  This article presents a tool for the detection of non-technical losses, which
is being developed within the European INTERPRETER project. The tool employs a
hybrid method based on feature detection from smart meter data and grid model
analysis. This paper focuses on the grid model analysis, where voltage
deviations between the grid model (digital twin) and real-world measurements at
a low-voltage pilot site have been evaluated. Energy measurements from smart
meters represent hourly mean power, while voltage measurements are
instantaneous with uneven time intervals. Thus, measurements are not
synchronous, which poses a major challenge for grid analysis. The proposed
method focuses on daily mean, minimum, and maximum voltage and results show
that deviations in daily minimum voltage are the most useful ones. A heatmap is
developed, which helps the DSO expert to have a quick overview of all
deviations of all meters in a certain time interval (1-day time step). A total
of 6 locations have been identified where field inspections will be done.
