Summary:An analysis of issues encountered during equipment inspections at rolling steel mills has led to a proposal for using wireless temperature measurement to address inspection challenges. By comparing the technical specifications and advantages of active and passive wireless temperature sensors, passive sensors were installed in high-voltage switchgear cabinets, and active sensors were mounted on crane motors for real-time monitoring. The wireless temperature measurement system has been in operation for nearly a year, significantly enhancing inspection efficiency. However, some issues have been identified during operation, requiring further improvement and refinement to achieve centralized temperature monitoring of the entire factory's wireless temperature measurement system.
Keywords:Wireless Temperature Measuring Device; Wireless Temperature Sensor; Hard-to-Inspect Areas; High-Voltage Vacuum Circuit Breaker; Vehicle Operations
Introduction
The steel rolling plant has four production lines, including: billet production line, high-speed wire production line, billet-wire composite line (dual line for high billet and high wire), and section steel production line. The billet production line has 33 high-voltage cabinets and 15 cranes; the high-speed wire production line has 40 high-voltage cabinets and 19 cranes; the section steel production line has 30 high-voltage cabinets and 16 cranes. In total, there are 103 high-voltage cabinets and 50 cranes. This article discusses the application of wireless temperature measurement devices in switch cabinets, crane motors, and key motors, achieving functions such as temperature control, real-time alarms for vacuum circuit breaker contacts, crane motors, and key equipment motors. This helps to detect and prevent potential hazards in advance, avoiding unexpected damage to critical equipment and preventing incalculable losses.
Issues Encountered During Equipment Inspection
The method for inspecting the main contact of a high-voltage switchgear is to power off, pull out the trolley, and then tighten it and measure the temperature. The inspection cycle is quarterly. However, the degradation of the equipment is non-cyclical and irregular, especially for the main contacts of high-voltage switches, which require real-time monitoring to grasp the degradation trend, detect and address potential hazards in a timely manner. Otherwise, the consequences of any abnormal occurrences are unimaginable. Given the frequent operation of the trolley, it is difficult to perform a comprehensive inspection daily. Using a PT100 temperature measurement element for real-time temperature measurement of the motor is also challenging due to the trolley's need to repeatedly lift steel and steel billets, making it impossible to ensure the safety of the wiring.
2 Analysis of High-Voltage Switchgear and Hoisting Motor Operation
A statistical analysis has been conducted on the abnormal conditions of equipment such as high-voltage switch cabinets and trolley motors that occurred in 2021, details as follows:
On May 19th, during the spring prevention period for steel billets, while tightening the static and dynamic contacts of the high-voltage cabinet, it was discovered that the static contact of the high-voltage distribution cabinet of the No.1 heating furnace had a discoloration.
On July 1st, during the spring anti-frost period of the bar wire production line, while cleaning and tightening the car in the high-voltage cabinet's rolling rectifier cabinet, it was discovered that the moving contact of phase B on the car had a discoloration.
On September 8th, the main hook motor of the No. 1 carriage for steel billet raw materials was damaged due to a missing phase in the stator winding.
On September 24th, the No. 3 pump motor of the type steel medium-pressure water station was damaged due to burnout, which was found to be caused by a failed oil pump motor for the No. 3 pump, leading to the motor operating with insufficient oil and subsequent burnout.
Analysis of the aforementioned four abnormal cases reveals that the inability to effectively observe the contact between moving and stationary contacts, and to check if the bolts of moving and stationary contacts are loose, during the operation of high-voltage switchgear, is the main cause of abnormal contact temperature and discoloration. The daily inspection of driving motors and critical equipment motors has a certain periodicity and cannot be done in real-time. If an abnormal temperature in the motor is not detected and addressed promptly, the motor will be damaged over a period of time.
3 Solutions
After researching, we've decided to employ wireless temperature measurement techniques to address the issues encountered during equipment inspections.
3.1 Selection of Wireless Temperature Sensing Sensors
Active Wireless Temperature Sensing Sensor vs Passive Wireless Temperature Sensing Sensor
A comparison of the characteristics of wireless temperature sensors: Passive wireless temperature sensors are chosen for high-voltage switchgear, while active wireless temperature sensors are used in the temperature monitoring system for trolley motors, due to their long transmission distance and ease of installation.
