35kV High Voltage Switchgear Online Temperature Measurement System

Tang Xueyang

Ankerui Electric Co., Ltd. Shanghai Jiading 201801

Abstract:In recent years, with the increasing demand in the electricity market, high-voltage switchgear, as an important component of the power system, has also received attention for its safety and economy. This article focuses on the application of wireless temperature measurement technology in 35kV high-voltage switchgear, introduces the technical characteristics and working principles, summarizes its application in 35kV high-voltage switchgear, and discusses the application of passive wireless temperature measurement systems in substations.

Keywords: High voltage switchgear; Wireless temperature measurement; Technology; application

0 Introduction

With the increasing demand for stable power systems in the electricity market, higher requirements have been put forward for the quality and reliability of power supply. The widespread adoption of new technologies and processes in switchgear has greatly improved its reliability. Sulfur hexafluoride gas has good insulation and arc extinguishing properties, and has been widely used in high-voltage switchgear. The fully enclosed high-voltage switchgear has poor heat dissipation performance under long-term high load, which can easily lead to heat accumulation. The temperature rise will have an adverse effect on the insulation performance of the electrical appliances; The fully enclosed high-voltage switchgear cannot observe the connection between the moving contact and the static contact position inside the cabinet, as well as the opening and closing of the grounding knife switch, and cannot measure the temperature inside the cabinet, which poses a significant safety risk. By directly monitoring the busbar and cable joints of high-voltage switchgear, fires and large-scale power outages caused by overheating can be effectively reduced.

The application significance of wireless temperature measurement technology for high-voltage switchgear

Loose conductive connections in electrical equipment, as well as loose contacts between disconnectors and circuit breakers, can cause temperature accumulation in the equipment, deteriorate the performance of related components, and lead to wire melting and insulation breakdown, seriously endangering the safety of the power grid. With the continuous development of the steel industry, unmanned substations in the power system will be widely used to control various information inside the substations more strictly. However, the temperature monitoring of the main equipment in substations is still in its infancy, with a small monitoring range, especially in the temperature monitoring of enclosed equipment, which is in a "blind spot" and the technical level is relatively backward. Currently, the high-voltage equipment in substations is basically enclosed, and traditional temperature measurement methods are impossible. Some devices also adopt methods such as opening holes and infrared thermometers, but their disadvantage is that they cannot collect and send data in real time, which has high requirements for the insulation performance of the power system; Cannot be directly attached to high-voltage live devices, low accuracy requires inspection, and the effect can only be displayed on site, and is only suitable for exposed equipment; However, the security of this model is higher. Traditional temperature measurement methods cannot meet the real-time monitoring requirements of unmanned stations for key positions of major equipment. Developing a widely applicable, safe and reliable temperature measurement system to monitor the temperature of key parts of important equipment (especially enclosed devices) in real time, detect potential faults in a timely manner, take measures to prevent accidents from further expanding, and is of great significance for ensuring the safe operation of the power grid.

Principles and technical characteristics of several commonly used wireless temperature sensors for 35kV high-voltage switchgear

2.1 Principle of Wireless Temperature Measurement

The basic principles of wireless temperature measurement are: temperature sensors, infrared temperature sensors, semiconductor sensors, surface temperature sensors, and passive wireless sensors. The working principle of a thermal sensor is that the resistance changes with temperature. Thermistors have high sensitivity and can easily detect temperature changes; The disadvantage is that the resistance is non-linear, the temperature range is strict, the components are prone to aging, and the service life is relatively short. As the service life is shortened, the accuracy and stability will also decrease. The characteristic of infrared thermometer is non-contact and does not interfere with the state of the measured object; Its shortcomings lie in its susceptibility to factors such as temperature, humidity, and radiation. Semiconductor sensors have higher accuracy, but compared to thermistors, their response time is slower. The advantages of semiconductor sensors are high safety, high recognition accuracy, and higher reliability. Its characteristic is to use passive temperature measurement and wireless transmission method to measure the temperature of the switchgear. Its advantages are small size and low energy consumption, but its disadvantage is that the signal transmission distance is short, and there should be no obstacles during transmission. If there is displacement or vibration at the measured point, it will cause a change in phase, which will affect the accuracy of temperature measurement. Passive wireless sensors use energy harvesting methods to obtain the energy required by the sensor, eliminating the power supply methods of batteries and conventional CT. The safety and reliability of high-voltage power grids have been achieved through the use of equipotential method. EH technology has the characteristics of cycling and low energy consumption, and is the future development direction of wireless temperature measurement.

2.2 Technical characteristics of temperature measurement

The following are the technical characteristics of passive wireless temperature measurement systems, that is, when the busbar passes through alternating current, an alternating magnetic field will be formed near the busbar, which is usually released into the air and cannot be utilized. Now, a special metal strip is installed on the main row to allow the energy in the magnetic field to flow through the metal strip, and there is a coil on the metal strip. When the current gathers together, the MCU will release enough current, and then use wireless network to transfer heat to the MCU. The sensor uses an AC magnetic field that was previously useless to provide energy to the MCU, allowing it to work for a long time without the use of batteries, with a lifespan of over 10 years and requiring minimal maintenance. Unlike ordinary silicon steel sheets, silicon steel sheets have a straight line, and the primary current and secondary current are linearly related. When the primary current is large, the secondary current will be absorbed by a large amount of secondary current, resulting in the inability to release the secondary current and causing danger. Passive wireless sensors use a special alloy with a small linear range, where the magnetic field quickly reaches saturation and the primary current continues to rise, with almost no increase in current. Therefore, heating equipment is not required, and eddy currents and temperature rise are not generated.

