Magnetic Energy Storage in Synchronous Machines

A relation is derived for the magnetic energy storage of a synchronous machine as a function of machine reactances, excitation and terminal voltages. The stored magnetic energy may be represented in terms of a per-unit magnetic energy parameter, having the dimension of seconds, analogous to the representation of stored kinetic energy in terms of the per-unit inertia constant, H. It is found that for most conventional synchronous machines, operating at 60 Hz, the magnitude of the stored magnetic energy is about three decimal orders of magnitude less than the stored kinetic energy.