Van de Graff generator?

An insulation conductor means an isolated conductor, i.e. it is not connected to anything, including earth.

When an insulated conductor is placed very close to the charged dome of a van de Graaff generator, the strong electric field established between the conductor and the charged dome will ionize the air in between, producing +ve ions and (-ve charged) free electrons. Assume the generator dome is positively charged, the free electrons will be attracted to the dome, whereas the +ve ions will be repelled towards the conductor.

When the +ve ions touch the conductor surface, their charges will be transferred to the conductor by stripping off electrons from the conductor surface. The +ve ions are then neutralized and the conductor becomes +ve charged due to losing of electrons to the +ve ions. As a result, the conductor is charged with the same sign as the generator dome.

Therefore, charges on the dome do not go directly from the dome to the conductor. It is by an ionization process, with air as a medium, that helps to carry the charges towards the conductor.