Passive wireless thermometers have a small volume, and after installation, their height and the height of the moving contact iron ring will not have any impact on the insulation distance or the safety of the power device. The signal of the passive wireless sensor needs to be transmitted from the switchgear, which is more than 20 meters away, so there is no receiving device installed in the switchgear, no cable, and no antenna. There is only one sensor, which will not have any impact on electrical safety. At present, most wireless sensing devices in China use high-precision imported digital sensing components, and they all use contact temperature measurement. This sensor can achieve rapid measurement of temperature changes near the hotspot, greatly improving its accuracy. All data transmission programs must undergo inspection, and the detected data will be deleted, so there will be no temperature errors due to transmission. Small in size, it can be installed on moving contacts, stationary contacts, transformer inlet and outlet lines, knife switches, and other parts. It is a form of installation for multiple sensors, providing convenience for construction.

The factory numbers of all sensors are fixed and only need to be matched on the receiving device, without the need for prior coordination or specialized maintenance or replacement. The sensing system uses frequency division multiple access technology, and each sensor communicates using the same frequency band, with a required frequency band of no more than 20 ms. Passive wireless temperature sensors use the same communication architecture as other sensors such as environmental temperature and humidity, live displays, dehumidifiers, displacement sensors, etc., and can share a single receiving device, which facilitates the installation of sensors to collect other physical quantities in the future. At the same time, it also integrates standard interfaces such as MODBUS and 61850, which can achieve communication with other manufacturers. Provide various sharing interfaces for information sharing on other platforms. It has RS485 communication interface, TCP/IP communication interface, and RS232 communication interface. For the convenience of users, there are multiple display interfaces, including separate display interfaces for switchgear and substations, and the ability to centralize data from the entire province on servers. Passive wireless thermometers overcome the disadvantage of insufficient battery power and provide more electricity, so data transmission can be carried out even at higher temperatures. The temperature range is -45~125 degrees Celsius, and manufacturers are still constantly improving. The future temperature will be between -45~135 degrees Celsius.

Application of Passive Wireless Temperature Measurement Technology in 35kV High Voltage Switchgear

To improve the maintenance work of the substation and promptly solve the heating problem of the high-voltage switchgear, a wireless temperature measurement system was selected. According to relevant regulations, combined with actual conditions, on-site debugging and testing were carried out on the 35 kV high-voltage switchgear, data was collected and analyzed, and the reliability and practicality of the system were verified. After adopting wireless temperature measurement technology, the substation effectively controls the heating problem of the 35 kV high-voltage switchgear, ensuring power supply safety.

4 Ankerui wireless temperature measurement system

4.1 System Structure

The Acrel-2000T wireless temperature monitoring system communicates directly with devices in the interval layer through RS485 bus or Ethernet. The system design follows international standards such as Modbus RTU and Modbus TCP transmission protocols, greatly improving safety, reliability, and openness. The system has functions such as remote signaling, telemetry, remote control, remote adjustment, remote setting, event alarm, curve, bar chart, report, and user management. It can monitor the operation status of wireless temperature measurement system equipment, achieve rapid alarm response, and prevent serious faults from occurring.

Suitable for temperature monitoring of power equipment in ubiquitous power Internet of Things, steel mills, chemical, cement, hospitals, airports, power plants, coal mines and other industrial enterprises, as well as substations and distribution stations.

Structure diagram of temperature online monitoring system

4.2 System Functions

The temperature measurement system host Acrel-2000T is installed in the duty monitoring room and can remotely monitor the operating temperature status of all switchgear in the system. The system has the following main functions:

1. Temperature display: Display real-time values of each temperature measurement point in the power distribution system, and also enable remote viewing of data through computer WEB/mobile APP.

1. Temperature curve: View the temperature trend curve of each temperature measurement point.

Run report: query and print temperature data for each temperature measurement point at different times.

Real time alarm: The system can issue alarms for abnormal temperatures at various temperature measurement points. The system has real-time voice alarm function, which can issue voice alarms for all events. The alarm methods include pop ups, voice alarms, etc. It can also push alarm messages through SMS/APP to remind duty personnel in a timely manner.

Historical event query: It can store and manage event records such as temperature exceeding limits, facilitating users to trace the history of system events and alarms, query statistics, accident analysis, etc.

4.3 System Hardware Configuration

The online temperature monitoring system is mainly composed of the temperature sensor and temperature acquisition/display unit on the equipment layer, the edge computing gateway on the communication layer and the host of the temperature measurement system on the station control layer, to realize the online temperature monitoring of key electrical parts of the power transformation and distribution system.

5 Conclusion

Summarized that the current 35kV high-voltage switchgear cannot meet the requirements using conventional wireless temperature measurement technology. High voltage switchgear is a critical equipment in the power system, and if it malfunctions, it will have a significant impact. The 35 kV high-voltage switchgear uses wireless temperature measurement technology for measurement, and the installation of measuring equipment is convenient and the measurement results are fast, which is more in line with the rapid development of technology today. In future temperature measurement technologies, it is necessary to summarize and study the problems that arise during use based on actual application conditions, and improve the temperature measurement system through continuous learning and exploration.

35kV High Voltage Switchgear Online Temperature Measurement System

35kV High Voltage Switchgear Online Temperature Measurement System