How can voltage drop be zero if E-field isn't?

[greypilgrim]

Hi.
I learned that in an ideal conductor in a circuit, the voltage drop is zero. But how does this agree with the basic definition of voltage
$$U_{AB}=\int_A^B \vec{E}\cdot d\vec{s}\enspace ?$$
The electric field inside a conductor only vanishes in static conditions, but in an electric circuit, it makes up the driving force of the current and is obviously nonzero.

 

[vanhees71]

In an ideal conductor you can have a perpetual current without any voltage drop. You don't need to keep the current flowing by an external force since there's no friction. This is realized by superconductors, where you can have currents running for a very long time.

https://en.wikipedia.org/wiki/Persistent_current#Persistent_currents_in_superconductors