Yuan Kai 1 Lu Ming 2
1 Shanghai Century Metropolitan Architectural Design & Research Institute Co., Ltd., Chongming, Shanghai 202150
2 Shanghai Acrel Electric Co., Ltd., Jiading District, Shanghai 201801
Abstract: This paper introduces a method for installing intelligent power meters and a power distribution monitoring system in a 10/0.4kV power distribution system. This system collects electrical parameters such as voltage, current, frequency, power factor, and active power, as well as switch signals, in real time. The data is then transmitted to the backend via a network, thereby enabling real-time monitoring of the power status and energy consumption of the low-voltage power distribution system.
Keywords: Power distribution monitoring system; Acrel-3000 model; RS485 communication; energy consumption monitoring
0 Overview
The ward building of Shanghai Huashan Hospital is a medical building with a floor area of approximately 20,000 square meters. In accordance with the requirements for power distribution system management and energy consumption monitoring, it is necessary to monitor the high-voltage incoming lines, low-voltage outgoing lines, and distribution boxes on each floor to ensure safe and efficient power use.
The Acrel-3000 low-voltage intelligent power distribution system utilizes the latest advancements in modern electronic, computer, network, and fieldbus technologies to perform distributed data acquisition and centralized monitoring and management of power distribution systems. It networks the secondary equipment of the power distribution system, connecting dispersed field devices into a cohesive whole through computers and communication networks, enabling remote monitoring and centralized management.
1. Composition of the power distribution monitoring system
This system adopts a hierarchical distributed computer network structure, namely the field equipment layer, the network communication layer, and the station control management layer, as shown in Figure 1.
Figure 1 System Topology
The main field equipment includes: multi-functional network power meters, digital and analog input modules, and intelligent circuit breakers. These devices are installed in electrical cabinets corresponding to the primary equipment. All devices use RS485 communication interfaces and communicate via a field MODBUS bus network to achieve field data acquisition.
The network communication layer mainly consists of a communication server, whose main function is to centrally collect data from the scattered field acquisition devices and transmit it to the station control layer, thus completing the data interaction between the field layer and the station control layer.
Station control management layer: Equipped with a high-performance industrial computer, monitor, UPS power supply, printer, alarm buzzer, and other equipment. The monitoring system is installed on the computer, centrally collecting and displaying the operating status of field equipment, presenting it to the user in a human-machine interactive format. Simultaneously, users can send commands to field equipment through the system software to achieve remote control functionality.
All the above network instruments use RS485 interfaces and the MODBUS-RTU communication protocol. RS485 uses shielded wires for transmission, typically requiring only two wires for simple and convenient wiring. The communication interface is half-duplex, meaning both parties can send and receive data, but only one can send or receive data at a time. The maximum data transmission rate is 10Mbps. The RS-485 interface uses a combination of balanced drivers and differential receivers, enhancing noise immunity. Up to 32 devices can be connected on the bus, with a maximum transmission distance of 1.2km.
2. Main functions of the monitoring system: The power monitoring computer completes the data acquisition of power parameters of each circuit through the transmission channels provided by field equipment and communication system. The information is analyzed and processed and provided to the duty officer in various forms such as reports, so that the duty officer can easily grasp the operation status of the power supply system, including the operation status of related equipment.
2.1 The operation and protection information acquisition system collects parameters from the intelligent measurement and control unit, including telemetry signals from the low-voltage main incoming line, bus tie, and outgoing lines. This includes voltage, current, active power, reactive power, power factor, frequency, active energy, reactive energy, and various alarm information for each circuit.
2.2 The human-machine interface system provides a simple, easy-to-use, and user-friendly interface. It displays the status of power distribution system equipment and corresponding real-time operating parameters according to the substation's specifications.
The system software provides fully functional graphic editing software, allowing users to customize the display methods of various graphic elements and devices in various states according to actual conditions and past habits.
Includes the following functional features:
The full-graphic editing interface has a variety of display features, allowing users to intuitively and conveniently edit, locate, and view relevant information and content.
It provides screen management tools, which can suggest related screens, quickly recall important screens, select screen file indexes, and automatically recall screens in case of an accident.
