Working Principle Of Paper-Sheathed Wire: Electric Field And Thermal Management Mechanism Of Oil-Paper Composite Insulation

As a key winding material for high-voltage power equipment and high-power motors, the working principle of paper-sheathed wire is based on the synergistic mechanism of current transmission by the metallic conductor and the suppression of electric field concentration and delay of thermal aging by the paper-oil composite insulation system. During operation, paper-sheathed wire not only bears high current loads but also needs to maintain long-term reliable electrical insulation and thermal stability in oil-immersed or sealed environments. Its working mechanism can be explained from two aspects: conductivity transmission and insulation protection.

At the conductivity transmission level, the core of the paper-sheathed wire is a conductor made of highly conductive copper or aluminum. When the equipment is energized, alternating or direct current is evenly distributed along the conductor's cross-section, realizing the transfer of energy from the power source side to the load side. The choice of conductor cross-sectional area and material determines its current-carrying capacity and the level of Joule heating under operating conditions, which is the starting point for the thermal management mechanism design.

At the insulation protection level, the insulation layer of the paper-sheathed wire consists of specially treated electrical insulating paper tightly wrapped around the conductor surface. The insulating paper is made of refined plant fibers and has excellent dielectric strength and mechanical toughness. When used alone, while the paper layer can block current leakage, it is prone to partial discharge under high-voltage conditions due to air gaps or moisture. Therefore, the paper layer needs to be impregnated with mineral or synthetic insulating oil. The oil penetrates the micropores of the paper and removes air, forming an oil-paper composite insulation system.

The working principle of the oil-paper composite structure lies in utilizing the complementary properties of the two media: the high dielectric constant and fluidity of the insulating oil help to distribute the electric field evenly and remove local heat; the insulating paper provides stable mechanical support and a dielectric barrier, inhibiting the formation of discharge channels caused by impurities in the oil. Under AC high voltage, the electric field is mainly distributed in the oil layer, while the paper layer acts as a voltage divider and prevents surface discharge. In DC or pulsed fields, the volume resistivity of the paper can delay charge accumulation and reduce the peak value of the local field strength.

In terms of thermal management, the Joule heat generated during the operation of the paper-insulated wire is conducted to the paper layer through the conductor, and then dissipated to the equipment oil tank or cooling system through the convection and conduction of the impregnating oil. The oil-paper system maintains stable performance within a suitable temperature range, preventing insulation degradation caused by thermal decomposition of the paper layer or volatilization of the impregnating agent.

In general, the working principle of paper-insulated wire is to efficiently conduct electricity through a metallic conductor, and to achieve electric field homogenization, heat dissipation, and mechanical buffering through an oil-paper composite insulation system. This allows it to maintain long-term reliable insulation and operational performance in high-voltage, high-temperature, and oil-immersed environments, providing a fundamental guarantee for the safe operation of large-scale power and industrial equipment.