1 Introduction
During the 30 years of reform and opening up, with the continuous advancement of the market-oriented reform of the power system, the State Grid Corporation of China, as a national energy security and national economic lifeline, has proposed the strategic goal of building "one strong and three excellent". In order to build a harmonious society with sustainable development and better achieve energy saving and emission reduction, the step of implementing the tiered electricity price policy has been approaching. The real-time collection of power users' electricity consumption information is an important technical means for the implementation of this policy.
Through the construction of the user's electricity information collection system, the online monitoring of the metering device and the real-time collection of important information such as user load, power, voltage, etc. can be realized, and the power user information can be controlled in a timely, complete, and accurate manner. Three important parts, the construction of business master station system, user information collection, and data communication system must fully consider how to meet the demand for real-time collection of user electricity data. Among them, the data communication system is more useful as a transmission channel for user electricity data. The key is to choose the most appropriate technical means to ensure the safe, reliable and accurate operation of the user's electricity information collection.
2 Comparison of different data transmission technologies
In the early stage, some provincial companies have piloted the construction of user power information collection systems. Among them, the remote channels in the data communication system mainly use GPRS / CDMA and 230 MHz private network methods. These two methods ensure the reliability of system communication and meet real-time There are some problems in terms of sexual and safety requirements. The GPRS / CDMA method needs to use the operator's resources to carry the user's electricity information on the operator's network. There are certain security risks. At the same time, due to the reliability and real-time performance of the user's electricity information due to GPRS / CDMA and 230 MHz There are also problems in this aspect. Therefore, for the user's electricity information collection system, it is necessary to select a remote channel that is safe and reliable and can ensure the real-time transmission of the user's electricity information data. Compared with the first two methods, fiber optic networking is more suitable in terms of ensuring system communication reliability, or meeting real-time and safety requirements. Since users are at the very end of the power grid, point-to-point fiber optic coverage should be used in an all-round way. The cost is too high. In order to save investment, it is very suitable to use EPON technology as the remote transmission communication of the user's electricity information collection system.
3 Introduction to EPON Technology
At present, the practical technologies based on PON (passive optical network) are mainly APON / BPON, GPON, EPON, WDM PON, etc. The main difference is that different layer 2 technologies are used. In order to better adapt to IP services, the 1st Mile Ethernet Alliance (EFMA) proposed EPON technology to replace ATM with Ethernet at Layer 2 in early 2001. The IEEE 802.3ah working group standardized it and can support 1.25 Gbit / s Symmetrical rate. With the further maturity of optical devices, IEEE will launch the IEEE 802.3av 10 G EPON standard in September 2009. The rate can be increased to 10 Gbit / s and is compatible with 1.25 G EPON. Because it perfectly combines Ethernet technology and PON technology, it is very suitable for the broadband access technology of IP services.
EPON transmits Ethernet packets through a point-to-multipoint, single-fiber bidirectional PON network. The EPON link layer uses Ethernet technology, so there is no additional overhead in packet encapsulation. The main purpose of EPON is to make full use of the advantages of PON and realize the function of a distributed Ethernet switch. EPON is composed of three parts: the central office equipment OLT (optical line terminal), the terminal equipment ONU (optical network unit) and the optical distribution network (ODN) composed of optical splitters and optical fibers; it can be considered that OLT and ONU form a distribution Ethernet switch. The splitter does not need a power supply, it is a glass body, and the input light can be divided into multiple lights of different proportions according to needs, such as 1: 2, 1: 4, 1:32, etc. This passive point-to-multipoint distribution structure constitutes The main advantages of PON.
EPON uses G.652 standard single-mode fiber with a downstream wavelength of 1 490 nm and an upstream wavelength of 1 310 nm; the link layer rate is 1.25 Gbit / s for the upstream and downstream symmetry; the length of the fiber in the PON network is 0.5 to 20 km .
The main standard of EPON is stipulated by IEEE802.3ah-2004. Operators (such as Japan ’s NTT and China Telecom) have made supplementary provisions in message encryption, OAM, and DBA, and have realized the interworking of EPON equipment.
EPON inherits all the characteristics of Ethernet, and can use Ethernet-based VLAN technology, packet encapsulation and forwarding technology, access authentication technology, DiffServ, queue management (PQ / WFQ), congestion control WRED and other technologies to flexibly implement all IP Broadband access, providing access security and QoS guarantee. Its unique DBA and OAM implementation enhances user bandwidth control and manageability.
4 Construction scheme of EPON system of power collection system
4.1 EPON technology is suitable for power collection system applications
The access points of the power system are scattered, the field environment is complex, and the expansion of the access points changes greatly. The construction of the copying and distribution automation network requires a set of advanced, stable and reliable communication extension systems with the best cost. As an all-IP broadband optical fiber access system, EPON can have a variety of networking methods such as star, F, and one-line, which can meet the needs of power system access. The application model of EPON power information collection system is shown in the figure. 1 shown.
Figure 1 Application model of EPON power information collection system
The passive optical network can work well in the wild environment, and has natural immunity to disturbances such as lightning and electromagnetic waves; the OLT is placed in the machine room of the high-voltage substation, and the optical cable is laid along the substation. Examples of bus-type optical fiber access solutions for each substation are shown in Figure 2.
Figure 2 Example of bus-type fiber access solution
When adding substations, the branch optical path can be led from the splitter to access without additional equipment; for an access environment with high reliability requirements, a hand-in-hand network can be used to achieve full optical path protection, as shown in Figure 3.
Figure 3 All-fiber protection networking of "hand in hand" structure
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