This article focuses on Poynting’s vector which is defined by a vector product of electric and magnetic fields and plays an important role in considering a flow of electromagnetic energy between power supplies and various types of electromagnetic devices in electrical, electronical and information networks. Poynting’s vector is introduced from a law of energy conservation and its surface integral on an arbitrary domain is equal to the electromagnetic power inside it. This relation can be applied to any system in which there is an interest in the energy flow. Validity of the speculation that Poynting’s vector directly gives the energy flow is examined in various cases. It is pointed out that Poynting’s vector is not equal to the energy flow in some cases. Also discussed is the condition under which the equality holds.
It is important to understand the mechanical behaviors of large-scale SMES (Superconducting Magnetic Energy Storage) when attempting to develop a practical device with high reliability and efficiency. A FEM (Finite Element Method) simulation model developed for determining the nonlinear mechanical deformation of a modified D-shaped elemental coil with a Rutherford-type conductor for a 1kWh/1MW SMES was studied. The model uses nonlinear mechanical characteristics of the conductor measured by a bending test. The nonlinear characteristics of the conductor are roughly explained by the frictional slip between two layers in the conductor. In this paper, a certain coil gap between the conductor and support structure was taken into account for the FEM simulation model in order to examine the mechanical behaviors of the coil in detail. The FEM analysis results for the nonlinear deformation and mechanical loss of the coil were compared to those actually measured in a 1kWh SMES test. The results show a high correlation, which supports the validity of the analysis model.