Abstract: Combining PDA, computer and wireless communication technologies, and using Delphi and EVC development tools, a smart system for on-site verification and management of electricity meters was designed and developed based on a relational database developed with Oracle 8i. This system enables paperless operation and intelligent management of electricity meter calibration.
Keywords: electricity meter; on-site verification; PDA; GPRS; Oracle; expert diagnosis
With the development of the power industry, the number of electricity users is increasing. Timely and accurate calibration of electricity meters in operation is essential to ensure power safety and accurate electricity metering. In the past, meter calibrators would first assign their daily calibration tasks, then take the calibrators to the calibration site, record the calibration results in a notebook, and finally input the results into a computer. This process not only overwhelmed meter calibrators with scheduling, data recording, and report generation, but also carried the risk of errors at any time.
Based on the above reasons, an intelligent system for on-site verification and management of electricity meters was designed. This solution is based on PDA (Personal Digital Assistant) and GPRS (General Packet Radio Service) technologies. It uses the PDA to temporarily store data and transmits it wirelessly via the GPRS network, establishing a data communication link between the verification site and the main station server, thereby achieving paperless, automated, and intelligent on-site electricity meter verification. Simultaneously, the system includes powerful management software to manage meter data information, thereby achieving rationalization and systematization of the meter verification work.
1. System Composition and Workflow
The system mainly consists of three parts: the main station management software module, the main station database module, and the PDA field calibration module. The system architecture is shown in Figure 1.
The entire calibration process can be divided into:
• Plan Development. The plan generated by the main site software takes effect after being reviewed by the metrology specialist.
• Work assignment. The plan is distributed to each group by the head of each diplomatic platoon.
• Task Download. The calibration personnel download the calibration tasks to be performed to the PDA.
• On-site calibration. Calibration personnel bring a PDA and calibration instrument to the calibration site to perform calibration work. If any abnormalities are found on-site, the PDA's wireless communication function is used to connect to the expert diagnostic system of the main station to handle various wiring errors.
• Upload verification results. After the table calibration is completed, the calibration personnel can upload the verification results to the main station via wireless or serial communication.
• Compile various reports.
2 System Implementation
2.1 Design of the Main Site Management Software Module
The main station management software module adopts a C/S (Client/Server) mode with high security and stability, reads and writes the main station database, and realizes functions such as management of electricity meter information, arrangement of meter calibration work, processing of meter calibration data, diagnosis of on-site wiring errors, and statistics of various reports. The development of the main station management software uses the Delphi 6 development tool from Borland, which has the characteristics of visual development environment (IDE), fast compiler speed, powerful database support function, flexible VCL components, cross-platform development, etc., and is highly favored by application developers [2]. The various functional modules are shown in Figure 2.
Communication module. The GPRS front-end processor's data forwarding function is used for communication between the main station and the PDA, enabling wireless communication and significantly reducing external network attacks on the main station server. It also provides interfaces for marketing systems and expert diagnostic systems.
System management. The system allows you to set up departments and staff within each department, and assign appropriate menu permissions based on staff levels.
Record management. Operators can manage information such as departments, meters, substations, users, and areas, and can also query operation logs.
Task management. This includes generating planned tasks, downloading calibration tasks, and uploading calibration results.
Report management. Various reports and intuitive statistical charts are provided to meet the actual needs of the metrology institute.
2.2 Main Site Database Design
The main server is equipped with Oracle 8i database. Oracle database has the characteristics of strong security, good compatibility, high availability, high productivity, and multi-threaded processing capability. It is one of the most widely used relational data systems in the world [3]. The database belongs to the underlying shared data resource support layer in the whole system, and provides support for basic data storage, management, query and other functions for upper-layer applications. The database includes customer table, substation table, line table, meter table, measurement point table, task table, plan table, verification result table, etc. The simplified table structure design is shown in Figure 3.
2.3 Hardware and software design of the PDA calibration module
The PDA meter calibration module includes a calibrator and a PDA with a GPRS network card. The calibrator is used to calibrate and test the electricity meter, while the PDA is used to store the calibrator data and communicate with the main station.
The PDA calibration software is designed in accordance with the standard [4] and the actual calibration process. The software module provides an interface for manual input of intuitive inspection information, such as whether the meter casing is intact, whether the current range is normal, whether there is current loss, whether there is voltage loss, whether there is overload, etc.; it receives meter data through serial-to-infrared communication; it receives data from the calibrator (PWS) through the serial port. If it is a PWS with infrared, it can receive PWS data through the infrared port in front.
The PDA software provides two methods for data communication with the main station:
• GPRS communication method. The PDA communicates wirelessly with the main station's server at the testing site to query and retrieve information and upload results in real time. If there is any abnormality in the wiring, it can be diagnosed and handled in real time through the main station.
• Serial communication method. A serial cable is used to connect the PDA and the master client. The client then connects to the server database to retrieve work content and upload verification information.
A small database was also built on the PDA to store data such as meter calibrator information, meter information, and meter calibration task information. The PDA software was developed in the EVC 3.0 environment, and its module structure is shown in Figure 4.
3. System Functions and Features
Compared with traditional on-site verification of electrical energy meters, this system has the following functional characteristics:
• Automated calibration. The collected data is automatically input into the PDA via serial port or infrared communication, stored in the PDA, and then uploaded to the main station database, realizing paperless and automated operation.
• Intelligent meter calibration. The system's error wiring expert diagnostic module can assist meter calibrators in identifying wiring errors via a GPRS wireless network, improving work efficiency.
• Rational task scheduling. By generating an annual plan algorithm, and taking into account factors such as user type, last year's plan completion status, and user region, users or substations with similar calibration locations and times can be scheduled to calibrate their meters on the same day, avoiding unnecessary travel for calibration personnel.
• Standardized management. Operators have different management permissions, which facilitates the work of metrology personnel in different positions, while also ensuring the security and accuracy of the system and data.
• Information processing. All meter calibration results are ultimately summarized into various reports, such as electricity meter operating point verification reports, key electricity meter operating point verification reports, electricity meter operating point non-optimal verification reports, key electricity meter operating point non-optimal verification reports, important electricity meter operating point two-rate reports, verification result statistics, verification result analysis, etc. Moreover, all these statistical reports have corresponding statistical charts, presenting various information to the operator intuitively and conveniently.
• Strong network security. The system employs firewall and VPN technologies to keep attacks on the main server out, ensuring system security.
• Strong real-time performance. The GPRS network has the characteristics of short access time, high transmission rate and high resource utilization[5], which meets the real-time, fast and stable requirements of the system.
4. Conclusion
This intelligent on-site verification and management system for electricity meters, combining PDA and GPRS technologies, is convenient to maintain, simple to operate, and easily expandable. Compared with traditional meter calibration methods, it achieves paperless meter calibration and intelligent management, simplifies the calibration process, standardizes data maintenance by metering units, and reduces disputes and accidents. The system has already been put into use in a city in Zhejiang Province, receiving attention and praise. It is believed that its future applications will bring even greater economic and social benefits.
