  To address the challenges that the decarbonization of the energy sector is
bringing about, advanced distribution network management and operation
strategies are being developed. Many of these strategies require accurate
network models to work effectively. However, distribution network data are
known to contain errors, and attention has been given to techniques that allow
to derive improved network information. This paper presents a novel method to
derive line impedance values from smart meter measurement time series, with
realistic assumptions in terms of meter accuracy, resolution and penetration.
The method is based on unbalanced state estimation and is cast as a non-convex
quadratically constrained optimization problem. Both line lengths and impedance
matrix models can be estimated based on an exact nonlinear formulation of the
steady-state three-phase network physics. The method is evaluated on the IEEE
European Low Voltage feeder (906 buses) and shows promising results.
