SummaryThe design of the 35kV substation integrated automation system primarily adheres to the overall needs of power grid dispatch automation, ensuring its configuration and functions meet requirements for grid safety, economy, hierarchical information transmission, and resource sharing. This article takes the design of 35kV and below substation automation systems as the guiding thought, discussing the relevant design work.
KeywordsTransformer Substation; Distribution Network; Comprehensive Automation; Main Electrical Wiring; Transformers
0 Introduction
The construction of a substation within the 35kV and below area of the chemical plant is a crucial project within the factory. Throughout the construction process, due to factors such as high technical requirements, substantial investment, and numerous power facilities, there is a high demand for the capabilities of the substation staff. Therefore, the management department must enhance the operation and management level of the substation to achieve automation, thereby improving the reliability and economic benefits of the substation operation.
In this context, the use of new micro secondary devices and their replacement of traditional discrete devices have strengthened functions such as protection, control, monitoring, and remote operation. This has achieved the sharing of equipment and information, making substation design and layout more streamlined and compact, as well as safer and more reliable in operation. The integrated control system of the substation utilizes modern computer and communication technologies to transform the original secondary equipment structure, significantly simplifying the system architecture. Not only does it enable data sharing, but its wiring structure is also more straightforward, and the secondary equipment occupies less space, giving substation with voltages below 35kV a completely new look [1].
1. Electrical Main Wiring Scheme Analysis
The main circuit should be designed with principles of reliable operation, simplicity, clarity, and scalability. The proposed design features transformer feed-in and internal bridge lines primarily for 35kV circuits, with 10kV busbars employing segmented busbar wiring. There are 25 10kV outgoing lines, including two capacitive compensation lines, with all 10kV lines equipped with high-voltage vacuum circuit breakers. The transformer neutral grounding is as follows: the 35kV side is not grounded, while the neutral point on the 10kV side is grounded through an arc suppression coil. All 10kV lines are cabled. Therefore, arc suppression coils are used for compensation. Due to the absence of a neutral point on the 10kV main transformer side, a shared grounding transformer with the substation and arc suppression coil is employed, allowing for adjustment of each arc suppression coil's capacity. This design is based on a 300MVA short-circuit capacity, analyzes short-circuit currents, and determines the selection of the equipment.
The main transformer selected is an energy-saving, low-loss, and on-load tap-changing transformer (model S11-35), with a capacity determined by the actual and planned load of the power supply area, reaching 20MVA. The 35kV equipment uses fully enclosed composite insulated metal-enclosed switchgear, which houses high-voltage vacuum switches. The main transformer is a three-phase double-wound self-cooled on-load tap-changing transformer S11-20000/35, with an impedance voltage of Uk%=8.35±3×2.5%/10.5kV. The 10kV equipment employs a metal-enclosed mobile switchgear, internally fitted with high-voltage vacuum switches. From the perspective of measurement accuracy, the transformers have all reached a 0.2s measurement precision. The 10kV busbar sections are equipped with a set of shunt capacitors and a set of arc-suppression coil equipment.
Roof-top lightning protection mesh installed to prevent direct lightning strikes. Metal oxide varistors with excellent protective performance are used at the 35kV and 10kV busbars, capacitors, and 10kV outgoing lines. The dispatching and management of the 35kV substation should send remote measurement, remote signaling, and remote control information to the superior 220kV substation. The common measurement and control equipment is centralized in the power monitoring room. The power supply is provided by the 10kV transformer of the SBH15-M-630/10 substation, which is connected to the 10kV busbars. Worklights and emergency lights are installed throughout the substation, with the emergency lighting circuit automatically switching to EPS power supply in the event of a power outage.
2 35kV Substation Main Power Distribution Scheme
Through various data analyses, it has been found that using low-loss energy-saving transformers is an effective way to reduce power losses. When voltage deviation does not reach the specified value, the 35kV step-down substation should prioritize the use of on-load tap-changing transformers. The main circuit of a 35kV substation typically consists of single bus, single bus sectioning, double bus connection, unit connection, internal bridge, and external bridge, with the specific implementation determined by the actual situation [2]. The main circuit of a 35kV substation should be decided based on the substation's position in the power grid, the number of incoming and outgoing circuit paths, equipment characteristics, and load characteristics. It also needs to meet the requirements of reliable power supply, flexible operation, convenient maintenance, cost savings, and ease of expansion.
