1 Introduction
With the rapid development of Internet technology and its widespread application in various industries, a remote monitoring system is developed to monitor and control the operating safety parameters of power equipment in real time and automatically alarm for sudden events on site, so as to realize the safety protection of the substation environment and the visualization management of necessary production equipment [1].
With the rapid development of the power system and the increasing requirements for intelligent software functions and performance, the limitations of the traditional C/S mode management information network have gradually become apparent. Against the backdrop of the rapid development of network technology, the B/S mode monitoring system can solve a variety of problems faced by the C/S system development method in the increasingly complex heterogeneous network distributed environment [2].
2. Overall System Structure
The overall system structure is shown in Figure 1. The communication front-end unit serves as the data front-end for the host computer. All data from the lower-level computers is transmitted to the communication front-end unit in the form of data frames via an RS485 bus, following standard Modbus, IEC101, IEC103, and system-defined protocols. Given the widespread application of network technology, the system supports Ethernet communication and employs TCP/IP-based Socket technology. After decoding, the data is transmitted via WCF communication services distributed across different servers to real-time, historical, and file databases, providing access to the web server. The communication front-end unit supports various RTUs, intelligent meters, intelligent modules, and even PLCs with standard protocols, making the monitoring system highly versatile and portable.
The client runs in a browser with the Silverlight plugin installed. It sends a request to the web server, which responds to the request and then sends the data to the browser in HTML format, where it is displayed in a user-friendly interface.
Figure 1 System Overall Structure
3 configuration server
3.1 Unit Configuration
In a system, unit configuration means simulating the physical RTU device. Lower-level devices come in various types and series, such as line protection devices, transformer protection devices, and generator protection devices. The configured unit corresponds to this, including the device's parameter information, data information, and communication address. Configuration establishes the connection between the monitoring system and the device.
3.2 Image Configuration
The image configuration section is associated with the unit configuration; it draws images for the monitoring screen module based on the configured units. Different configured units contain their own specific electrical components; this module includes 50 graphic elements. It draws and saves information models of the electrical characteristics of distribution networks according to the IEC 61970 standard. This improves the system's compatibility with other power industry monitoring systems.
4 System Design and Function Implementation
Power monitoring systems have high requirements for real-time performance and security. They not only require a user-friendly and flexible monitoring interface, but also real-time, stable, and secure communication. Based on these performance requirements, the system is mainly designed with the following eight functions: real-time data retrieval (completed on the communication front-end unit), database, real-time data display (monitoring screen), web-based reports, fault filtering, event alarm management, setpoint modification, and communication message monitoring. These functions are primarily designed around three main aspects: on-site data retrieval, monitoring and data analysis, and remote control.
4.1 Password and Access Control
Based on the security requirements of the power monitoring system, the access control system design combines passwords, permissions, and levels, issuing different levels to users and granting corresponding permissions. Customers need to enter a password to enter the system and pass verification before gaining access. For critical operations such as sending remote control commands or configuring images, verification of a correct password, reaching a certain level, and possessing the corresponding permissions are mandatory before the operation can be performed.
4.2 Communication front-end processor
The system decodes data from remote acquisition devices, performs preliminary data processing, and provides a WCF interface to load the data source and transmit it to the monitoring system's data center, according to system design requirements. The communication front-end will connect to multiple RTUs, resulting in frequent and large-volume data exchange. Based on extensive testing, the system selected the more stable and reliable thread pool technology between polling for serial port data reading and using a thread pool.
4.3 Monitoring screen
The real-time data display is presented to the user, and the system must be user-friendly, intuitive, and visually appealing. Displaying the data means showing the status of actual devices such as vacuum contactors, circuit breakers, and disconnectors in the field to the user. Based on the information model of the electrical characteristics of the IEC 61970 power distribution network, the system uses an image configuration module to configure specific electrical component graphics, which, when connected to real-time data, completes the monitoring of the field's operational status.
4.4 Fault Filtering and Communication Message Monitoring
Both fault filtering and communication messages provide engineers with the basis for analyzing data. The former records and analyzes faults that occur in the power grid, while the latter monitors the communication status of the communication front-end and RTU devices in real time.
4.5 Event Alarm Management
The system automatically displays alarm status information detected by the device and records all generated operation information, prompts, and alarm messages. Different alarm sounds are played based on the type of alarm event. Additionally, TTS (Text-to-Speech) technology allows for the option of broadcasting alarm information verbally.
