Field Transients in Magnetic Systems A Study of Field Transients in Iron Cores Partially Laminated and Partially Solid

The complete mathematical solution of applying suddenly a d-c. voltage to an electromagnetic circuit composed of an electric coil with a partly laminated and partly solid iron core containing an air-gap is presented in this paper. Starting from Maxwell´s field equations for the eddy currents and the magnetic field in the iron core, the solution of the time conditions is reached with the aid of Heaviside´s operational calculus. The result is expressed by means of a time constant of the magnetic field, composed of the time constant of the electric circuit and a fraction of a new-defined time constant of the solid iron part due to the eddy currents in that part. The importance of this result is illustrated by its application to a numerical example and to the effectiveness of quick response excitation in the case of large synchronous generators. Finally some other important applications are discussed.