  Machine learning and computational intelligence technologies gain more and
more popularity as possible solution for issues related to the power grid. One
of these issues, the power flow calculation, is an iterative method to compute
the voltage magnitudes of the power grid's buses from power values. Machine
learning and, especially, artificial neural networks were successfully used as
surrogates for the power flow calculation. Artificial neural networks highly
rely on the quality and size of the training data, but this aspect of the
process is apparently often neglected in the works we found. However, since the
availability of high quality historical data for power grids is limited, we
propose the Correlation Sampling algorithm. We show that this approach is able
to cover a larger area of the sampling space compared to different random
sampling algorithms from the literature and a copula-based approach, while at
the same time inter-dependencies of the inputs are taken into account, which,
from the other algorithms, only the copula-based approach does.