4.6 Fixed value modification
Remote control commands and device parameter settings are achieved by modifying set values to control the opening and closing status of disconnectors in the power station and to retrieve data information.
5 Database Module
The key module of the database monitoring system is also the design difficulty. It is located at the hub of each functional module. The database distribution is shown in Figure 2. The system integrates traditional file storage, database storage and memory storage, namely file data, historical database (MySQL) and real-time database. The real-time database is a class (DataManager). All data transmitted by the communication front-end machine is first initialized and loaded into this class. Historical database and file storage data are also obtained through this class. MySQL database provides APIs for various programming languages, optimized SQL query algorithms, multi-threading technology and open source code, so the system selects it as the data storage medium [3].
The data used in the monitoring screen comes from a real-time database, which is continuously refreshed on a timed basis. This data is directly used as the data source for real-time curves, bar charts, and on/off statuses on the screen. However, fault information and small amounts of data that need to be stored long-term are saved to files in real time; this data is not shared. For large amounts of collected data that need to be shared, a MySQL database is used. By combining these data storage methods, the database not only ensures sharing and integrity but also reduces system memory load and speeds up system response.
A logic layer was added between the database layer and the interaction layer to completely separate them. The logic layer is responsible for data querying and storage, directly manipulating the database downwards and transmitting data upwards via WCF services. This approach is primarily to ensure the independence of the interface layer and the underlying data. Using WCF as an intermediary ensures that changes to both ends will not affect each other, as long as the publicly exposed interface remains unchanged, laying a solid foundation for future system upgrades and maintenance.
Figure 2 Database Distribution
5.1 Historical Data Reports
The structure and distribution of the database have been introduced above. Historical data reports extract historical data from MySQL. Based on the device's hourly meter readings and cumulative data on current, voltage, power, and energy, as well as the equipment's operating conditions, time statistics, and technical statistics such as pass rate and load rate, RDLC reports can be dynamically designed by combining conditions such as accident, measurement, metering reports, time-sharing reports, shift reports, daily reports, monthly reports, and annual reports. Finally, the service is requested from the logic layer. The returned data is filled into the report [4]. RDLC reports provide rich functions, such as drill-down and printing functions, which meet the power industry's need for frequent data printing and drill-down of intuitive curves and bar charts.
5.2 Variable Group Data Report
The data source for variable group data reports is a file database. Queries can be performed based on custom time intervals, maximum values, minimum values, real-time values, average values, and other criteria. This type of report is a screen report module displayed on the monitoring screen, showing data in four ways: variable, variable group, variable curve, and variable bar chart.
6 key technologies achieved
6.1 Introduction to Key Technologies
In a monitoring system using the B/S model, real-time updates of the status of elements and alarm information in the monitoring screen require the client to send a request to the server, and the server to respond and send the response back to the client via static text. Automatic alarm information is easily achieved in the traditional C/S model. To provide users with a user-friendly and intuitive human-computer interaction experience, the system uses Microsoft's Silverlight technology, which is a cross-browser and cross-platform technology that can design, develop and publish web interactive programs with multimedia experience and rich interface application (RIA) [5].
The data connection of each module in the system adopts WCF technology, which is an SDK for developing and deploying services on the Windows platform. It provides a runtime environment for services, enabling developers to expose CLR types as services and use services in the manner of CLR types [6]. In the system, the data communication of each module is connected by WCF, which makes the distribution between modules independent. The monitoring screen uses the combination of Silverlight and WCF technology to push server data to the web page, realizing the dynamic display of data. In addition, multi-threading technology is used in the data refresh and interface display, which greatly reduces the CPU usage.
6.2 Application of Key Technologies
6.2.1 Real-time data connection
Connecting real-time data to the monitoring screen is an example of the combined application of multithreading and WCF technology mentioned above. Real-time data includes SOE quantities, operational quantities, analog quantities, digital quantities, and accumulated quantities, all originating from the communication front-end server. There are two ways to obtain data through services. One method is through proactive web page queries, where the Silverlight client actively requests data from the communication service to update the real-time database (DataManager) via a timer. The second method uses a communication server push, with the client passively receiving data; that is, the server receives data from the RTU and pushes it to the client via a WCF callback. Each method has its advantages: the former reduces the client's workload but increases the communication server's, while the latter is the opposite. From the system's perspective, the second method is preferred because a large number of data connections can affect the response speed of the human-machine interface. However, considering the development of the power industry, the functionality of the communication front-end server should be minimized, as the monitoring environment is sometimes harsh, making it impractical to deploy a computer on-site. Therefore, the system chose the latter method based on the actual situation.
