Influence of non-sinusoidal voltages on electromechanical stresses in cross-linked polyethylene insulation with micro-defects of power electrical cables

Abstract

Introduction. Power cables with cross-linked polyethylene (XLPE) insulation have significant advantages over traditional oil-filled ones, which have led to their widespread use in high-power electrical networks of all developed countries. However, such cables are increasingly forced to operate under conditions of non-sinusoidal voltages caused by the use of non-linear loads and powerful high-frequency converters of electricity parameters. Problem. Non-sinusoidal voltages and currents in power networks increase nonlinear dielectric losses in XLPE cable insulation, and also intensify the processes of accumulation of space charges (SCs) in the insulation and electromechanical loads near its micro-defects (in particular, water micro-trees) and the occurrence of destructive partial discharges (PDs), which can accelerate the degradation processes of XLPE insulation. All these processes require attention during testing and operation of cables. Goal. To clarify the influence of higher harmonic voltage components on local electric field amplification and Maxwell electromechanical pressures near water micro-inclusions and trees in high-voltage cross-linked polyethylene insulation of power cables. Methodology. The use of the finite element method to determine the dependences of the EF strength distribution, stressed volume, and Maxwell pressure on the geometric characteristics of micro-defects and their location, which affect the EF amplification in XLPE cable insulation under the action of non-sinusoidal power supply voltages. Results. The analysis of the main mechanisms and factors that accelerate the degradation of XLPE cable insulation under the influence of non-sinusoidal voltages has been carried out: an increase in dielectric losses, PDs intensity, distortion of accumulated SCs, acceleration of the development of water trees, the occurrence of higher harmonics and resonant overvoltage. The dependence of the maximum EF strengths and force effects in XLPE cable insulation on the configuration, mutual arrangement and orientation of micro-inclusions relative to the EF was determined. Scientific novelty. The development of the theory of the force influence of non-sinusoidal EF on the electromechanical degradation of the cross-linked polyethylene insulation of power cables based on the establishment of relationships between the configuration features and mutual arrangement of micro-defects and local field amplifications, which leads to an increase in local stressed volumes and Maxwell pressures in the cross-linked polyethylene insulation. Practical value. The obtained results are useful for estimating the stressed volume and Maxwell pressures in the XLPE insulation caused by more complex configurations and mutual arrangement of micro-defects in the insulation of power cables under the influence of non-sinusoidal voltage. References 31, figures 6.