Effects of electrothermal ageing on dielectric performance of metallised biaxial orientation polypropylene film capacitors in strong magnetic fields

The dielectric performance of the pristine and the electrothermal-aged metallised polypropylene capacitors are investigated under different magnetic fields. The energy storage capacity decreases under the magnetic field. At 12 T, the capacitance value of the pristine capacitors decreases by 8.4%-17% and that of the aged capacitors declines by 15%-20%. The dielectric loss is reduced by 2.6%-6.3%, but the equivalent series resistance shows an 8.3%-23.1% growth. The leakage conductivity increases to 202%-354%, which leads to a weakened voltage holding capacity. In addition to the effects of the magnetic fields, the impacts of ageing have also been investigated. The effects of the magnetic field and ageing on the electrical parameters of the capacitors are discussed separately. The molecular chains of the dielectric are oxidised and decomposed during the ageing process, which reduces the insulating properties of the dielectric. The magnetic field inhibits polarisation by changing the polarisation behaviour through Lorentz force and excites the electrons to enhance charge transmission.