Before power cables are finalized and used at the factory, long-term cable thermal cycle heating test and high-temperature withstand voltage test are required to test the actual current-carrying parameters of the cable and the temperature stability of the insulation sheath. Conventional cyclic heating testing machines mostly use manual loading of empirical current-carrying values and use PID algorithms to control the temperature of the cable core to achieve a semi-automatic cyclic temperature control process. The real-time nature and overshoot of the control are difficult to effectively restrict, and are easily affected by complex external environment changes, which cannot fully test the actual operation indicators of the cable under test, bringing hidden dangers to the actual operation of the cable product. This project lasted for five years. Supported by the Minhang District Science and Technology Innovation Project, combined with the actual needs of the enterprise, it carried out product technology research and carried out research on power cable cyclic heating test systems and temperature control technology. The project studied the relationship between the heating and temperature rise conditions of the cable core with large delay and the current carrying capacity. Drawing on fuzzy PID technology, a new control method based on the symbol quantity expert system was developed to realize the adaptive control of the system with large time constant delay. The adjustment process achieves stable temperature control under complex environmental conditions in the field, providing a useful new theory, new method and new technology for the field of constant temperature control. This project overcomes the adaptive acquisition technology of the actual value of cable current carrying capacity, realizes automatic real-time measurement of the current carrying capacity of different types of cables in a laboratory environment, realizes dynamic change measurement of cable current carrying capacity in a simulated outfield environment, and provides technical guarantee for the accurate verification of actual operating conditions of cables. This project overcomes the compensation mechanism for geographical environment variables, improves the environmental adaptability of the control system, and realizes constant temperature control for changes in wide environmental conditions. The innovations achieved in the project results are as follows:
(1)An expert base control strategy set based on the symbolic method is proposed. The target operating function is constructed by using the controlled variable, and the execution state of the controlled variable is reflected according to the difference between the controlled variable and the target value. The control process of variable structure parameters is realized through the symbolic method strategy set mapping operation., and the control process of adaptively adjusting the control coefficient is realized; An overshoot suppression mechanism for the target overshoot point is proposed. For the symbol quantity that exceeds the set value, a half-or-doubling adjustment mechanism is adopted to quickly update the parameters of the controlled quantity to meet the control requirements for rapidity and low overshoot of the control process.
(2)A method to extract environmental information from the environment is proposed to identify the latitude and longitude, temperature zone, real-time environmental temperature, humidity, and altitude information of the test site, and revise the control strategy set in the symbol method control expert base to realize the cable cycle in complex field environments. Heating test ensures that the temperature control process is fast and smooth and non-overshoot process.
(3)A thermodynamic model relationship based on the temperature rise curve and actual working conditions is proposed, which solves the temperature rise mechanism of cables with special structures or laying conditions. A thermal path model that considers external environmental changes and dielectric loss in real time is established, realizing the real-time measurement of the current carrying capacity of the cable under working conditions. The process of real-time testing and numerical processing are used to improve the automation and intelligence level of the test equipment.
Through the promotion and application of this project, a knowledge system of 3 invention patent authorizations, 5 utility model patent authorizations, 2 software copyrights, and 6 scientific and technological core papers has been formed, forming a series of product applications that utilize the technology of this project. In the past three years, through the specific implementation of Shanghai Lanbo High Voltage Technology Equipment Co., Ltd., a total of 11.2 million yuan of sales of circulating heating system products have been completed, meeting the inspection needs of cable manufacturers and quality inspection departments for core technical parameters of cables, and improving the thermal cycle test efficiency has promoted the development of large-lag cable temperature control technology and achieved significant economic and social benefits. The products produced have achieved high market share and popularity in the field of power cable testing, providing a strong guarantee for the quality control of power cables in my country.