  Based on a study of the thermophysical properties, we derived a practical
formula for the normal zone propagation velocity appropriate for
REBa$_2$Cu$_3$O$_{7-x}$ coated conductors in high magnetic fields. An
analytical expression to evaluate the current sharing temperature as a function
of the operating conditions is also proposed. The presented study has allowed
us to account for experimental results not fully understood in the framework of
the models widely used in the literature. In particular, we provided a
fundamental understanding of the experimental evidence that the normal zone
propagation velocity in REBa$_2$Cu$_3$O$_{7-x}$ coated conductors can be mainly
determined by the operating current, regardless of the applied field and
temperature.
