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This paper presents a field-test verified method for continuous tracking of voltage-dependent load model parameters. The basic idea is to use the natural or automatic movement of the under load tap changer (ULTC) as the source of voltage disturbance. Load parameters are estimated from each taping activity. While the idea of using manual ULTC tapping disturbances for load parameter estimation is not new, this paper has demonstrated, through laboratory tests and field measurements, that load parameters can be estimated from the automatic ULTC movements. Since a ULTC often has many movements in any given day, the load parameters can be collected in a consistent, frequent, and predictable manner and, consequently, online estimation and tracking of load parameters becomes feasible. The paper presents the implementation of the proposed method and its field measurement experiences, especially the characteristics of tap movements and the associated load responses. Experiments and a large number of field measurements presented in this paper have shown that the proposed method is a practical and effective method for determining load parameters online.