Abstract-The rapid increase in installed distributed generation (DG) has led to concerns about the impact on the proper operation of the protection system. In particular, the limited fault current capability of inverter interfaced distributed generation (IIDG) could lead to malfunctioning of the distribution network protection system which largely relies on overcurrent based protection techniques. The absence of tried and tested models and methods to calculate the inverter fault current contribution has been a significant challenge to the introduction of IIDG. This paper shows that with a few subtle changes, conventional analytical network analysis techniques can be used to analyse the fault response of inverter dominated distribution networks. The theoretical results are validated by PSCAD simulations and experimental results.

The ever increasing penetration depth of Distribution Energy Resources (DER) and the development of power electronics devices have a significant impact on the development of DC power transmission and distribution systems. This paper provides an overview of the recent advancement and also envisioned research and development on DC grids, with the objective of identification and discussion of the corresponding issues. Brief descriptions of DC grids at various voltage levels and their benefits are presented and discussed. Different layouts for the DC grids are presented and the associated technical issues are highlighted.

Abstruct-In both electrostatic and magnetostatic finite element analysis the need occasionally arises for the inclusion of isolated perfect electric and magnetic conductors, respectively. The surfaces of such conductoss represent equipotentials but do not constitute a Dirichlet boundary condition. Existing methods for constraining such surface potentials to be constant, without giving specific values, are fairly complicated. This paper presents a simple approach which requires no modifications to existing finite element programs that can solve Laplace's and Poisson's equation subject to the usual Dirichlet and Neumann boundary conditions. The paper also addresses the dual problem of voids in conductors and shows how the floatang potential concept can be exploited to obtain streamlines of current flow.

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