The main lines of the substation should meet the basic requirements of safety, reliability, flexibility, and economy. Safety encompasses both equipment and personnel safety. Reliability should meet the requirements of primary and secondary loads for power supply reliability. The use of small switches allows for flexibility in various operating conditions, ease of maintenance, and the ability to adapt to load development, facilitating expansion, and simplifying wiring as much as possible, reducing investment and land use, and lowering operating costs. There are generally two types of 35kV substations: indoor and outdoor. Indoor substations are easy to operate and maintain, and occupy less space. Outdoor substations, on the other hand, have lower construction costs, can accommodate alarm systems, and have good heat dissipation. It is evident that the advantages of indoor and outdoor substations complement each other, as factory floor space is limited; therefore, an indoor layout has been adopted, featuring 35kV and 10kV distribution equipment, with the main transformer installed indoors.
Power Supply Reliability Analysis
Reliability in power supply refers to uninterrupted electricity. Power outages not only affect chemical plant production but also cause damage to equipment. In severe cases, they can lead to injuries or even deaths, explosions, and significant negative consequences. For instance, power outages can impact the operation of key production equipment, leading to disruptions in critical processes and substantial economic losses, even if power is restored, which may take a considerable amount of time. To ensure power reliability, a dual-circuit power supply model must be implemented for these critical power-consuming equipment. It's essential to maintain the quality of power supply and meet technical specifications for voltage fluctuations.
AC frequency directly impacts the performance of AC motors, and changes in frequency can affect their speed. In "Electrical Energy Quality and Power System Frequency Deviation," the standard for AC power with a 50Hz rated frequency requires that the frequency deviation from the nominal value not exceed ±0.2 to ±0.5Hz, which is equivalent to ±0.4% to ±1% [3]. Voltage limitation is another important indicator of grid quality. Voltage deviation refers to the difference between the actual voltage of electrical equipment and the rated voltage during operation. Energy-consuming equipment has a certain degree of adaptability to voltage deviation, but when the deviation increases, it can affect the performance of electrical equipment, even leading to equipment failure. For example, incandescent bulbs will reduce their lifespan by half when operated at a voltage exceeding their rated voltage by 5%. Therefore, there are clear regulations in China regarding voltage deviation for electrical equipment. For instance, the voltage deviation for motors should not exceed ±5% of the rated voltage, and for bulbs, it should not exceed -3% and -2.5% of the rated value.
Overall Design Analysis of Substation System Data Link
4.1 Comprehensive Automation System Structure
The substation integrated automation system employs a hierarchical distributed structure. The hierarchical distributed monitoring system achieves information resource sharing, fully utilizes the overall resources and efficiency of the computer system, and is currently the mainstream method for monitoring systems. The system includes an isolation layer and a station control layer, with the isolation layer and station control layer interconnected via dual Ethernet. It conforms to the IEC61850 standard. The isolation devices include I/O measurement and control devices, relay protection devices, multifunctional electrical meters, low-voltage motor protectors, and other intelligent equipment. All intelligent devices are connected to the station control layer through a communication manager and an Ethernet switch. All intelligent devices support Modbus communication protocols. Communication management machines are set up at the interval layer, which should use industrial communication computers with embedded applications. All serial port devices are connected to the station control layer through communication management machines (using Modbus communication protocols) and Ethernet switches. All Ethernet devices connect to the station control layer after being connected to the local switch via the Ethernet interface. All communication interfaces have isolation and protection functions.
The station control layer equipment primarily handles the invocation of various monitoring images and graphical curves, issuance of control commands, generation of reports, operation tickets, databases, management and printing, alarm notifications, and printing, monitoring, and management of the control intermediate layer devices, forming a comprehensive station monitoring system, central control center, and communication with remote monitoring centers. The station control layer is mainly composed of monitoring master stations, engineer stations, integrated application servers, database servers, protection and management workstations, OPC servers, communication servers, printers, and other equipment. The monitoring master station operates in a dual-active hot-standby mode, with the normal operation being completed by the monitoring master station, while the standby master station remains in a hot-standby state. In the event of a failure in the monitoring master station, the standby master station immediately takes over as the monitoring master station, assuming all the functions of the monitoring master station. Once the monitoring master station resumes normal operation, the control is handed back to it, and the standby master station remains in hot-standby mode, ensuring a seamless dual-active switch without any disturbances.
