large distribution network by
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opening and closing, power distribution transformers, circuit breakers column to monitor these devices requires a number of FTU and TTU, while the FTU with the power distribution equipment installation, wide geographical distribution, communication nodes scattered.
Distribution automation system size, complexity and automation level of the decision of the communication system should meet the following requirements:
(1) Reliability:
Communications equipment distribution network systems have many exposed outdoors, bad environment, so must be able to withstand heat, cold, sun, rain, snow, hail and lightning and other natural attacks. Meanwhile, try to avoid all kinds of electromagnetic interference, to ensure long-term stable and reliable work, and asked when the line power failure, communication system can still work properly.
(2) economy:
Taking into account the overall economic power distribution system,
communication system, investment should not be too large, and strive to make full use of the existing main network communication resources, for the Lord, the overall distribution network planning, avoid duplication of investment.
(3) addressing large:
Communication system not only to consider the present and future data needs, but also consider the upgrade requirements.
(4) two-way communication:
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Distribution network automation to achieve the telemetry, remote, remote control, you must request a two-way communication capabilities.
(5) easy operation and maintenance.
According to the above requirements, along with fiber prices down, at present, optical fiber communication systems are widely used in electric power.
3 Optical Fiber Communication
Since the inception of laser and low loss optical fiber, optical fiber
communication system with its technical and economic advantages of the rapid rise of unparalleled, and swept the globe. The system is based on optical fiber as the transmission medium to light as the carrier signal to transmit information in communication systems, applications of light wavelength of 1.0 ~ 1.μm Jing, the entire system from the electrical side machine, Optical, cable and repeaters pose. Fiber can be divided into single-mode fiber (SMF), multi-mode fiber (MMF), long-wavelength low drive bulk fiber (LMF), polarization maintaining fiber (PMF) and plastic optical fiber (POF) and so are many; commonly used for single-mode and multi-mode fiber, multimode fiber is more than light transmission mode, and single-mode fiber transmission of a light wave mode only. Single-mode fiber multimode fiber transmission distance than the length, the current general, the optical signal in the multi-mode optical fiber to be available for about 6km, the single-mode fiber transmission within 30km. Therefore, the price of single-mode optical devices than multi-mode optical devices. Practical optical fibers are usually more to strengthen the core, protecting materials, fixed materials combined to form the transmission line cable.
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Fiber MODEM to be completed by optical signal and digital signal conversion between. Fiber MODEM generally have more than one data port to transfer synchronous or asynchronous signals. Communication speed up to 2Mbps or higher, with commonly used network communication rate is generally
synchronous asynchronous 19200bps N × 64K or less. It is sufficient to meet the needs of distribution network communication。
In addition, there is a double-loop fiber optic MODEM with self-healing func- tion. This feature greatly enhance the reliability of the communication. the signal is not affected, while the main station to send the appropriate alarm and positioning signals, so that maintenance personnel section of cable fault repair time.
4, the characteristics of optical fiber communication
Large capacity optical fiber communication with the communication, the attenuation is small, not afraid of lightning, anti-electromagnetic interference, corrosion resistance, confidentiality, reliability, and easy installation, but the relatively high investment costs, especially for inner city buried cable lines fiber laying, construction costs will be greater.
5, optical fiber communication implementations in distribution networks
Optical fiber communications network formation is very flexible and can frame into a star, chain, tree, mesh, single fiber network, dual-fiber network, ring multi-branch, multi-ring intersection, tangent, and other multi-ring topology network.
According to the characteristics of distribution automation systems, fiber optic ring net usually made up of network and computer local area network connection, data sharing.
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She Ji practical engineering, the fully take into account the special network topology power structure of communication complexity, SDH transmission systems can use up to 126 E1 (2M I) Quan cross Lian Jie He pairs the main branch of halo + more than the design of Si Xiang Guang. The basic framework of 1 to 3 SDH/STM-1 dual-fiber self-healing intersect or tangent, and when necessary, can change the way light card online upgrade SDH/STM-4. If the Bureau of the network control center is located in the geographical center of the LAN, the proposed design for the tangent to the ring to dispatch center as the cutoff point; if the Board deviated from the network control center LAN
geographical center of the proposed design for the intersection ring, because not dispatch center intersection, in order to reliably between the adapter ring, the ring at least two points intersect each other to protect routing.
6 Conclusion
In the actual distribution automation communication system, must build a low cost, high effective two-way communication system, with acceptable reliability and cost of information flow to provide very high performance. Also, because of distribution automation system functions to be accomplished by too many complex systems, a single communication system to meet the needs of all of the functions is unrealistic, and it is not economical. Therefore, power distribution automation system, to apply a variety of communication methods, according to a comprehensive economic and technical indicators and selecting the best combination of them. In the power system more commonly used multiple means of communication also point digital microwave radio data transmission, wireless spread spectrum, green cables, posts and telecommunications local network, carrier, Spread Spectrum, etc., for the selection network.
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