Electrodynamic Forces between Electrical Conductors and Cylindrical Magnetic Shields
Milan ` Mišić *
Higher Technical Professional School in Zvečan, Nušićeva 6, 38227, Zvečan, Kosovo under Resolution 1244 UN, Serbia.
Zorica Bogićević
Higher Technical Professional School in Zvečan, Nušićeva 6, 38227, Zvečan, Kosovo under Resolution 1244 UN, Serbia.
Slobodan Bjelić
Faculty of Technical Sciences, University of Priština, Kneza Miloša 7, 38220 Kosovka Mitrovica, Kosovo under Resolution 1244 UN, Serbia.
*Author to whom correspondence should be addressed.
Abstract
Aims: This paper demonstrates a method for calculating electrodynamics stress in single-phase and three-phase isolated conductors. Conductors are coated with a cylindrical shield made out of the material containing a magnetic parameter. Special emphasis is placed on induced eddy current of a shield and its effect on reduction of electrodynamics stress of three-phase conductors.
Methodology: The paper starts with the assumption that the cylindrical structure of the conductor shield is infinitely long σ=0. Inside and outside the shield applies Laplace differential equation for the magnetic vector potential [1,3]. Short circuit currents flow through the three eccentric positioned conductors and create magnetic induction or fluxes in a cylindrical shield. AC power corresponds to the time-varying resulting flux that induces eddy currents in the cylinder. Needed values of induction and fluxes relevant to eddy currents and electrodynamics forces can be determined by a method which is based on the calculation of the magnetic vector potentials and Poisson differential equation, A=µJ [2,4,5]. This procedure requires the establishment of a large number of boundary conditions and taking into account the superposition of multiphase conductive structure values. The impact measure of eddy currents in such an eccentric three-phase structure can be determined by using a similar simple procedure which one of the authors applied in the [6-17].
Conclusion: Electrodynamics forces, according to relationship (32), are significantly lower in shields which encompass only one phase of a conductor due to a protective effect of a shield. Eddy currents, as is demonstrated in this paper, significantly reduce magnetic field intensity produced by currents in conductors. Due to this effect, main electrodynamics forces in one-phase structures with shields, don`t affect the conductor but only affect the shield.
Keywords: Magnetic flux, eddy currents, conductor, electro-dynamic forces, enclosure.