Superconductors are conductors that have zero resistance and complete flux repulsion effects at a certain temperature. This characteristic sets them apart from all other conductive materials in that they do not lose energy or heat when current flows through them. If superconductors are used to make transformers, generators, motors, current limiters, and energy storage systems, efficient power grids and motors can be realized. Superconducting magnets made from superconducting coils can be used in magnetic resonance imaging and artificially controlled nuclear fusion and other fields. The antimagnetic properties of superconductors also make them an option for magnetic levitation trains.