3.2 Hardware Design and Installation of the Wireless Temperature Measurement System
The entire temperature sensing system consists of three main parts: wireless temperature sensors, an on-site monitoring host, and a backend monitoring system. The wireless temperature sensor module transmits temperature data through radio waves to the wireless temperature sensing concentrator, without any interference or impact on other devices. The wireless temperature sensing concentrator features a wireless communication port, allowing temperature data to be wirelessly uploaded to the backend management system for data analysis and processing. This system then utilizes an output module to implement alarm functions.
3.2.1 High-Voltage Switchgear Wireless Temperature Measurement System
3.2.1.1 Working Principle and Relevant Technical Parameters of Passive Wireless Temperature Sensor
When alternating current flows through a conductor, an induced magnetic core generates an induced current. This current is then processed through a conversion circuit, overvoltage protection circuit, voltage stabilization circuit, and CPU temperature sampling circuit, before being transmitted to the receiving device via a wireless RF module [1-2].
3.2.1.2 Steps for Installing Passive Wireless Temperature Sensors
(1) Expected installation length: Fold the power-taking alloy strip 1-2 times.
(2) Insert the folded power strip into the sensor.
(3) Wrap the module around the main contact of the vacuum circuit breaker, tighten the folded sides of the alloy sheet, and then fold the tail back and secure it.
(4) Wrap the silicone strap around the charging pad and secure it tightly. The module should be tightly adhered to the area being tested.
3.2.1.3 Passive Wireless Temperature Measurement Receiver Host
The touchless wireless temperature measurement master can monitor the working status of wireless temperature sensors, displaying the temperature of the measured contact point, alarm prompts, and outputs in real-time. It connects to an alarm indicator light via the output module.
Upon installation, the system can display the temperature of the tested object and the working voltage of the sensor in real-time, and will output an alarm based on the set alarm values.
3.2.2 Wireless Temperature Measurement System for Vehicle Motors
3.2.2.1 Working Principle of Active Wireless Temperature Sensor and Relevant Technical Parameters
Active temperature sensors are installed on the object being measured. Through sampling filtering circuit, amplification circuit, and wireless transmission circuit, the temperature value is transmitted to the receiving device. It monitors the current temperature of the measured part in real-time, as well as the supply voltage of the sensor itself. All measured data are then wirelessly uploaded to the wireless temperature measurement master unit. Relevant technical parameters are shown in Table 3.
3.2.2.2 Installation of Active Wireless Temperature Sensors
The strap with an active wireless temperature sensor is removed, and the unit is mounted on the body of the motor being measured.
3.2.2.3 Active Wireless Temperature Measurement Receiver Host
The host machine will be installed at the nearest control desk, with an external alarm indicator light connected to the output module. In case of an over-temperature alarm, the indicator light will flash to alert, enabling timely detection of anomalies.
Field Applications and Improvements of 4 Non-Contact Temperature Measurement Systems
On-site installation of a wireless temperature measurement system has been implemented to monitor the temperatures of main contacts in high-voltage switchgear and driving motors in real-time. After a period of use, some over-temperature alarms and potential hazards were promptly detected, and measures were taken to address them, preventing motor damage and major faults in the high-voltage switchgear. This has effectively enhanced the efficiency of the inspection process.
4.1 Preventive Management Effect of Wireless Temperature Measurement System
During the use of the wireless temperature measurement system, some over-temperature alarms were detected.
(1) The rod pump house's precision rolling slurry ring pump motor triggered an overheating alarm. Upon inspection on-site, the motor body temperature was measured at 75°C, and the backup motor was immediately put into use. Inspection of the overheating alarm motor revealed a decrease in insulation resistance, preventing the motor from being damaged by overheating.
(2) The motor of the bar air exhaust unit experienced an over-temperature alarm during operation. Upon on-site inspection, it was found that the cooling fan of the motor was damaged, causing the motor temperature to gradually rise. By switching to a backup unit, production was ensured to continue smoothly.
(3) A high-voltage distribution cabinet for steel bars revealed a temperature of 54℃ in phase B of the busbar contactor. An immediate application for a switch operation was submitted to the upper power supply department. Inspection found that the static contactor had discoloration and loose bolts. After tightening and polishing, it was reinstalled. The next day, the temperature dropped to 38℃, preventing a major accident from occurring in the high-voltage switchgear.
4.2 Improved Non-Contact Temperature Measurement System
The wireless temperature measurement system has been in operation for nearly a year, with corresponding improvements made to issues identified during its operation.
During the transportation of steel billets and steel bars, the wireless temperature sensor signals were somewhat unstable due to varying travel distances. By welding the internal antenna of the sensors to extend it, the transmission distance was increased, ensuring stable signal transmission.
