• Large amount of heat may be produced causing almost instant evaporating of liquid helium and quick rise in temperature of the coil resulting in the damage of the coil and possible explosive build-up of helium gas pressure.
• A high voltage may develop in some sections of the coil which may result in burn out of insulation if the coil.

To avoid the above danger the usual practice is to dump the coil energy quickly in an outside load so that the magnet is quickly de-energized before it is damaged.

The inventors have developed a novel analogue electronic circuit for early sensing of quench initiation in the charged coil which is then used to connect the dump load across the coil draining the coil of its stored energy quickly.

The basic principle of the invention is to compare the voltage drops across different sections of the coil, after bringing them to a common virtual ground and finding the maximum of the differences between the voltages of any two sections and trigger a protective mechanism if the maximum of these differences exceeds a thresh hold value, which can be adjusted externally. The circuit has been built using inexpensive operational amplifiers and diodes and has been found to function very satisfactorily in the protection of a SC coil in a 0.5 MJ SMES system during quench test.