STUDY OF SCREENS FOR SUPERCONDUCTING A.C. MACHINES. PART A: SIMPLIFIED DETERMINATION OF TIME CONSTANTS FOR SCREENS OF SUPERCONDUCTING MACHINES

Abstract The transcendental equation whose solutions allow the computation of the exact electromagnetic time constants of a screen surrounded by a shield is at first derived. Then the use of Taylor and asymptotic expansions of the Bessel functions yields approximate expressions for the time constants. Numerical comparison between exact and approximate values shows the validity of the proposed method. Finally, a comparison of the frequency response curves obtained by the F.F.T. method [15] and by our method shows that the approximations lead to satisfactory results.