Preliminary Study on Remote Automatic Meter Reading System in Rural Power Grid

Today, with the rapid development of science and technology, county-level power companies are still using the most primitive methods of human meter reading, carrying ladders, riding motorcycles and taking village streets to read meters, regardless of wind, rain or cold One day. Meter reading is currently the most costly task for county-level power companies. In particular, as the size of rural power grids expands, the number of users increases rapidly. Manpower meter reading workloads are inefficient, man-made errors are severe, and missed copying. The phenomenon of misappraisal, copying, and copying occur from time to time, which is detrimental to the timely and full collection of scientific management and electricity charges, and also has a certain impact on quality service work. In recent years, remote automatic meter reading technology has developed very rapidly. There are examples of applications in urban residential communities. However, compared with the rural grid where the urban power grid is dispersed and the grid structure is weak, the application of remote automatic meter reading technology is relatively rare.

1 Remote automatic meter reading system communication method Remote automatic meter reading system is a collection of electricity meter data acquisition, carrier transmission, data storage, data communications, data processing and power control and other functions in one automated system. One of the major technical difficulties existing in remote automatic meter reading technology is communication technology. Communication equipment occupies most of the investment in meter reading systems, and the reliability of communications has a decisive influence on the reliability of the meter reading system. Choosing a suitable communication method can greatly improve the reliability and practicality of the system, so that the system can be widely promoted. At present, the most common forms of communication for remote meter reading systems at home and abroad are the following.

1.1 Dedicated Wired Communication Line Modes This type of communication scheme is generally used for bus communication and mainly includes: RS485/422 bus. This is a widely used method of the bottom layer communication of the automatic meter reading system. It is generally used for communication between each meter to a centralized meter reading device, and the physical medium is a twisted pair cable. The anti-interference ability of the twisted pair is strong, the channel is stable, and the communication speed and the communication distance can well meet the requirements of the bottom communication of the automatic meter reading system of the urban residential community. However, RS485/422 only provides physical layer specifications, and the software development workload during product development is detrimental to the standardization of products.

ProfiBus, BitBus, CAN, LnoWorks and other field buses. Its physical layer is the same as RS485/RS422, but it has added protocol support at the data link layer or higher layer to deliver data in the form of information packets. Its internal software modules complete tasks such as data packetization/decompression packets and CRC check. This type of standardized field bus has mature technology and small secondary development workload. Most products adopt error control technology at the data link layer and the transmission layer, which greatly improves the reliability of communications. However, the dedicated wired communication method has a large amount of wiring work, and the communication channel is subject to human damage. After the damage is eliminated, the difficulty is eliminated and the recovery is slow. Generally, this method is only applicable to close-range communication.

1.2 Telephone Line Communication Mode The telephone line communication mode is mainly used for remote data transmission after centralized meter reading, and more applications are in the process of communication between the concentrator and the meter reading management center. At present, most of the data concentrators and management centers are equipped with an external modem (MODEM) or a built-in MODEM chip solution. The communication rate can reach 2.4 kbps, 9.6 kbps, or even 56 kbps. The host's call to the concentrator can be done automatically by dialing the switch, or it can lease the leased line, but the cost is high. When data communication is performed by the telephone line method, the line connection (including call answering, etc.) takes a long time and usually takes several seconds to several tens of seconds. This aspect makes the management center can not be real-time monitoring of users; on the other hand when a large number of terminals, leased telephone lines and more, its rental costs are very substantial, and therefore not suitable for large-capacity systems.

1.3 Dedicated wireless communication methods Wireless methods mainly include radio communication and infrared communication, which are relatively mature conventional technologies. This manner has greater flexibility in terms of transmission bandwidth, communication rate, communication distance, installation, etc., when the communication between the terminal layout of the dispersion is a better choice. Its main disadvantage is that it needs to apply for frequency usage rights. If the frequency selection is unreasonable, adjacent two channels will interfere with each other. Its use occasions have certain limitations.

With relay transmission and automatic networking as technical features, wireless ad hoc network technology has developed rapidly in recent years. For example, Zigbee network technology, which is mainly used for near-field communication between sensors, can be applied to bottom-level communication in automatic meter reading systems due to its features of low cost, automatic networking, and the like. Especially when the users are relatively concentrated, the data of each meter can be transmitted to the concentrator by means of micro power transmission, relay transmission, and adaptive routing.

1.4 low-voltage power line carrier communication system is a power line carrier communication means as the use of existing low-voltage 220V line communication bearer, by way of the carrier signal is digital or analog transmission technology. The technology does not need to lay the communication line any more, the construction quantity is less, the capital investment is saved, and it is beneficial to management, and the channel is not easy to destroy.

In the automatic meter reading system, a method of centralizing the data of multiple users after being transmitted is generally used to avoid waste of communication resources and increase of cost. However, rural residents live in a decentralized manner, and each power meter accounts for a long distance between concentrators. It is difficult to use a wired communication method such as twisted-pair cable for the underlying communication. On the other hand, the rural power supply network has few branches and is suitable for power line carrier communication. Therefore, power line carrier communication has certain advantages in the automatic meter reading system of the rural power grid.

1.5 GPRS/SMS communication method based on mobile phone network GPRS/SMS communication is attached to GSM mobile phone network, and the data rate of GPRS can reach 115kbps. The data rate of short message communication can reach 9.6kbps.

