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Fault current studies are often required to determine the proper settings for the overcurrent relays. The conventional synchronous generators are known to exhibit high current magnitude during fault, which present an ideal scenario for fault isolation using the cost-effective overcurrent relays. On the other hand, the fault current magnitude from renewable based generation such as solar photovoltaic (PV) is intentionally limited due to the constraints in the power electronic components. Therefore, dispute pertaining to the feasibility of overcurrent relay in inverter based distributed generations (IBDG) applications arises. These disputes mainly arise due to the unavailability of firm understanding of the fault current characteristics from the IBDGs. The problem is further compounded with the availability of numerous possible fault current controls, where various fault current characteristics can be obtained from the IBDGs. In light of this problem, this paper aims to establish the various possible IBDG fault current characteristics, with special attention paid to compliance to the latest grid codes requirements such as low voltage ride through (LVRT) with reactive current injection (RCI). Five different types of RCI controls are analyzed as follows: variable active current control, constant active power control, constant reactive power control, constant active current control, and maximum current control. From the established fault current characteristics in this paper, the disputes pertaining to the feasibility of overcurrent relay for IBDG applications can be resolved and the suitable types of RCI control that allow satisfactory performance of overcurrent relays can be identified. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new approach for optimum simultaneous multi-DG (distributed generation) placement and sizing based on maximization of system loadability without violating the system constraints. DG penetration level, line limit and voltage magnitudes are considered as system constraints. HPSO (hybrid particle swarm optimization) algorithm is also proposed in this paper to find the optimum solution considering maximization of system loadability and the corresponding minimum power losses. The proposed method is tested on standard 16-bus, 33-bus and 69-bus radial distribution test systems. This paper will also compare the proposed method with existing Ettehadi method and present the effectiveness of the proposed method in terms of reduction in power system losses, maximization of system loadability and voltage quality improvement. [Copyright &y& Elsevier]

Highlights: • A new algorithm is proposed for optimum DG placement and sizing.• I 2 R losses minimization and voltage stability maximization is considered in fitness function.• Bus voltage stability and line stability is considered in voltage stability maximization.• Multi-objective PSO is used to solve the problem.• Proposed method is compared with analytical and grid search algorithm. [Copyright &y& Elsevier]

Islanding operation in a distribution network connected to Distributed Generations (DGs) has the advantage of being able to continuously supply power to the loads even when disconnected from the grid. However, there are technical issues that need to be solved in order to guarantee a successful islanding operation. The main challenge in the successful islanding operation is to ensure the stability of frequency and voltage of the distribution system. Commonly load shedding schemes are used as a mechanism to stabilize the magnitude of the frequency and the voltage by shedding some of the loads to ensure an adequate balance between generation and loads. This paper reviews recent load shedding schemes focusing on distribution system application. Their respective merits and demerits are presented. Moreover, this paper also highlights the application of Voltage Stability (VS) index for load shedding schemes. A brief overview of the DG with their respective advantages also presented at the beginning of this paper. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a new algorithm for Distributed Generator (DG) placement and sizing for distribution systems based on a novel index. The index is developed considering stable node voltages referred as power stability index (PSI). A new analytical approach is adopted to visualize the impact of DG on system losses, voltage profile and voltage stability. The proposed algorithm is tested on 12-bus, modified 12-bus and 69-bus radial distribution networks. The test results are also compared and found to be in close agreement with the existing Golden Section Search (GSS) algorithm. [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]