1 Introduction
From power plants, substations, and high-voltage transmission lines to urban and rural power grids, the temperature change of electrical contacts is a crucial indicator of the safe and stable operation of the entire power grid. However, temperature changes require comprehensive consideration of operating conditions such as load and weather, and are unpredictable, making it a major concern for the power system.
With the promotion and application of substation automation technology, unmanned substations are becoming increasingly common. The high-voltage switchgear in these substations employs a fully sealed structure. During long-term operation, the contacts and busbar connections of the switches can overheat due to aging or excessive contact resistance. Since the temperature of these overheated components cannot be monitored, the operating conditions of the equipment become increasingly harsh, significantly increasing the probability of equipment accidents such as contact meltdown and disconnector burnout within the high-voltage switchgear. A wireless temperature monitoring system for substations, based on electromagnetic wave signal transmission, can monitor the operating temperature of high-voltage equipment such as high-voltage switchgear in real time, enabling timely detection and handling of potential equipment hazards. This is of great significance for improving equipment management and power supply reliability.
2. Composition of the wireless temperature measurement system in the substation
The substation wireless temperature measurement system consists of a wireless temperature measuring nut, a wireless receiver box, a signal router, and a back-end management system. It monitors the temperature of components such as high-voltage switchgear, busbar joints, and outdoor disconnect switch contacts in power plants/substations in real time.
The configuration of the substation wireless temperature measurement system is shown in Figure 1;
1. Temperature-sensing nut: Installed on the current-carrying component requiring temperature measurement, it has a built-in temperature control switch. When the nut temperature exceeds the switch temperature (e.g., 60 degrees Celsius), the internal circuit of the nut is activated, starting to collect the nut temperature and transmitting a temperature signal via RF.
2. The receiver box receives the RF radio frequency signals from each nut and saves the nut temperature, waiting for the main station to query it;
3. Each receiver box is connected in parallel via an RS485 bus, and then directly connected to the main station PC via an RS485 to RS232 converter:
4. The master station continuously polls each receiving box to query temperature information, and the receiving box sends the temperature information of each nut to the master station;
5. The receiving box does not save historical temperature information, but only retains the current nut temperature information. That is, the receiving box stores a current temperature mapping table for each nut.
6. The historical temperature information of the nut is stored by the main station:
7. The receiver box does not limit which nuts' information it receives; that is, it only represents the nuts that are actually received.
8. The background monitoring host enables functions such as querying historical data, issuing over-temperature alarms, and sending notifications.
3. Main features of the wireless temperature measurement system for substations
The substation wireless temperature measurement system, based on electromagnetic wave signal transmission, employs advanced and mature sensing technology and unique advanced wireless communication technology for high-voltage isolation and signal transmission. Leveraging its inherent insulation and anti-electromagnetic interference properties, it fundamentally solves the problem of difficult temperature monitoring of electrical contacts in power plants and substations. The system measures the temperature at each set point online and wirelessly uploads the data to a local temperature display, enabling over-temperature alarm functionality. It can also connect to the power automation system, allowing remote monitoring of equipment operating temperatures from a central control room, triggering remote alarms and timely detection of potential hazards. This system has the following main features:
1. Temperature sensing nut uses online/solar power. The nut adopts online/solar power, which greatly improves the service life of the terminal and extends the safe operation period of the substation wireless temperature measurement system, with a service life of up to 8 years or more.
2. A temperature alarm threshold is set. If the collected temperature data exceeds this threshold, an alarm message will pop up on the backend monitoring interface, prompting staff to take necessary measures via audio and visual means, and even directly notifying relevant personnel via SMS. This improves the efficiency of on-site equipment management for managers and achieves fully information-based management.
3. When the wireless sensor transmits the temperature of the monitored point, it also transmits its own serial number (D number). The computer automatically determines the temperature of each monitoring point based on the relationship between the sensor serial number and the installation location stored in the database in advance, thus increasing the automation level of the system.
4. The sensor and temperature measurement terminal are connected wirelessly, which facilitates the installation and maintenance of the system, reduces the impact on the safe operation of the power grid, and ensures the system's safety.
5. Continuous online monitoring 24 hours a day. The sensor automatically transmits temperature data from the monitoring point once per hour (which can be preset). The computer collects and records the temperature data from all monitoring points in real time, and immediately alarms when an anomaly is detected. The system has good real-time performance.
6. Wireless communication operates at ISM frequencies such as 433MHz and 95MHz, which are harmless to the human body and cause no electromagnetic interference to surrounding equipment, complying with FCC standards and national wireless management regulations.
