  Dynamical simulation of the cascade failures on the EU and USA high-voltage
power grids has been done via solving the second-order Kuramoto equation. We
show that synchronization transition happens by increasing the global coupling
parameter $K$ with metasatble states depending on the initial conditions so
that hysteresis loops occur. We provide analytic results for the time
dependence of frequency spread in the large $K$ approximation and by comparing
it with numerics of $d=2,3$ lattices, we find agreement in the case of ordered
initial conditions. However, different power-law (PL) tails occur, when the
fluctuations are strong. After thermalizing the systems we allow a single line
cut failure and follow the subsequent overloads with respect to threshold
values $T$. The PDFs $p(N_f)$ of the cascade failures exhibit PL tails near the
synchronization transition point $K_c$. Near $K_c$ the exponents of the PL-s
for the US power grid vary with $T$ as $1.4 \le \tau \le 2.1$, in agreement
with the empirical blackout statistics, while on the EU power grid we find
somewhat steeper PL-s characterized by $1.4 \le \tau \le 2.4$. Below $K_c$ we
find signatures of $T$-dependent PL-s, caused by frustrated synchronization,
reminiscent of Griffiths effects. Here we also observe stability growth
following the blackout cascades, similar to intentional islanding, but for $K >
K_c$ this does not happen. For $T < T_c$, bumps appear in the PDFs with large
mean values, known as "dragon king" blackout events. We also analyze the
delaying/stabilizing effects of instantaneous feedback or increased dissipation
and show how local synchronization behaves on geographic maps.
