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The microgrid concept is a promising approach for injecting clean, renewable, and reliable electricity into power systems. It can operate in both the grid-connected and the islanding mode. This paper addresses the two main challenges associated with the operation of a microgrid i.e. control and protection. A control strategy for inverter based distributed generation (DG) and an energy storage system (ESS) are proposed to control both the voltage and frequency during islanding operation. The protection scheme is proposed to protect the lines, DG and ESS. Further, the control scheme and the protection scheme are coordinated to avoid nuisance tripping of the DG, ESS and loads. The feasibility of the proposed method is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach based on the loci of instantaneous symmetrical components called "Wing Shape" which requires the measurement of three input stator currents and voltages to diagnose interturn insulation faults in three phase induction motors operating under different loading conditions. In this methodology, the effect of unbalanced supply conditions, constructional imbalances and measurement errors are also investigated. The sizes of the wings determine the loading on the motor and the travel of the wings while their areas determine the degree of severity of the faults. This approach is also applied to detect open circuit faults or single phasing conditions in induction motors. In order to validate this method, experimental results are presented for a 5 hp squirrel cage induction motor. The proposed technique helps improve the reliability, efficiency, and safety of the motor system and industrial plant. It also allows maintenance to be performed in a more efficient manner, since the course of action can be determined based on the type and severity of the fault. [ABSTRACT FROM AUTHOR]

The high probability of a rotor winding failure in a three-phase wound rotor induction motor (WRIM) due to the complicated structure of the rotor necessitates developing efficient techniques for detecting rotor winding faults in their evolving stages. FFT-based motor current signature analysis (MCSA) is extensively used to detect the electric failures of rotors. However, it is complemented by implementing alternative techniques to prevent the failure indicated by the MCSA. Rotor current-based fault detection schemes have been scarcely investigated and implemented in industry. However, this experimental study investigates the rotor winding inter-turn short-circuit (ITSC) faults in a WRIM based on the loci of the symmetrical components of the three-phase rotor currents £ (ir1–ir2) that form a 'Wing Shape.' Hence, the technique is called the 'Wing Technique.' The proposed fault-sensitive and noninvasive approach investigated the effects of unbalanced stator voltages, constructional imbalances, and instrumentation errors on the measurement of rotor currents. It contributes to diagnosing the motor loading and to monitoring the insulation condition of the rotor windings even under lower fault levels. Experimental results presented for a 7.5 hp, 415 V, four-pole WRIM validate the competency of the proposed technique. [ABSTRACT FROM AUTHOR]