Summary: Substations primarily handle electrical energy consumption, transmission, and distribution. Among them, the most critical component is the substation switchgear, which is numerous in quantity and interdependent among each unit. In daily operations, if a substation switchgear stops functioning or encounters an accident, it can impact the entire transmission and distribution system of the substation, potentially causing significant incidents.
Substation Switchgear; Equipment Wireless Temperature Measurement System
0 Introduction
During the long-term operation of substation high-voltage switchgear equipment, the contacts, busbars, and power cable connections within the switchgear can overheat under normal load due to aging, poor contact, and loosening. If the temperatures of these components cannot be effectively monitored, it could lead to the failure of the entire substation's operation. Designing a practical temperature detection system for rapid and accurate monitoring of the switchgear is a crucial research topic.
Current Research Status and Trends in Global and Domestic Markets
1.1 Infrared Imaging Temperature Measurement
Infrared thermal imaging temperature measurement first appeared in Sweden in the last century. Due to its inherent advantages, it has gradually gained rapid development. Simply put, the principle of infrared imaging is that any object has its own temperature and emits heat to the outside world. The intensity of the emitted heat can qualitatively depict the object, which can be visualized through different colors, making it simple and intuitive to identify. The infrared thermal imagers we commonly see are based on this principle. Used on switchgear, they can map the intensity of heat emitted by the equipment inside the cabinet through special instruments, allowing for a direct observation of heat intensity without manually opening the switchgear, thus reducing potential personnel losses and dangers. In our country's large power industry, infrared thermal imaging technology was first introduced and has been widely praised and applied.
The technical feature of infrared imaging technology is that it can detect temperatures without interrupting the operation of electrical equipment, which is particularly suitable for substation applications. However, infrared imaging technology has its drawbacks. The essence of infrared technology lies in emitting different infrared rays, but their penetration ability is not very strong, especially when encountering hard objects or thick iron plates, where their capability is greatly reduced. Moreover, infrared rays are highly dependent on the external environment, and different environments can also affect the accuracy of temperature information transmission. Therefore, in summary, infrared measurement technology used in substation switchgear cannot make a relatively accurate prediction and its precision is not high.
1.2 Fiber Optic Temperature Measurement
Over the past few decades, optical fiber technology has rapidly developed since its inception. The advantages of optical fiber technology are self-evident and do not require extensive introduction. Compared to cables, it boasts significant advancements in terms of size, minimal additional protective measures, and its ability to transmit data entirely through light, rendering it highly resistant to electromagnetic interference. This makes it particularly suitable for use in environments with strong magnetic fields, such as substation facilities. Optical fiber temperature measurement is more commonly used in switchgears than infrared measurement due to its superior benefits. Currently, there are two primary applications in switchgears: using optical fibers as temperature sensors and using them as signal transmission media. However, while the advantages of optical fiber transmission are numerous, employing it as the transmission medium between switchgear sensors and the main station, along with semiconductor temperature sensors as probes for measuring internal temperatures, has its drawbacks. Firstly, the cost of optical fiber transmission is expensive, making it more suitable for long-distance transmission, whereas the distance between substation switchgears and the main station is relatively short, with the furthest being only a few dozen kilometers. Additionally, the poor interference resistance of semiconductor temperature sensor probes, which cannot adapt to the harsh environment of substation facilities, is another reason for the method's disuse.
1.3 Non-Contact Temperature Measurement
Typically, temperature measurement is divided into active and passive types. The simple measurement principle of active wireless temperature measurement involves placing a temperature sensor (usually a DS18B20) on the component to be measured, collecting the temperature information of the component (in digital signals), and then transmitting the temperature signal via wireless communication. The power supply method is battery-powered. The drawback is that the sensor probe and wireless transmitter circuit are powered by batteries or small current transformers, which have issues such as short battery life and difficulty in replacement, as well as challenges in controlling the current size and installation difficulties with transformer power supply.
Characteristics of High-Voltage Switchgear Temperature Measurement
Online temperature measurement for high-voltage switch cabinets has special regulations, distinct from standard temperature measurement procedures.
(1) The high-voltage insulation issue of the temperature device stands out.
The high-voltage switchgear transmits the measured high-voltage temperature data through the internal temperature sensing device and the external temperature receiving device of the cabinet. At the same time, high-voltage insulation phenomena occur on both the high-voltage and low-voltage sides inside and outside the cabinet. Effective isolation measures must be implemented to prevent insulation faults.
(2) The original functions of the switchgear are unaffected by the temperature measurement device.
The switchgear is composed of circuit breakers and cabinets, with the operable device being the circuit breaker. Therefore, the operational functions of the operable devices such as circuit breakers are not affected by temperature measurement equipment.
(3) Infrared temperature measurement and other methods are not adaptable to the on-site switchgear structure.
The switchgear is composed of circuit breakers and cabinets. The insulated heat-shrink packaging is designed for the conductive parts within the cabinet to minimize the entry of small organisms, which can cause short circuits and flashovers due to moisture and dirt inside the cabinet.
Severe Electromagnetic Interference in the Operating Environment of High-Voltage Switchgear
Electromagnetic radiation is inevitably produced inside the cabinet, through the current, and within the substation, which can weaken the temperature measurement system's performance and reduce the accuracy of temperature data. Measures to minimize errors and appropriate calibration procedures should be adopted to improve the accuracy of temperature readings.
