Why do inductors release a high voltage when disconnected
Changing currents in an inductor result in changes of magnetic flux in the inductor. Then, since the flux changed, the induced voltage changes. That is why

\$v = L{di \over dt} \$

Thus, when you disconnect the inductor, the current changes from whatever it was to 0 in a very short amount of time. The resulting \${di \over dt} \$ becomes very large making the induced voltage very large.