There is concern that the levels of inertia in power systems may decrease in future, due to increased levels of energy being provided from renewable sources, which typically have little or no inertia. Voltage Source Converters (VSC) used in high voltage direct current (HVDC) transmission applications are often deliberately controlled in order to de-couple transients to prevent propagation of instability between interconnected systems. However, this can deny much needed support during transients that would otherwise be available from system inertia provided by rotating plant. This paper proposes a novel VSC-HVDC control system termed "INEC" (INertia Emulation Control) which enables a VSC HVDC system to provide support that emulates the inertia of a synchronous generator (SG). The energy to do so comes from the capacitance of the HVDC connection, which may be augmented by the installation of additional capacitance. This paper indicates that the proposed INEC system allows a VSC-HVDC system with a fixed capacitance to emulate a wide range of inertia constants (H) by specifying the amount of permissible DC voltage variation. The proposed INEC scheme has been demonstrated through simulations, and its performance is evaluated for transients that include faults and also changes in load.

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This paper explores the potential future need for fault current er system, and some of the technical implications of this change. It is estimated that approximately 300-400 distribution substations will require fault current limitation, based on the statistical analysis of the projected (or violation). The analysis uses a UK electrical system scenario that satisfies the 2 emissions by 2050. A case study involving the connection of distributed generation (DG) via a superconducting fault current limiter (SFCL) is used to illustrate the potential protection and control issues. In particular, DG fault ride-through, autoreclosure schemes, and transformer inrush current can be problematic for SFCLs that require a recovery period. The potential solutions to these issues are discussed, such as the use of islanding or automation to reduce the fault level.

Fault levels in electrical distribution systems are rising due to the increasing presence of distributed generation (DG) and this rising trend is expected to continue in the future. Superconducting fault current limiters (SFCLs) are a promising solution to this problem. This paper describes factors that govern the selection of the optimal SFCL resistance. The total energy dissipated in an SFCL during a fault is particularly important for estimating the recovery time of the SFCL; the recovery time affects the design, planning, and operation of electrical systems using SFCLs to manage fault levels. Generic equations for the energy dissipation are established, in terms of: fault duration, SFCL resistance, source impedance, source voltage, and fault inception angle. Furthermore, using an analysis that is independent of superconductor material, it is shown that the minimum required volume of superconductor varies linearly with SFCL resistance but, for a given level of fault current limitation and power rating, is independent of system voltage and superconductor resistivity. Hence, there is a compromise between a shorter recovery time, which is desirable, and the cost of the volume of superconducting material needed for the resistance required to achieve a shorter recovery time.

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