7. The system has trend analysis capabilities.
8. Temperature data measured at each monitoring point can be analyzed in real time and stored for a long time. For monitoring points where the temperature changes gradually, an early warning is issued before the temperature reaches the upper limit, eliminating potential problems in their infancy.
9. The temperature measuring nut has a volume of 8mm*27mm (maximum diameter), which is very compact and can be easily installed in the high-voltage cabinet. During installation, simply tighten this device onto the bolts at the contact point. No additional equipment or changes to the structure of the original equipment are required.
10. Flexible expansion, not limited by groups; each wireless receiver box can receive data sent from up to 90 nuts.
4. Application Examples of Wireless Temperature Measurement Systems in Substations
The 110kV Dazhou Substation is an important load station in the Gaoyao power grid. In order to facilitate real-time monitoring of equipment operation, detect potential safety hazards early, and ensure the safe and stable operation of equipment, a wireless temperature measurement system has been installed at Dazhou Substation to enable online temperature measurement of the eight 10kV high-voltage switchgears that are subject to heavy loads and cannot be measured in real time.
By installing a wireless temperature sensor at each of the four locations (A, B, and C) of each switchgear cabinet—the upper and lower isolating stationary contacts, the switch wiring, and the outgoing cable head of the outgoing cabinet—real-time wireless temperature monitoring of 96 test points across eight high-voltage switchgear cabinets is achieved. This system has a total of 96 sensors, configured to trigger alarms above 60 degrees Celsius and send alerts above 80 degrees Celsius. Alarm information is directly sent to the substation manager via SMS.
The system was put into operation on June 15, 2010. In the month since, it has been operating well overall, issuing 23 alarm messages. The system not only achieved real-time monitoring of the temperature of various parts of the eight high-voltage switchgear, but the substation manager also promptly addressed two equipment overheating defects based on the alarm messages, ensuring the safe and stable operation of the equipment. Figures 2 and 3 show the monitoring information retrieved from the system.
Figure 2 clearly shows the status of the 96 temperature sensing nuts installed, allowing you to clearly see the actual temperature of each temperature sensing point. Temperatures exceeding the alarm value (set to 60 degrees Celsius) are marked in red, making it easy to check the operating temperature of the equipment.
Figure 3 clearly shows the temperature curve of the 5184 C-phase disconnect switch line side from July 14th to July 15th, 2010. The temperature trend can be used to perform effective temperature change trend analysis on a specific component.
5. Selection of Acrel ARTM Series Electrical Contact Online Temperature Measurement Products
Acrel Electric's wireless temperature measurement solution for electrical contacts consists of a wireless temperature sensor, transceiver, and display unit. The temperature sensor is directly installed at heat-generating contacts such as moving contacts, stationary contacts, cable joints, and busbars of the circuit breaker. The temperature data is transmitted wirelessly to the receiving device via radio frequency technology, and then the receiver communicates via RS-485 to the temperature measurement terminal or wireless temperature measurement system (as shown in Figure 4). This allows operating personnel to check the real-time temperature of each contact within the cabinet at any time, monitor the operating status of each contact, and promptly detect and troubleshoot faults, greatly improving the reliability and economy of the power grid operation.
5.1 Acrel Wireless Temperature Sensor
There are five types of wireless temperature sensors, corresponding to bolt fixing, strap fixing, cable tie binding, and alloy plate fixing installation methods. For different substation requirements, the appropriate sensor can be selected based on its power supply method, installation location, and ease of installation.
5.2 Acrel Wireless Transceiver
There are three types of wireless temperature transceivers, which receive temperature data via radio frequency. The transceiver is matched to different sensor models, and the sensor's transmission distance determines whether the receiving device can receive data from multiple cabinets.
5.3 Acrel Display Terminal
The display device connects to the transceiver via RS485 and can be embedded in the cabinet. If it is inconvenient to drill holes in the cabinet, it can also be wall-mounted in the power distribution room. This allows operators to conveniently monitor the real-time temperature of electrical nodes on-site, and also view the on-site situation in the back-end system via RS485 or Ethernet communication.
6 Application Outlook
From engineering application examples, the substation wireless temperature measurement system demonstrates accurate, stable, and reliable online temperature measurements, and its anti-interference capabilities have passed on-site testing. This system allows for real-time monitoring of the operating status and health level of substation high-voltage equipment, especially high-voltage switchgear, and analysis of equipment condition trends. This is significant for improving equipment operation and maintenance, timely detection of potential hazards, and reducing power outages. Online temperature measurement is applicable not only to sealed high-voltage switchgear but also to open outdoor high-voltage equipment. With the widespread adoption of wireless temperature measurement systems, substation online temperature measurement will gradually replace current manual temperature measurement methods, achieving real-time online temperature monitoring of substation equipment.
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