Definition of Instantaneous Dielectric Loss Factor and Digital Algorithm for Online Monitoring

Among the digital algorithms currently available for online monitoring of the dielectric loss factor of power apparatus, there are unavoidable limitations, such as that most of them must strictly meet the synchronous sampling criterion simultaneously with a precondition that the power frequency must be invariable in the sampling periods. This paper presents a unique definition and a corresponding digital algorithm of the instantaneous dielectric loss factor. The theoretical basis of the algorithm is also deduced. In a nonstationary signal environment where power frequencies are randomly variable, the algorithm can accurately track the instantaneous frequency of power signals, recursively calculate the parameters of parallel equivalent circuit, and, finally, figure out the waveform of the instantaneous dielectric loss factor. Simulations and experimental results show that the proposed algorithm renders good application performance without being affected by the limitations incurred from synchronous sampling and harmonics.