Hardware Design for the 3 SAW Temperature Measurement System
3.1 Temperature Data Collection
Typically installed on the surface of the tested part, such as busbar connection joints and exposed contact points within high-voltage switchgear. The wireless temperature collector, designed for the detection and transmission of temperature signals, consists of a temperature sensor, measurement circuit, logic control circuit, and wireless transmission and reception circuit.
The temperature sensor is the lowest component in the cabinet for measuring internal temperatures. It employs a saw to detect temperature information. The wireless transmission circuit uses 433MHz electromagnetic waves. Once the SAW sensor head inside the switch cabinet receives the signal, it converts it into its own energy and modulates the measured contact temperature onto the electromagnetic wave. The modulated data is then transmitted wirelessly to the collection terminal, enabling real-time acquisition of the temperature information at the measured point, thereby achieving non-contact temperature measurement.
3.2 System Communication Implementation
The communication management device serves as the intermediary bridge connecting various components, transmitting temperature information detected by the temperature sensors within the switchgear to the information monitoring center of the power supply company's dispatching hall. The safety and speed of the communication system are also one of the reasons for determining the overall effectiveness of this system. The information communication system enables measurement control, communication management, data collection, and data processing for various types of temperature measurement components or units within switchgears. It sends the detection results and equipment status to the station control center and remote monitoring and data collection management system via a dedicated internal network built for power grid communication.
With the development of modern industrial distributed control systems, RS-485 communication has emerged as a digital transmission method that offers enhanced resistance to electrical noise interference and the ability to transmit over greater distances. The RS-485 standard is reasonable for transmission distances between substation and control rooms of dispatch centers, boasting several advantages such as fast transmission rates and strong anti-interference capabilities. It is often utilized as a relatively economical communication platform with high noise suppression, relatively high transmission rates, long transmission distances, and wide common mode range.
3.3SAW Temperature Measurement System Software Design
The software design portion of the SAW-based temperature monitoring system allows for direct testing and monitoring of the system's operational status, with simulations displayed directly on the computer. The system's initial phase involves self-inspection to ensure reliable operation, followed by temperature monitoring, which is primarily divided into two parts. The first part is temperature detection, starting with the collection of temperature data, signal transmission, data analysis and diagnostics. The temperature data collection is the first-hand data gathered by acoustic surface wave sensors installed at critical temperature measurement points on high-voltage equipment within the switchgear. This data is then wirelessly transmitted to the collection terminal, where it is calculated and compared to the set temperature to determine if there is an overheating condition. The second part involves the temperature system's alarm function. If an overheating condition is detected, the alarm system triggers an alert through the alarm device to notify relevant staff for timely intervention. Additionally, the overheated data is printed for reference. Regardless of whether there is an overheating condition or not, the information must be visible on the screen in the dispatch and monitoring center.
4 Ankoray Wireless Temperature Measurement System
4.1 System Structure
The Acrel-2000T Wireless Temperature Monitoring System communicates directly with equipment at the bay level via RS 485 bus or Ethernet. The system design adheres to international standards such as Modbus-RTU and Modbus-TCP, significantly enhancing security, reliability, and openness. The system features remote signaling, measurement, control, adjustment, configuration, event alarms, trend charts, bar graphs, reports, and user management. It can monitor the operational status of wireless temperature measurement system devices, achieve rapid alarm response, and prevent severe faults from occurring.
Structure Diagram of Temperature Online Monitoring System
4.2 System Function
The Acrel-2000T temperature monitoring system has been installed in the duty monitoring room, enabling remote monitoring of the operating temperatures of all switchgear within the system. The system boasts the following main features:
Temperature Display: Shows the real-time values of each temperature measuring point within the power distribution system, and allows for remote data viewing via computer WEB or mobile APP.
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Temperature Trend Curves: View the temperature trend curve for each temperature sensing point.
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Operation Report: Query and print temperature data for each temperature sensing point.
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Real-time Alerts: The system can issue alerts for abnormal temperatures at various temperature sensing points. It features real-time voice alarm capabilities, enabling voice alerts for all events. The alert methods include pop-up windows, voice alarms, and can also send alert messages via SMS or APP push notifications, promptly reminding on-duty staff.
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Historical Event Inquiry: Capable of storing and managing records of events such as temperature limits, facilitating users to trace historical system events and alarms, and conduct inquiries, statistics, and accident analysis.
4.3 System Hardware Configuration
The temperature online monitoring system is primarily composed of temperature sensors and temperature collection/display units at the equipment layer, edge computing gateways at the communication layer, and the measurement system host at the station control layer, enabling online temperature monitoring of critical electrical parts in the power distribution and transformation system.
5 Conclusion
Substation switchgear is crucial for voltage transmission. As the saying goes, "If you want to do a job well, you must first sharpen your tools." The development level of materials is key to the device. Currently, the research direction of new sensitive materials includes the study of thin film materials and composite piezoelectric materials, etc. Therefore, to enhance the accuracy and sensitivity of sensors during actual measurements, the manufacturing process needs to be improved.
Reference:
Sun Lei, Jia Zhenwei. Research on a Wireless Temperature Measurement System for Equipment in Substation Switchgear Cabinets
Liao Xuesong. Research on Online Temperature Monitoring System for High-Voltage Switchgear [D]. Nanchang University, 2007.
[3] Ankorree Enterprise Microgrid Design and Application Manual, 2020.06 Edition.
[4] Ankoray's User Substation Power Distribution and Monitoring Solution, October 2021