4.2 Control System Data Flow
Control systems are segmented into multi-layered structures as required, including the device layer at the bottom, the intermediate layer, and the station control layer. High-speed network communication is utilized within and between layers, with communication mediums being either network cables or optical fibers.
The platform software is designed to align with the management methods of operation areas, oil production areas, and metering stations. It perfectly matches the actual management practices. Additionally, considering the system as a platform, each page is managed through a database approach, making it highly adaptable for third-party software integration and other expandability features.
4.3 Subsystem Description
4.3.1 Monitoring Function
Data Collection and Processing: Acquisition of analog and digital quantities, temperature measurements, and other parameters from the production process, including CT, PT, protective equipment for power distribution systems, DC systems, and power systems. Alarm handling is divided into two categories: accident alarms and pre-alarm notifications. Printing and recording are performed by the computer control system, which outputs the required information through printers in accordance with specified formats. Statistical computation involves the statistics, analysis, and calculation of real-time data.
System status monitoring involves supervising switch signals such as circuit breaker positions and isolator switch positions, as well as monitoring the device's self-check, circuit breaker trip due to faults, bus grounding, and various protective action signals. Operator workstations can dynamically display key electrical parameters, communication status, faults, and protective action states in digital, textual, graphical, tabular, and curve formats. Every loop is monitored, and changes in operating parameters and statuses during the monitoring period are displayed on the screen.
In the event of communication failure, data during the interruption can be automatically restored or awakened, and alerts are issued when anomalies occur to ensure the continuity, completeness, and accuracy of the data. The system can also monitor various power supply parameters, including conventional electrical parameters such as voltage, current, and frequency, as well as active, reactive, MD, and harmonic components, keeping all circuits under the surveillance of the comprehensive self-monitoring system [4].
Database maintenance allows engineers to interactively modify, add, and delete data items within the database online. The graphical interface displays various information on the screen in real-time via reports, graphics, and audio-visual means. Clock synchronization is monitored by the computerized control system at the substation, which receives timed signals from the navigation system and synchronizes every clock-equipped device, such as isolators and station computers, to ensure clock synchronization rates meet requirements. Maintenance functions are managed, maintained, and expanded by substation staff at workstations. Incident records include protective action information, changes in circuit breaker/status, input/output of protective functions, local/remote switching, interlock control commands, and automatic alarms.
Energy management automatically calculates the power consumption of each device on a daily/natural month/natural year basis. By comparing data, it calculates the energy efficiency of each device, making it convenient for users to add/remove power circuits. Operation tickets can be automatically generated based on work tickets, and they also have an operation simulation function to verify the correctness of operations. Simulation training utilizes various forms such as textual explanations, images, videos, 2D animations, virtual simulations, etc., creating a richly illustrated, audio-visual, and interactive experience.
4.3.2 Management Function
Equipment Management: Establish a unified dynamic equipment inventory, focusing on all equipment's historical operating status, maintenance and repair plans, repair history, defect information, replacement history, maintenance history, and spare parts status. Update the equipment inventory dynamically through the equipment in/out process, installation/uninstallation process, and maintenance/replacement process, ensuring the inventory aligns with the actual on-site equipment. This supports the full lifecycle management of equipment.
AcrelCloud-1000 Substation Operation and Maintenance Cloud Platform
5.1 Overview
The cloud-based management platform developed based on technologies such as the Internet+, big data, and mobile communication, meets the needs of users or operation and maintenance companies to monitor the operation status and parameters of numerous substation loops, indoor environmental temperature and humidity, cable and busbar operating temperatures, as well as on-site equipment or environmental scenes. It achieves centralized storage and unified management of data, facilitating easy access. It supports authorized users to access, receive alerts, and complete daily and regular inspection and dispatching tasks through various terminals like computers, smartphones, and tablets.
