FIR modeling of voltage instrument transformers with iron core for the study of fast transients

Modern electronics found in various measuring equipment is sensitive to the effect of transient over-voltages. This paper treats the measurement procedure for the estimation of Finite Impulse Response (FIR) models of voltage instrument transformers, dedicated for the study of fast electromagnetic transients, with the special concern to its influence on the equipment connected to the secondary. A black-box approach is applied, and the model identification is based solely on a single measurement with the impulse excitation. The paper proposes two different procedures for the estimation of the analytical expression of the excitation, based on the parameters of the impulse generator or its estimation using a least-squares procedure. The frequency response of the transformer is used for the design of an initial FIR model, which was further reduced using corrected Akaike information criterion. This way the duration of the transient response calculation is further decreased, and the computation complexity reduced. Once determined, the FIR model allows, through the digital filtering operation (closely related to the concept of recursive convolution), a very easy time-domain calculation of the system's response at any excitation.