(2) The alarm temperature for the rod material busbar terminal is set at 55°C. Due to the passive wireless temperature sensor being installed on the main terminal sleeve, the measured temperature value deviates significantly from the actual temperature. By replacing it with a miniature passive wireless temperature sensor mounted on the main terminal of the high-voltage switchgear, the contact temperature can be measured more accurately.
4.3 Current Shortcomings in Production and Application
The steel rolling mill has 103 high-voltage cabinets, of which 22 are rectifier transformer high-voltage cabinets. The rectifier transformer is responsible for supplying power to the DC motor, with current only flowing during the rolling process. The power supply method for the passive wireless temperature sensor is by induction current, with communication frequency ranging from 10 to 60 seconds. This means that when there is no rolling workpiece and the DC motor is not in use, the passive wireless temperature sensor cannot sense the main contact temperature. An active wireless temperature sensor is required, which operates through induction temperature sensing. As a result, regardless of whether there is current flowing through the main contact, the temperature of the contact can be displayed in real-time on the temperature measurement host.
(2) The output module of the high-voltage switchgear has been connected to an audible and visual alarm light. It will emit an alarm signal upon overheating. However, it is not connected to the PLC control system, so the signal cannot be displayed on the monitoring screen.
(3) The temperature monitoring for driving motors has been successfully integrated into the temperature measurement host at the nearest control station as scheduled. Only the control station can view the alarms and temperatures. Next, we plan to transmit signals from all control station temperature measurement hosts back to the electrical control room's monitoring computer via fiber optics, achieving centralized temperature monitoring of the entire factory's wireless temperature measurement system.
AnkoRui Online Temperature Monitoring System Solution
5.1 Overview
The electrical contact online temperature measurement device is suitable for monitoring the temperature of cable joints, circuit breaker contacts, knife switches, high-voltage cable mid-sections, dry transformers, and low-voltage high-current equipment within high and low-voltage switchgear cabinets. It prevents potential safety hazards caused by overheating due to oxidation, loosening, dust, and other factors during operation, thereby enhancing equipment safety. It provides timely, continuous, and accurate reflection of the equipment's operating status, reducing the incidence of equipment accidents.
The Acrel-2000T wireless temperature measurement monitoring system communicates directly with equipment at the bay level via RS485 bus or Ethernet. The system design adheres to international standards such as Modbus-RTU, Modbus-TCP, significantly enhancing its security, reliability, and openness. The system features remote signaling, measurement, control, adjustment, configuration, event alarms, trend graphs, bar charts, reports, and user management. It can monitor the operational status of wireless temperature measurement system devices, enabling rapid alarm responses and preventing severe failures.
5.2 Application Locations
Temperature monitoring solutions suitable for power equipment in industrial and mining enterprises such as universal power IoT, steel mills, chemical plants, cement factories, data centers, hospitals, airports, power plants, coal mines, and substation transformer stations.
5.3 System Structure
Temperature Online Monitoring System Diagram
5.4 System Functionality
The Acrel-2000T temperature monitoring system host is installed in the on-duty monitoring room and can remotely monitor the operating temperatures of all switchgear within the system. The system features the following main functions:
- Temperature Display: Shows the real-time values of each temperature measurement point within the power distribution system, and allows for remote data viewing via computer WEB or mobile APP.
- Temperature Trend Curves: View the temperature trend curves for each temperature sensing point.
- Operation Report: Query and print temperature data at various temperature measurement points.
- Real-time Alerts: The system can issue alerts for abnormal temperatures at various temperature sensing points. It features real-time voice alarm capabilities, capable of providing voice alerts for all events, with alert methods including pop-ups and voice alarms. Additionally, it can send alert messages via SMS or APP push notifications, promptly reminding on-duty staff.
- Historical Event Query: Stores and manages records of events like temperature limits, facilitating users to trace historical system events and alarms, enabling query statistics and accident analysis.
References
Peng Yun. Research on Online Temperature Measurement Technology of 10kV High-Voltage Switchgear [D]. Guangzhou: South China University of Technology, 2010.
Zhao Bingcheng. Development and Application of an Online Temperature Measurement System for High-Voltage Switchgear [D]. Hangzhou: Zhejiang University, 2011.
Ma Xiang, Du Jian, Wei Jie, Cheng Mingmin, Li Yubin, Liu Lipeng, Application of Wireless Temperature Measurement System in Equipment Inspection
[4] Ankorri Enterprise Microgrid Design and Application Manual, 2022 May Edition