5.2 Application Venue
New and expanded substation operation and maintenance systems for industries such as telecommunications, finance, transportation, energy, healthcare, culture and sports, education and scientific research, agriculture, forestry, water conservancy, commercial services, and public utilities.
5.3 System Architecture
The system is divided into four layers: the perception layer, transmission layer, application layer, and presentation layer.
The perception layer includes multifunctional meters, temperature and humidity monitoring devices, cameras, and switch quantity collection devices installed at the substation. Except for the cameras, the other equipment is connected to the site's intelligent gateway via the RS485 bus, interfacing with the RS485 port.
Transmission Layer: Comprises on-site intelligent gateways and switches, etc. The intelligent gateway actively collects data from equipment in the field device layer, performs protocol conversion, data storage, and uploads the data to the server port through the switch. In case of network failure, data can be stored locally and continued to be uploaded from the interrupted point upon network recovery, ensuring that no data is lost on the server side.
The application layer includes the application server and the database server. If there are fewer than 30 substation facilities, the application server and database server can be configured together. The servers must have a fixed IP address to receive data actively transmitted from various intelligent gateways.
The Display Layer: Users can access platform information through multiple terminals such as smartphones, tablets, and computers.
5.4 System Functionality
5.4.1 Energy Consumption Monthly Report
The Energy Consumption Monthly Report supports users in querying the electricity consumption of managed stations by total electricity usage, substation name, substation number, etc. The query range can be set to a monthly basis.
5.4.2 Site Monitoring
Site monitoring includes an overview, operational status, daily event logs, hourly electricity consumption curves for the day, and an overview of electricity usage.
Transformer status supports users in querying all or specific substation transformer power, load factor, and other operating status data. It allows for ranking in ascending or descending order based on load factor and power.
Operations showcase the location and total information of substation users on the map.
5.4.5 Power Distribution Diagram
The distribution diagram showcases the power distribution information of the selected substation. It illustrates the switch status and operating conditions, such as current, of each circuit, and supports detailed queries for operating parameters including voltage, current, and power.
5.4.6 Monitoring
The monitor displays the current live feed, allowing you to select a substation to view its information.
5.4.7 Power Operation Report
The power operation report shows the real-time and average values of the operating parameters and electricity meter readings for each loop of the selected equipment at the selected station, with a statistical analysis of the collection intervals.
Alert Message 5.4.8
Analyze all alert information on the platform.
5.4.9 Task Management
The task management page allows for the posting of inspection or corrective tasks, viewing the status and completion of inspection or corrective tasks, and clicking to view specific inspection details.
5.4.10 User Report
The User Report Page is primarily used to automatically compile one month's operational data for selected transformer substations. It provides statistical analysis of transformer loads, power consumption of distribution circuits, power factor, and alarm events, and lists various defects found during inspections within the specified period, along with their handling situations.
5.4.11 APP Monitoring
3.12APP supports the "Monitoring System," "Equipment Records," "To-Do List," "Inspection Records," "Defect Records," "Document Management," and "User Reports" modules for power operation and maintenance on mobile devices. It offers features such as one-time diagram, demand, electricity consumption, curves, temperature and humidity, year-on-year and month-on-month comparisons, power quality, and various event alarm queries, as well as equipment records search, to-do event handling, inspection record queries, user reports, and document management.
6 Conclusion
The 35kV substation comprehensive automation control system in the chemical factory area has addressed the deficiency of traditional protection devices in external communication. It integrates multiple key modules such as control, protection, data collection, monitoring, and data transmission, achieving data sharing. The system includes protection devices, data collection devices, event and fault recording devices, control operation interlock devices, synchronization devices, communication devices, data processing and recording devices, and self-diagnostic devices.
In recent years, an increasing number of chemical industrial zones have adopted computer-integrated automation in their 35kV substation facilities, with many of these facilities coming online sequentially. This trend underscores the growing maturity and unparalleled advantages of 35kV substation automation technology in chemical industrial zones. It aims to reduce personnel, enhance efficiency, lower construction costs, ensure reliable substation operation, and improve economic benefits.
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