Integrated cable temperature monitoring system

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I. Background In power systems, there are numerous variable temperatures that need to be monitored throughout the entire transmission process, from power plants to power transmission and distribution equipment, and all the way to the electrical appliances of end users. Ensuring the stable operation of cables is a crucial factor for maintaining continuous and safe power supply. An important parameter determining the stable operation of cables is their insulation performance. Since many high-voltage cables are installed outdoors, various complex factors can lead to failures in these cables, including issues related to the quality of construction, adverse weather conditions, and external damage. Typically, when problems occur in power cables, their temperature rises, which can result in serious faults. An integrated cable temperature monitoring system solution developed by Nanjing Guogao Electrical Automation Co., Ltd. is illustrated through a case study from a petrochemical industry project. This project is located in a city on the eastern coast. The power supply system for the entire project comes from 35kV substations in two different areas; two 10kV power supplies, one as the main source and the other as a backup, are used to supply power to the site. The high-voltage cables are laid over long distances within sea bridges, which constitutes a typical environment with special requirements. The thermal expansion and vibrations associated with these bridges increase the likelihood of failures in the high-voltage cables. To address this issue, through communication with the client and internal analysis, we developed a highly reliable comprehensive solution. The GDTS-4 distributed fiber optic temperature monitoring system provides continuous, long-distance online monitoring of the cable itself. In combination with the GCW-A-9W wireless temperature measurement and centralized display system, it enables real-time dynamic monitoring of the operating conditions of areas where temperature increases may occur, such as high-voltage cable joints and other vulnerable sections. Numerous practical cases have shown that failures in power cables during operation do not occur suddenly; rather, it is a process of gradual change leading to a sudden failure. Therefore, by employing precise and continuous online temperature monitoring, detection systems can identify existing problems in a timely manner and take appropriate actions, thereby preventing the escalation of those failures. Through the combination of points and areas, the comprehensive solution **improves the precision, accuracy, and timeliness of sampling, as well as the reliability of the system. Meanwhile, the advanced fiber-optic temperature sensing technology features high reliability, passive intrinsically safe operation, resistance to electromagnetic interference, corrosion resistance, good temperature tolerance, and a long transmission distance. II. Overview of the Solution 1. Working Principle The GDTS-4 distributed optical fiber temperature online monitoring system is a distributed temperature detection system based on the principle of Raman backscattering and optical time-domain reflection; its principle is shown in Figure 1 below. Figure 1 shows that during the propagation of laser pulses within the fiber, backscattered light is generated. The Stokes and Anti-stokes components of this scattered light are affected by temperature changes, with the Anti-stokes component being particularly sensitive to temperature; other wavelengths, on the other hand, are not affected by temperature changes. When the temperature at a certain point along the optical fiber changes, its intensity changes as well. By accurately measuring the difference in signal strength of the scattered light, the temperature can be measured precisely. By measuring the arrival time of the reflected light pulse, it is possible to determine the location of the temperature reading, similar to how radar echoes are used to show the distance of a car or airplane. 2. Concept of the solution: Due to the specific conditions of the customer’s operational environment, the design plan must take into account factors such as the accuracy of sampling, the precision and timeliness of temperature measurement, the ability to resist various interferences in that environment, as well as issues related to subsequent maintenance. The fiber optic temperature measurement solution enables the acquisition of continuous sampling points along the entire cable, **reducing factors of uncertainty. The temperature-sensing fiber optic cables contain no electrical or moving components, and have a service life of 30 years, which lowers maintenance costs. Temperature data is transmitted via optical signals, offering protection against shock and electromagnetic interference as well as the ability to function in various harsh environments. In conjunction with wireless temperature measurement systems, it is possible to detect faults in joints and other vulnerable areas in a timely and effective manner, thereby increasing the sampling density and enhancing the reliability of the monitoring system. In the comprehensive solution, by establishing data interfaces that enable data exchange with the primary management platform and the secondary remote control platform, and by making these interfaces accessible from outside, it is possible to ensure the interoperability of various types of information within the cable ducts. This leads to high efficiency in information retrieval and high accuracy in alarms, thereby enabling comprehensive monitoring of cable operations. 3. Through communication with the client, the overall solution architecture was developed by taking into account the client’s actual requirements on site; the architecture is shown in Figure 2 below. Figure 2: The GDTS-4 distributed fiber optic temperature monitoring system consists of a distributed fiber optic temperature monitoring host, PC-related peripherals, and temperature-sensing optical cables. To ensure the absolute safety of the cables under monitoring, this system utilizes a state-of-the-art, high-performance linear fiber optic temperature sensing system. The temperature-sensing fibers are installed on the high-voltage cables located in cable trenches and cable passageways, and then connected to the monitoring unit in the control room. Once the monitoring unit demodulates the light signals containing temperature information, it is possible to determine the temperature distribution along the cables. The monitoring host transmits data to the display operating system via a communication port, generating intuitive graphic and textual interfaces for users to view and query. The GCW-A-9W wireless temperature measurement centralized display and monitoring system consists of a server backend and wireless temperature measurement devices. The server backend can be combined with the GDTS-4 backend. The wireless temperature measurement devices are made up of multiple wireless temperature monitoring units and numerous wireless