Method of investigating thermal fluctuation processes in problems of diagnostics and prediction of insulating materials

Introduction. The investigation of thermal fluctuation processes in insulating materials in accordance with the thermal conductivity theory for solving the problems on diagnostics and forecasting the residual life of insulating materials on the basis of a digital recorder, as well as on the nondestructive temperature method, is described. The work objective is to improve the nondestructive diagnostics methods, namely, the development of an automated control system for the state of insulation, and a computational and experimental study. Materials and Methods. Mathematical models that describe the layer-by-layer temperature distribution of the cable line in accordance with the theory of thermal conductivity using Fourier differential equation are proposed. A generalized algorithm for the operation of the PCL parameters monitoring recorder is created. It implements the technique of nondestructive testing of thermal fluctuation processes in PCL insulation materials. A comparative analysis of the experimental and calculated characteristics of the temperature distributions is carried out. At that, different charging modes of operation and functions of the cable current variation are investigated. Research Results. Mathematical models and software for numerical simulation of the temperature field in the cable cross-section in accordance with the theory of thermal conductivity are developed. Physical properties of materials and the geometric dimensions of cable elements are considered. A comparative analysis of the experimental and calculated characteristics of the temperature distributions is made. The developed simplified mathematical model for determining the temperature of the most heated point of the cable core insulation on the basis of the measured values of the surface temperature of the power cable and the air temperature for various changes in the effective value of the cable current is validated. A method for investigating thermal fluctuation processes based on the layered temperature sensors in PCL is developed and justified. That makes it possible to combine two control techniques - prediction of the growing insulation defect and nondestructive testing of the thermal fluctuation processes of a power cable - in one measuring tool. The suggested mathematical model can be used as a base for calculating the thermal processes of power cables in real time mode, as its adequacy is confirmed by the experimental studies. Discussion and Conclusions. The obtained results can be used in the development of the theory, methods of diagnostics and prediction of the insulating materials state in complex distributed systems under various operating conditions.