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Application of CAN bus in substation high-voltage switchgear detection system

Abstract: in view of the shortcomings of the monitoring network system based on BITBUS bus and RS-485 bus used in most substations in China, this paper introduces a high-voltage switchgear detection system using CAN bus, which can better improve the function of substation monitoring system, puts forward the design scheme and implementation of its main hardware and software, and introduces the application effect

key words: detection system can bus fieldbus due to the progress of electronic information technology, fieldbus technology has been widely used in the function intelligent system of high-voltage switchgear, which makes the detection system of high-voltage switchgear form a distributed monitoring system, and makes the whole system more powerful and more perfect than the traditional centralized monitoring system

1 can bus technology and its characteristics

in the traditional substation monitoring system, after completion, BITBUS and RS-485 bus will generally be adopted based on the advantages of rare earth resources in Fujian Province and the existing rare earth industry foundation in Xiamen, but they have the following defects in practical application:

a. bitbu has the practical application value. S bus and RS-485 bus can only have one master node, which cannot form a multi master system. Once the master node fails, The system cannot operate normally, resulting in poor reliability of the whole system

b. the anti-interference ability of BITBUS and RS-485 bus is poor, which is not suitable for operation in high electromagnetic environment, and their error handling ability is also very poor

c. the data communication mode is command response, and the lower node can respond only after receiving the command from the main node, so that the data cannot be uploaded in time, resulting in poor real-time performance of the whole system, which is not suitable for the system with high real-time requirements such as switchgear detection

this paper adopts the controller area network can, which is commonly used in industrial measurement and control systems at present. The CAN bus adopts differential drive, which can be applied to the environment with high noise interference and has strong error correction ability. At present, the international standard iso11898 specification has been formed [1]. With low price, high reliability and flexible structure, it is one of the most promising fieldbus

can adopts two of the seven layers of osi/iso model, namely physical layer and data link layer. Users can develop corresponding application layer communication protocol according to actual needs based on these two layers [1]. The main features of can are as follows:

A. It can work in a multi host mode. Any node on the network can actively send information to other nodes on the bus at any time, so it can form a multi host system

b. when canadidas - energy boost node is seriously wrong, it has the function of automatically turning off the output, cutting off the connection between the node and the bus, so that other nodes on the bus and communication will not be affected, so it has strong anti-interference ability

c. non destructive bus arbitration technology is adopted. When two nodes send information to the bus at the same time, the node with low priority actively stops sending data, while the node with high priority can continue to transmit data unaffected, saving bus conflict arbitration time and avoiding bus conflict

d. the node information on the bus can be divided into different priorities to meet different real-time requirements

e. data can be sent and received in several ways, such as point-to-point, point to multipoint and global broadcasting

f. the direct communication distance of can can can reach 10km at most, and the transmission rate can only reach 5kbit/s at this time; The maximum communication rate can reach 1mbit/s, and the maximum transmission distance is 40m at this time; The number of nodes on can can can actually reach 110

g. can adopts a short frame structure, each frame of information contains 8 bytes, and has CRC verification and other error detection measures. The transmission time is short, ensuring a low data error rate

h. the communication medium adopts twisted pair, coaxial cable or optical fiber, which can be selected flexibly

in a word, the CAN bus has strong real-time performance, high reliability and simple user interface, which is very suitable for the fault detection system of high-voltage switchgear in substations

2 overall design scheme of the system

the structure of the detection system of high voltage switchgear is shown in Figure 1

the whole system connects each acquisition unit module and monitoring computer unit into a distributed field control network through CAN bus. The computer and each detection unit module in the network have their own ID marks, and ensure that their IDs are not repeated. The data acquisition unit module collects various signal parameters of the switch cabinet and sends them to the system monitoring unit through the CAN bus to establish the database of the high-voltage switch cabinet of the whole substation. The computer monitors and manages the whole can bus system, and has the functions of system parameter (such as transmission rate, node address, etc.) setting, data sending, data receiving, local state inquiry, node state inquiry, interrupt state inquiry, etc. The system monitoring machine unit is composed of industrial control machine and can bus communication interface card. It receives the data sent by the data acquisition unit module, and obtains the values of various parameters of the high-voltage switchgear through corresponding calculation and processing by the computer. According to the correlation quality of various parameters and their waveforms, the working state of the high-voltage switchgear is analyzed in detail. The CAN bus communication interface card makes the industrial control function conveniently connected to the CAN bus. It is composed of the can interface circuit and its connection circuit with the computer serial port to ensure that the data can flow accurately between the CAN bus and the computer

3 hardware circuit design

since the computer serial port is a standard RS-232 interface, the data signal sent is transmitted in bytes, while the an bus signal of C such as pressure testing machine, tension testing machine, universal testing machine, etc. is transmitted in frames, so if you want to transmit data between the computer serial port and can bus, you must have a CAN bus communication interface card, The function of this card is to convert the format of the signal sent by the computer serial port and the signal sent by the CAN bus, so that each party can recognize the signal sent by the other party and realize data flow

the hardware circuit design of the CAN bus communication interface card in this paper is shown in Figure 2, in which the oscillation circuit and reset circuit are omitted