temperature sensors; one such measurement device can connect to up to 240 sensors. At the sensor connections and cable joints, as well as in other vulnerable areas, real-time dynamic monitoring of the operating conditions of areas where temperature rises occur is carried out. The data collected includes temperature, humidity, and operating voltage. The temperature measurement device can transmit this data to a backend server via various communication methods, enabling data analysis to be performed. III. Performance Features 1. The GDTS-4 distributed optical fiber temperature online monitoring system enables real-time monitoring of temperature, allowing for early warnings and prevention of problems before they occur. ◆ High security and reliability: It samples optical wave signals, remaining unaffected by strong electromagnetic interference in high-voltage environments, ensuring stable and reliable data. Furthermore, the fiber optic cable is insulating and non-conductive, which ensures the safety of operators. ◆ Good environmental adaptability: The main component of optical fibers is quartz, which gives them very stable properties; they are resistant to water immersion and acid-base corrosion, with a service life of up to 30 years. Furthermore, optical fibers are bendable, highly flexible, and not prone to breaking, which facilitates construction. With a special outer sheath, it can effectively prevent dust accumulation as well as creepage caused by moisture and humidity. ◆ The system boasts excellent performance: the temperature measurement accuracy is generally 1°C, and the spatial resolution is typically 1 meter ； By configuring appropriate optical switches, it is possible to monitor up to 64 channels simultaneously. ◆ The software offers a wide range of functions: it allows for setting multiple temperature threshold alarms, such as a pre-alarm at 40°C and actions to be taken at 50°C, and these settings can be adjusted according to the conditions of the actual environment ； While setting an over-temperature alarm, it is also possible to set alarms for abnormal temperature rise rates, or combine constant-temperature and differential-temperature alarms. Fire alarm signals can be transmitted through sound and light alerts, relay control, and integration with fire-fighting systems, allowing for appropriate corrective actions to be taken. ◆ Self-check and correction function: The device features real-time self-check capabilities; in the event of an accident such as a break or damage caused by rodents, the system immediately sends out alerts and indicates to the staff where to carry out repairs. The severed fiber can be reconnected using a fiber splicer, allowing it to be used again. In addition, a built-in data correction unit performs real-time correction of the temperature data collected, thereby preventing deviations caused by the aging of the light source over time or other factors. ◆ Compatibility: The system can be interconnected with PCs, fire alarm systems, SCADA, and other control systems via RS232, dry contact, Ethernet, and other means ； 2. GCW-A-9W Wireless Temperature Measurement Centralized Display and Detection System 2.1 The external structure of the wireless temperature monitoring device is shown in Figure 3. The panel displays the following elements: ① Alarm indicator light ② Warning indicator light ③ Operation indicator light ④ Power supply indicator light ⑤ Temperature value display ⑥ Voltage supplied to the temperature sensor display ⑦ Alarm status display ⑧ Clock display. The performance parameters of the product are shown in Figure 4. Figure 4 2.2 Wireless temperature sensors There are various specifications and models of wireless temperature sensors available, which can be selected based on the actual requirements of the installation site. The parameters are described in Figure 5 below. Figure 5-4: Installation of system equipment. 1. Installation of computers and monitoring hosts: Industrial computers, analyzers, and monitors are installed in the monitoring cabinets or control desks in the control room. 2. Installation of the temperature-sensing fiber: Unfold the temperature-sensing fiber along the path of the high-voltage cable being measured, and secure it to the cable using flame-retardant straps. When monitoring multiple high-voltage cables simultaneously, the temperature-sensing optical fiber can be laid in an S shape along the high-voltage cables to increase the coverage area. The installation result is shown in Figure 6. Since the temperature-sensing fiber not only serves as a carrier for signals but also functions as a temperature sensor, the quality of its installation has a direct impact on the accuracy of measurements. Therefore, the following points should be taken into account: The temperature-sensing fiber, just like electrical wires, should be protected from damage or breakage caused by external forces. Thermometry fibers are made of quartz, and when they need to be laid in a bent configuration, this must be done using arcs with a radius greater than 5 cm; otherwise, fiber loss will occur, affecting the accuracy of measurements. Thermometric fiber optic connectors must be kept clean; to this end, the fibers can be laid first and then the connectors installed. 3. Installation of the cable joint section: Since cable joints are areas prone to overheating problems, most cable fires are caused by the heat generated at these joints. If not addressed promptly, it can lead to widespread cable fires that result in significant losses. Therefore, cable joints are also areas that require close monitoring. Bind the wireless temperature sensor to cable connectors or some vulnerable areas. V. On-site acceptance: The time and conditions for on-site acceptance shall be determined by the buyer based on the progress of on-site installation and commissioning. The seller shall complete all tasks related to on-site installation and commissioning, optimize the parameters based on the data obtained from on-site tests to achieve the desired optimal results, and provide training for the buyer’s technical staff so that they can master the skills necessary for system maintenance. After the on-site acceptance tests are completed, both parties will sign to confirm the end of the tests. VI. Technical Training and Services: To facilitate the installation, commissioning, and operation of the equipment, the buyer may assign senior technical personnel to provide services such as installation, commissioning, and startup. In addition to answering and resolving questions raised by the buyer within the scope of the contract, the seller’s technical staff will also provide detailed explanations regarding the drawings, operation methods, equipment settings, and precautions for use. Technical services after the warranty period: After the warranty period ends, the seller will still provide the buyer with preferential services, offering the necessary spare parts at reasonable prices. The seller guarantees that it will be able to supply the spare parts for all the equipment provided under the contract, should there be a need to purchase them again within 5 years.