Definition and digital algorithms of dielectric loss factor for condition monitoring of high voltage power equipment with harmonics emphasis

Experience and applications of the currently available methods for on-line monitoring and diagnostics of high voltage power apparatus is briefly reviewed. Based on the dielectric physics, a new definition of dielectric loss factor with harmonics emphasis is proposed to evaluate the operational conditions of power apparatus on a more reasonable basis, along with corresponding digitised algorithms. Two approaches, namely the decoupling algorithm and the approximating algorithm, are presented to implement the methodologies with the new definition of dielectric loss factor. The impacts of background noise and power frequency fluctuation on estimation accuracy are analysed by computer simulations showing better application qualities of the approximating algorithm than the decoupling one. A comprehensive strategy of simultaneous monitoring of the sum current, dielectric loss factor, resistive current and capacitive current is recommended to give an effective assessment and diagnosis of both the insulation degradation and heat behaviours.