Reconstructing Primary Voltages Across Inductive VTs — Part I: Methodology

Inductive voltage transformers (VTs) are the most widely used instrument transformers in power grids operating at 35 kV and below. Frequently, however, during disturbances, the secondary signals are not replicas of the primary voltages because of eddy current effects, capacitive effects, and nonlinearities. In this two-part paper, a new inverse method considering the frequency-dependent characteristics and nonlinearities is proposed to reconstruct the primary voltage from a distorted secondary signal. In Part I, the framework of the method is presented and then realized with two inverse models. An inverse black-box model is used to compensate the eddy currents and capacitive effects, and an inverse duality-derived model is used to consider the nonlinearities. Methods for model parameter determination are described. Experimental validation and analysis of the proposed method are afforded in Part II. The inverse method effectively improves the primary voltage measurement of VTs without any auxiliary high-voltage equipment. The proposed method provides accurate primary voltage waveforms of VTs during disturbances.