The temperature monitoring system scheme of switch cabinet based on wireless sensor network
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I. Overview
When the switch cabinet is running for a long time, there is no special ventilation method in the cabinet, especially in summer, the temperature in the cabinet is high, and there is no temperature measurement measure at present, so the substation staff does not know the temperature in the cabinet and adopts blind operation Therefore, possible problems cannot be found and resolved immediately.
The traditional detection method is to send temperature information to the monitoring center through a serial bus such as RS232 or RS485, and the monitoring center makes processing decisions. Although this method is simple, the serial bus transmission method is affected by factors such as serial lines, and the transmission distance is limited; and long-distance wiring is required, which makes repairs and maintenance difficult. Based on the wireless sensor network, using mature wireless transmission technology, while maintaining the reliability of the system, the advanced nature of the system is guaranteed. There is no need for long-distance complicated wiring, each wireless local area network module can be installed flexibly, and there is no need to re-wiring when changing the installation position; at the same time, because there is no need for wiring of other lines except power cables, it is safer and more reliable. In addition, after connecting multiple cable connectors into a network, it is convenient for unified management and realizes networked and automated management.
2. Switchgear temperature monitoring system based on wireless sensor network
2.1, system overview
The design goal of this system is divided into three steps. First, design the terminal collection equipment of the wireless sensor network, including the selection of temperature sensor and the realization of the collection circuit and processing algorithm; then design the installation of the wireless sensor terminal equipment according to the characteristics of the substation; finally, through the wireless sensor network Optimize and apply it to power cable joint fault monitoring, making the cable fault monitoring automatic, wireless, networked and safe.
2.2. System composition
The system consists of a temperature sensor, a temperature inspection instrument, a wireless transmission device, a wireless monitoring server (receiving device) and its management software. The wireless temperature measurement system adopting the networking technology of the emerging wireless sensor network realizes real-time online detection of the temperature of the switch cabinet of the substation. After connecting with the power automation system, the operation status can be monitored in the central monitoring room, which is truly remote In remote measurement, when the temperature of the measured point exceeds a preset threshold, an alarm signal will be issued to remind the relevant personnel to take measures in time.
2.3 System characteristics
The system has real-time online monitoring, and the accuracy of measurement accuracy can reach ±0.5℃; users can set the flexibility of parameters according to their own needs; whether it is products, tools, and maintenance, it has system security and reliability; realizes wireless Automatic networking among equipment forms a MESH network topology; it realizes the functions and characteristics of temperature timing collection mode.
2.4. Introduction to system function modules
Sensor part
Temperature probe: Cu50 thermal resistance with a metal shell protective sleeve, measuring range -20℃-+100℃, accuracy ±0.2℃. Due to the addition of a metal protective cover, on the one hand, it can protect the temperature probe during installation; on the other hand, since metal has good thermal conductivity, it can conduct heat.
Wireless network terminal equipment
The wireless network terminal equipment is the core of this system, responsible for the temperature data collection and transmission of this system. This system is equipped with temperature sensor interface to realize over-temperature alarm. When the wireless network terminal equipment removes the temperature detection function and configures the corresponding software system, it can become a wireless relay contact and wireless control terminal, so wireless network terminal equipment (temperature measurement), wireless relay contact, wireless control terminal equipment hardware It is universal.
Reference drawing of wireless network terminal appearance
③Temperature inspection instrument
The temperature inspection instrument is responsible for collecting the temperature and sending the temperature value through RS485 transmission. The inspection instrument has rich interfaces and can adapt to various industrial environment alarms or other alarm requirements. The panel has four LED displays. The temperature sensor can be configured to realize sound and light alarms such as power failure and over temperature, and over temperature alarm calls to start the air-conditioning system. Abundant control methods: photoelectric isolation mode 2 relay outputs ITU (normally open type); flexible and concise setting mode: 3 keys, namely function keys, plus 1 and minus 1 keys, used to set the upper and lower limits of temperature and humidity.
Reference diagram of temperature patrol instrument
④Remote data transmission
Wireless network interface data transmission: Due to the use of the latest 2.4G wireless communication method, the communication distance can reach 100m, and the transmission distance can be increased to hundreds of meters or even farther through wireless network routing; Ethernet mode data transmission. In a computer room with an Ethernet interface, the temperature collected from the wireless network can be published through the Web through the 10M/100M network port.
⑤ Anti-emergency handling
An emergency button can be installed inside the computer room. In the event of an emergency, an alarm device can be manually activated to notify the monitoring center.
⑥Equipment of the control center
The control center equipment provides two options:
The first solution: configure a PC, and develop graphical software and Web service software on Windows.
Real-time monitoring of continuous changes in the field temperature, displayed in the form of a graph or histogram
This kind of scheme has many advantages: realize the storage and management of temperature data. It can realize historical data query, and print reports according to query results and styles; when the temperature exceeds the specified value, an alarm message will be issued to prompt the operator to check whether the substation is malfunctioning; the temperature curve and temperature report of the system can be published through the Web, and remote users can Query the temperature history record through the browser; the system application software adopts plug-in or embedded (with interface) design, the software is easy to install, simple to operate, complete functions, and convenient to maintain. Under the condition of data communication with the computer room, the manager can remotely set the alarm value of each environmental sensor and define different levels of alarm methods. If there is an abnormality, the management staff can be notified in time by means such as sound. When an alarm occurs, the alarm item in the software is displayed in red.
The second solution: use the embedded Web server solution
Traditional Web servers use workstations or PCs with high computing power and mass storage capacity as hardware working platforms, and non-real-time operating systems as software working platforms. Large and complex server programs run on them, typically based on Windows NT. IIS (Internet Information Server), Unix-based Apache Web Server, etc. Although the function is powerful, but at the same time, because the software and hardware platform of the equipment is too large and complicated, it needs to be maintained by special personnel, which also limits its wide use. The emergence of embedded Web server based on embedded technology has opened up a brand-new way to solve the above problems.
The web server of this scheme uses a 32-bit embedded processor as the hardware work platform, an embedded multitasking operating system (linux) as the software work platform, and is equipped with technologies such as dynamic web pages and CGI to run a small and streamlined server on the embedded server. program. For remote users, there is almost no difference between accessing an embedded Web server and accessing a large-scale server. The embedded server has the advantages of miniaturization, specific and stable equipment functions, etc., which can be used as an alternative to the Web server.
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