It provides multiple numerical display methods, including bar charts and curves. Users can also customize flashing, color changing, and special symbols according to their needs and habits, based on the numerical status and system status, to distinguish between normal, upper limit, and lower limit conditions of various data, including telemetry data.
Screen display: Chinese LCD display, with selectable graphic colors, flashing, animation, and other means to fully represent the operating status diagrams and operation screens, practical parameter tables of the power distribution system, various operation tickets and reports, accident and fault alarm displays, and operating status displays of the measurement, control, and protection units; screen display response time is 1 second. See Figure 2.
Figure 2 Power Distribution System Diagram
2.3 Statistical analysis, reports, and printing of electricity consumption statistics for hours, days, months, and years; user-defined report formats and calculation methods; scheduled printing, call-to-action printing, and event log printing of all reports; real-time and historical data retention for more than 2 years in the database; summary statistics of operating parameters of various electrical equipment and systems, and generation of various reports according to user requirements, including: hourly, daily, monthly, quarterly, and annual reports; see Figure 3.
Figure 3 Summary Table of Electrical Parameters
Statistical reports on parameters and extreme values of various devices; statistical reports on the operation of the entire system, etc. For event logs, alarms and data reports, printing can be set to be scheduled and can be initiated as needed.
Energy statistics reports and printing: summarizes and statistically analyzes energy consumption, and generates various reports according to user requirements, including: hourly, daily, monthly, quarterly, and annual reports; energy consumption statistics reports, daily, monthly, and annual active/reactive energy statistics, and outputs energy reports in the user's standard format, realizing the transformation from manual meter reading to automatic reporting. It can be set to timed printing and on-demand printing as needed, as shown in Figure 4.
Figure 4 Electricity Report
2.4 The historical data and trend analysis system collects real-time data from various monitoring, control, and management devices and stores it in an open database. The system can save historical data for long periods (many years). The system can retrieve and print the above historical data at any time using standard and configurable file formats.
Based on historical data records, annual, monthly, and daily changes and real-time data trend analysis of various parameters can be performed. Classification and comprehensive comparative analysis can be conducted to provide a basis for business process optimization and equipment and facility utilization optimization, as shown in Figure 5.
Figure 5 Current trend curve
2.5 System Security This system software has hundreds of password partitions and security levels, providing tiered passwords for system administrators, engineers, shift supervisors, and general on-duty operators. It also automatically records all operations with time stamps, enabling robust anti-incident measures, as shown in Figure 6.
Figure 6 User Permission Management
2.6 Fault Analysis and Equipment Maintenance Management System: Based on time-stamped event records and waveform records, the system can perform cause analysis of faults and events. In addition, the system can statistically analyze the status parameters and cumulative life parameters of equipment such as switches, and make equipment maintenance forecasts accordingly; see Figure 7.
Figure 7 Event Log
2.7 Protection Information Management: Manages protection settings and protection action information, and provides relevant query functions.
2.8 Other Functions Other daily management functions include operation record and shift handover record management, equipment operating status, defect and maintenance record management, and rules and regulations. The management functions meet user requirements, are applicable, convenient, and facilitate resource sharing. Various documents can be stored, retrieved, edited, displayed, and printed.
2.9 System Self-Diagnosis Function This system software can diagnose the operating conditions of various software and hardware online. When abnormalities and faults are detected, alarm information can be displayed and printed in a timely manner, and displayed in different colors on the operating condition diagram.
Because the system has redundant equipment, it can automatically switch to the backup system when a software or hardware failure occurs.
3. Conclusion
With the rapid development of society, users have increasingly higher requirements for the automation and intelligence of power supply and distribution. Realizing unmanned operation of power distribution rooms has become a future direction for the development of power distribution automation. The ACREL-3000 power distribution monitoring system is a good solution for high-quality operation of power supply and distribution. Operation has shown that the system is reliable, safe and stable, and reduces equipment operating costs while improving the quality of power distribution automation.
References:
Ren Zhicheng and Zhou Zhong, eds., *Principles and Application Guide of Digital Instruments for Power Measurement*, China Electric Power Press, April 2007.
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