transmission loop. The transmission line is subject to large, sudden load changes due to the operation of a paper mill, with the potential for uncontrolled fluctuations and voltage collapse. The Engineering Test Model is a large SMES with a capacity of approximately 20 MW·h, capable of providing 40 MW of power for 30 minutes or 10 MW of power for 2 hours. System architecture A SMES system typically consists of four parts Superconducting magnet and supporting structure This system includes the superconducting coil, a magnet and the coil protection. Here the energy is stored by disconnecting the coil from the larger system and then using electromagnetic induction from the magnet to induce a current in the superconducting coil. This coil then preserves the current until the coil is reconnected to the larger system, after which the coil partly or fully discharges. Refrigeration system The refrigeration system maintains the superconducting state of the coil by cooling the coil to the operating temperature. Power conditioning system The power conditioning system typically contains a power conversion system that converts DC to AC current and the other way around. Control system The control system monitors the power demand of the grid and controls the power flow from and to the coil. The control system also manages the condition of the SMES coil by controlling the refrigerator. Working principle As a consequence of Faraday’s law of induction, any loop of wire that generates a changing magnetic field in time, also generates an electric field. This process takes energy out of the wire through the electromotive force (EMF). EMF is defined as electromagnetic work done on a unit charge when it has traveled one round of a conductive loop. The energy could now be seen as stored in the electric field. This process uses energy from the wire with power equal to the electric potential times the total charge divided by time. Where Ɛ is the voltage or EMF. By defining the power we can calculate the work which is needed to create such an electric field. Due to energy conservation this amount of work also has to be equal to the energy stored in the field. This formula can be rewritten in the easier to measure variable of electric current by the substitution. Where I is the electric current in Ampere. The EMF Ɛ is an inductance and can thus be rewritten as: Substitution now