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This paper presents a new centralized adaptive underfrequency load shedding controller that is integrated with a distribution state estimator to improve the frequency stability of islanded microgrids. While underfrequency load shedding is a well-established corrective emergency frequency-control action, it is not entirely suitable for use in microgrids with low inertia and a limited number of measurement devices. The novel centralized controller presented in this paper overcomes these challenges by incorporating a distribution state estimator to estimate the power consumption of the demand. In parallel to this, the actual active power imbalance in the microgrid is estimated by simultaneously monitoring the system frequency and its rate of change. The centralized controller uses these two variables to determine the correct amount of load to be shed. The performance of the proposed controller has been validated using computer simulations of the actual distribution network in Malaysia. These simulation results show the effectiveness of the proposed centralized controller for preventing power system instabilities, which might lead to cascading outages and even a complete blackout in microgrids that have been disconnected/islanded, from the main grid. [ABSTRACT FROM AUTHOR]

The presence of cavity in motor insulation fed by variable speed drive is one of the sources of partial discharge (PD) occurrence, especially under impulse voltage. This is a serious problem as PD can accelerate degradation of the motor insulation. Therefore, it is important to prevent void discharges from occurring in motor insulation under impulse voltage. In this work, the characteristics of void discharges within dielectric insulation material under impulse voltage were investigated through experiment and modeling. The test object consists of a rectangular void within a polyethylene material. The test object was stressed with different peak magnitude, front time and tail time of the applied impulse voltage. The experimental results were reproduced by simulation results from a void discharge model in insulation material. From the model that was developed, a better understanding on physical parameters that influence the characteristics of void discharges within dielectric material under impulse voltage can be attained. [ABSTRACT FROM PUBLISHER]

The frequency of power system is very sensitive to load changing when operating in islanded mode. This may causes overloading or loss of generation cases. Under-Frequency Load Shedding (UFLS) Scheme is commonly applied to stabilize the frequency during these cases. Conventional UFLS scheme operates successfully in interconnected grid system and may not work well when applied to DG based system operating in islanded mode. This paper presents a new fuzzy logic based under- frequency load shedding scheme implemented on mini hydro type-DG operating in islanded mode. The proposed strategy is based on frequency, rate of change of frequency and load prioritization. In proposed UFLS scheme, a fuzzy logic load shedding controller (FLLSC) with Load Shed Controller Module (LSCM) is modelled. FLLSC measures amount of load to be shed and LSCM shed the respective load to stabilize frequency. The proposed scheme is validated on different event-based and response-based cases. Simulation results show that proposed scheme is effective in shedding optimal number of loads while stabilizing the frequency. [ABSTRACT FROM AUTHOR]

Highlights: [•] Optimal BSS placement reduces the impacts to distribution system performance. [•] The analytical method gave results similar to ABC for optimal BSS placement. [•] ABC gave faster solution in solving BSS sizing cases. [•] Simultaneous BSS and DG Sizing gave the lowest total DG capacity and power loss. [Copyright &y& Elsevier]

Abstract: Under-Frequency Load Shedding (UFLS) is a common technique to maintain power system stability by removing the overload in some part of the system. The existing UFLS schemes operate successfully in the interconnected grid system. A particular approach of UFLS scheme is required for an islanded system which is known to be not as strong as the grid. This paper presents a new approach of UFLS scheme for the implementation in an islanded distribution system. The scheme is based on a combination of adaptive and intelligent techniques. The disturbance magnitude for response based and event based is treated differently: (1) event based is based on the power imbalance and (2) response based is based on the swing equation which relies on the frequency and rate of change of frequency measurement. Dynamic simulation on an intentional islanding operation is performed on an existing Malaysian network interconnected with a mini hydro generation. The objective is to investigate the effectiveness of the proposed scheme. The simulation results demonstrate that the proposed scheme is capable of improving the frequency response of the islanded system. A significant finding is that the scheme can successfully reduce the effect of power deficiency following the grid connected to islanding operation transition. [Copyright &y& Elsevier]

Highlights: [•] Study on directional over-current and earth-fault for biomass micro grid. [•] The delta side of the transformer cannot be cleared by earth-fault relay for single phase to earth fault. [•] Under voltage relay is adopted at the delta side of the transformer. [•] Simulation shows good coordination at all possible locations. [Copyright &y& Elsevier]