To address the issue of UI being affected by data refresh, multithreading technology was applied to the system. Multithreading in Silverlight is essentially consistent with other threading technologies. Calling WCF in Silverlight is asynchronous; a dedicated project was created to handle the query service. The monitoring module subscribes to the query completion event and calls this project. The project starts a new thread, first retrieving the data type to be queried from the configuration server, then querying each type in a loop. Because WCF services are asynchronous, a conventional loop approach cannot be used; instead, a circular approach is employed, triggering the next query only after the asynchronous completion event. In the monitoring interface logic, a timer is used for periodic queries, with a system timer period set to 1 second. Based on the image configuration elements and connection data information, the corresponding data information is retrieved from the real-time database.
6.2.2 Monitoring screen drawing
Silverlight enables the development of web applications with professional graphics, audio, and video capabilities, enhancing the user experience. The system primarily utilizes basic graphics functions; it's a lightweight client-side vector drawing tool. Graphics drawing is divided into two parts: first, image configuration using custom controls in Silverlight, which contain information such as the size, position, color, and status of the elements. This combines each element's control into a component library, allowing drawing to occur by passing in the corresponding data during configuration. Second, monitoring the screen, such as using animation effects to simulate status light blinking. Creating animation effects using Expression Studio simplifies the process and enhances the results.
Primitives are embedded into the image using multiple Canvases. The entire image is a large canvas, and each primitive is drawn using a smaller canvas, which is then embedded into the large canvas. During data refresh, each primitive can be selectively refreshed based on its own attributes without affecting the refresh of other primitives.
7. System Requirements and Deployment
System requirements:
Operating System: Windows XP SP3, .NET Framework 3.5
Web server: IIS 5.1
Database: MySQL 5.9
Development environment and tools: Microsoft Visual Studio 2010, Silverlight 4, WCF, ASP.NET.
Client-side requirements: IE 6.0 and above, Firefox and other mainstream browsers, Silverlight 4 web browser plugin.
System Deployment:
Web Server: For hosting web pages, the system chose IIS. IIS is a commonly used web server software, known for its ease of use, simple operation, and stable performance. Deploying IIS is a crucial and complex process. Websites involve virtual directories, website creation, and other operations. Directly creating a web installer, with numerous configuration changes required, becomes quite tedious. Therefore, we created an automatic IIS installation program, including the following main steps: software environment detection (different systems use different IIS versions), Web.config modification, website creation (file decompression -> website creation -> website browsing), and IIS additional functions (viewing sites, starting sites, stopping sites, restarting IIS, stopping IIS, and starting IIS).
For database security reasons, it must be deployed on a separate computer. The communication front-end server and WCF server are deployed together, while the web server runs independently. Running the deployment package described above will allow the system to function normally.
8. Summary
This system is a web-based power monitoring system built on the .NET platform, utilizing cutting-edge technologies such as WCF and Silverlight, which are heavily promoted by Microsoft. The system can monitor, analyze, and remotely control the operational quality of power systems in real time, effectively, and intuitively via LAN or even WAN. Only a Silverlight plugin is required on the client side. The system boasts advantages such as simple server maintenance and reliable performance. Having passed the pre-release testing phase, the system is now officially deployed in substation projects, providing substation staff with effective support for analyzing power system faults and remote control. Due to limitations in network technology, the system is slightly slower than a client/server (C/S) model; we hope everyone will work together to improve its performance.
References
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[3] George Reese, Randy Jay Yarger, Tim King & Hugh E. Williams. Translated by Lin Qi, Zhu Tao, and Jiang. MySQL: The Definitive Guide [M]. China Electric Power Press, 2003.5
[4] Shang Debin, Liu Guilan, Integrated Automation System for 110kV Substations [J]. Electrical Age, No. 8, 2004
[5] Ding Shifeng. Mastering Silverlight-RIA Development Technology Explained [M]. Posts & Telecom Press, 2008.6
[6] Juval Lowy, author; translated by Zhang Yi and Xu Ning [M]. Beijing: China Machine Press, October 2009.
