  Stochastic feed-in of fluctuating renewable energies is steadily increasing
in modern electricity grids and this becomes an important risk factor for
maintaining power grid stability. Here we study the impact of wind power
feed-in on the short-term frequency fluctuations in power grids based on an
IEEE test grid structure, the swing equation for the dynamics of voltage phase
angles, and a series of measured wind speed data. External control measures are
accounted for by adjusting the grid state to the average power feed-in on a
time scale of one minute. The wind power is injected at a single node by
replacing one of the conventional generator nodes in the test grid by a wind
farm. We determine histograms of local frequencies for a large number of
one-minute wind speed sequences taken from the measured data and for different
injection nodes. These histograms exhibit a common type of shape, which can be
described by a Gaussian distribution for small frequencies and a nearly
exponentially decaying tail part. Non-Gaussian features become particularly
pronounced for wind power injection at locations, which are weakly connected to
the main grid structure. This effect is only present when taking into account
the heterogeneities in transmission line and node properties of the grid, while
it disappears upon homogenizing of these features. The standard deviation of
the frequency fluctuations increases linearly with the average injected wind
power.