GPRS allows service users to send and receive data in the end-to-end packet transfer mode. It does not require the use of circuit-switched network resources and charges according to data traffic. Therefore, it is suitable for intermittent and non-periodic data transmission; frequent transmission of small amounts of data. ; Infrequent transmission of larger capacity data. Short message communication is suitable for occasions with low data volume and low real-time requirements.

At present, mobile phone networks have basically achieved full coverage of residential areas, service quality has increased year by year, and tariffs have been gradually reduced, while automatic meter reading systems have the characteristics of small data volume and low real-time requirements, so GPRS/SMS communication is Automatic meter reading system has a good application prospects.

2 The structural characteristics of rural end-use power grids Wuyi County is located in the middle and large plains of Langzhong. The houses in rural areas are relatively concentrated in the mountainous areas, but are slightly scattered relative to the cities. There are main streets in the north-south and east-west directions of the village, and there are two adjacent villages. The distance is generally within 5 kilometers. The lighting transformer is generally one for each village, and the larger village has 2-3 sets. The capacity of each lighting transformer is mostly 30 kVA and 50 kVA. The low-voltage outlet is decided according to the position of the transformer, and the transformer is in the middle of the village. 2 generally has a low pressure return line (three phase four wire), to try to ensure balanced three-phase load, carried by each phase line is about one-sixth the number of households in the village households; village a transformer mounting position In general, the low pressure is a return line (three-phase four-wire). The number of households on each phase line is about one-third of the total number of households in the whole village, and the smaller ones are usually dozens of households and one hundred. Multi-family, the larger village can reach several hundred households. The distance between two neighboring rural households is not much different from that of the bungalows in the cities, and they are generally in the tens of meters and hundreds meters. The table of the household is fixed on the outdoor wall with a set table box. According to the number of households in each area (hutongs), different types of set boxes are used. The number of electric meters (standard external dimensions) installed in each set is generally Divided into 4 blocks, 6 blocks and 8 blocks.

3 Long-distance automatic meter reading system of rural power grids According to the structural characteristics of rural power grids, it is more appropriate to design the remote automatic meter reading system as a four-layer structure, ie meter reading management center, power relay data relay and management substation, village-level data. Concentrator, carrier set copy meter.

The meter reading management center communicates with each power supply station through the existing fiber channel, and is responsible for collecting, collating, and processing the user's power information transmitted from the remote meter reading terminal, and provides it to the charging system and the power consumption management system. The meter reading management center also manages the concentrators in the jurisdiction through the host computer management system, and sets and maintains the concentrator and the carrier meter differently.

According to the system scale and management system, a county-level power supply company can establish one or more meter reading management centers. Each management center can be connected through a communication network within the power system.

The meter reading management center is composed of the meter reading management computer and the upper computer meter reading management system software, and is a part of the direct communication between the meter reading manager and the system. The upper computer management system is located on the computer of the meter reading management center. It is actually a set of software management system based on the database. The meter reading management center and the power supply station are in a 1:N relationship. A meter reading management center is responsible for managing multiple power supply stations under the area.

3.2 Data Relay and Management Substations of Power Supply Bureaus The power supply/substations (all in one station mode) of the Wushu Bureau have opened optical cable communication with the bureaus, so long as the data collected by the concentrators is sent to the power supply. The institute can be uploaded to the county bureau meter reading management center by centralized power supply. The power supply station and the 35kV substation are combined into one station, and each village's lighting transformer is directly connected to the 10kV power line, and the conditions for carrier communication are fulfilled. Therefore, the data from the village-level data concentrator is uploaded to the substation (power supply station) via 10 kilovolt carrier communication, and the model uploaded to the county meter reading management center by the power supply station using the existing microcomputer network is more economical and practical.

The data relay and meter reading management center of the power supply station is mainly composed of a carrier communication machine, optical fiber communication equipment (existing) and a power supply management computer (existing), and mainly completes the data processing functions of data relay and power supply areas. Because the power supply can monitor the power consumption of each user in real time, on the basis of automatic meter reading, it can also increase anti-theft power, security monitoring and other functions. This has an important role in increasing the safe and economical operation of the power grid.

3.3 Data concentrator The data concentrator, which is connected to the high voltage and low voltage sides of the village-level low-voltage distribution transformer, is the most important data acquisition terminal equipment. It communicates with the 10kV power line carrier channel, fiber channel, power supply station, and meter reading management center, receives commands from the power supply and management center, and automatically completes meter data transcription. Downstream through the low-voltage power line carrier communication mode, collect the data (basic functions) of all carrier electricity meters and village-level power distribution meters under the distribution transformer, and send user stop and power transmission and distribution instructions to the collection terminal according to the instructions to complete the user's Remote split and closing control (optional function).

3.4 Carrier wattage meter The carrier watthour meter is installed in the meter box and completes the collection of all user meters (1-8) installed in the same meter box. And upload the received data to the concentrator. The carrier electricity meter collects data mainly through the secondary processing of the data of the user's electricity meter. This not only can avoid a large amount of electricity meter replacement and result in a waste of customer investment, but also allows the remote automatic copying data to be mutually verified with the existing meter data. The reliability of the data.