  We demonstrate the establishment of quantum-secure data transfer links at two
locations in Denmark: on the campus of Technical University of Denmark (DTU) in
Lyngby and between two power grid nodes owned and operated by Energinet in
Odense. Four different channels were investigated, one being a purely
underground fiber and the other three being combinations of underground fibers
and optical ground wires (OPGWs). Coherent `quantum' states at 1550 nm,
prepared and measured using a semi-autonomous continuous-variable quantum key
distribution (CVQKD) prototype, were multiplexed in wavelength with `classical'
100G encrypted data traffic from a pair of commercial layer-2 network
encryption devices operating at around 1300 nm. At DTU, we estimate average
secret key rates in the asymptotic limit of $1.12$ Mbps (channel loss of 5.5 dB
at 1550 nm) while at Energinet, the figures corresponding to the three channels
(with losses of 4.1, 6.7, and 8.9 dB) are $2.05$, $0.90$, and $0.23$ Mbps,
respectively. The demonstration showcases that QKD can serve as an additional
layer to protect sensitive network traffic propagating on insecure channels.
