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.

No abstract

Distribution networks are evolving towards the vision of smart grids, with increasing penetration of Distributed Generation (DG), introduction of Active Network Management (ANM) and potentially islanded modes of operation. These changes affect both fault levels and fault current paths and have been demonstrated to compromise the correct operation of the overcurrent protection system. This paper presents an adaptive overcurrent protection system which automatically amends the protection settings of all overcurrent relays in response to the impact of DG, ANM and islanding operation. The scheme has been developed using commercially available protection devices, employs IEC61850 based communications and has been demonstrated and tested using a Hardware-In-the-Loop (HIL) laboratory facility. A systematic comparison of the performance of the proposed adaptive scheme alongside that of a conventional overcurrent scheme is presented. This comparison quantifies the decrease in false operations and the reduction of mean operating time that the adaptive system offers.

This paper presents a method for rapid detection of faults on VSC multi-terminal HVDC transmission networks using multi-point optical current sensing. The proposed method uses differential protection as a guiding principle, and is implemented using current measurements obtained from optical current sensors distributed along the transmission line. Performance is assessed through detailed transient simulation using Matlab/Simulink R models, integrating inductive DC-line terminations, detailed DC circuit breaker models and a network of fiber-optic current sensors. Moreover, the feasibility and required performance of optical-based measurements is validated through laboratory testing. Simulation results demonstrate that the proposed protection algorithm can effectively, and within very short period of time, discriminate between faults on the protected line (internal faults), and those occurring on adjacent lines or busbars (external faults). Hardware tests prove that the scheme can be achieved with the existing, available sensing technology.

No abstract