The degradation of insulation performance in manganese-zinc materials under high-temperature and high-humidity conditions is the result of the coupled effects of electrical, thermal, hygroscopic, and chemical fields. Its mechanisms can be systematically characterized through four dimensions: microstructural changes, electrical degradation, chemical composition evolution, and environmental adaptability testing.
Microstructural changes are the physical basis for insulation degradation. In high-temperature and high-humidity environments, polar molecules within manganese-zinc materials form hydrogen bonds with water molecules, causing the material to absorb moisture and expand. This expansion disrupts the material's original dense structure, forming micropores or cracks. For example, in epoxy-resin-based manganese-zinc composites exposed to humidity >85% RH, moisture penetrates along grain boundaries or defects, weakening intergranular bonding and causing localized porosity within the material. Furthermore, high temperatures accelerate the thermal motion of molecular chains, distorting the previously stable lattice structure and causing the material to transition from a glassy to a highly elastic state, significantly reducing its mechanical strength.
Electrical degradation directly reflects the degree of insulation degradation. After absorbing moisture, the mobility of conductive ions within the manganese-zinc material increases, forming a continuous water film on the surface, significantly reducing the dielectric strength along the surface. For example, when porcelain insulators are exposed to heat and humidity, the surface water film can reduce the insulation resistance by a factor of 1,000, dropping the power frequency withstand voltage from 42kV to 28kV. Furthermore, water penetration can trigger local discharge, leading to electrical dendrites. Under the influence of an electric field, water molecules migrate along defects in the insulating material, forming microchannels with diameters of approximately 0.1 to 10μm, further weakening the material's dielectric strength.
Chemical composition evolution is an inherent driver of insulation degradation. Under high temperature and humidity, certain components in the manganese-zinc material undergo hydrolysis reactions with water molecules. For example, the ester bonds in epoxy resins easily break under heat and humidity, forming small molecules such as carboxylic acids and alcohols, which increase the material's dielectric loss. Furthermore, the acidic substances produced by hydrolysis can corrode metal inserts or conductive parts, forming electrochemical corrosion cells and accelerating contact failure. Furthermore, microbial growth in heat and humidity can secrete organic acids, further eroding the material surface and forming a bio-aging layer. Environmental adaptability testing is a key tool for quantifying and characterizing degradation patterns. By simulating high-temperature, high-humidity environments (such as 85°C/85% RH), the material aging process can be accelerated. During testing, changes in parameters such as moisture absorption, insulation resistance, and dielectric loss factor should be monitored. For example, after wet-heat aging, the magnetic permeability of manganese-zinc soft magnetic materials decreases due to internal stress release, while eddy current losses increase. Comparing scanning electron microscope (SEM) images of the material before and after aging allows for intuitive observation of grain size changes and crack growth.
Multi-field coupling exacerbates insulation degradation. In high-temperature, high-humidity environments, the superposition of electric, thermal, and humidity fields creates a complex stress state. For example, in areas with significant diurnal temperature fluctuations, the cabinet breathing effect can cause external moisture to penetrate through micro-gaps in the seal, causing the internal humidity to rise by 15% RH within 24 hours. This humidity fluctuation triggers repeated cycles of moisture absorption and drying, accelerating interface aging. Furthermore, local discharges under the influence of the electric field generate ozone and nitrogen oxides, further oxidizing the material surface, creating a vicious cycle.
Protective measures can effectively slow down insulation degradation. Using a multi-layer composite structure (such as a nano-SiO₂ modified layer + a manganese-zinc matrix) can significantly reduce moisture absorption, lowering the insulation layer's water absorption from 0.08% to 0.02%. Furthermore, applying a hydrophobic coating (such as fluorocarbon resin) to the surface can reduce water film formation and increase surface flashover voltage. In terms of structural design, optimizing the sealing ring material and installation process can control the leakage rate to below 1×10⁻⁹Pa·m³/s, effectively preventing moisture infiltration.
The degradation of insulation performance of manganese-zinc materials in high-temperature and high-humidity environments is the result of a synergistic interaction of multiple factors. Microstructural analysis, electrical performance testing, chemical composition testing, and environmental adaptability testing can fully reveal the degradation patterns, providing a scientific basis for material selection, structural optimization, and protective design.
