Evaluation of Passive Islanding Detection Methods for Line to Ground Unsymmetrical Fault in Three Phase Microgrid Systems: Microgrid Islanding Detection Method

Distributed Generators (DGs) are incorporated in the power distribution systems to develop green energies in microgrids. Islanding is a challenging task in a microgrid. Different types of islanding methods, e.g. local and remote methods, have been developed for handling this task, with local methods being easier to implement, while remote methods are communication-based and costly. The local methods are classified as passive, active, and hybrid, out of which the passive methods are more simple and economical. In this paper, a passive islanding detection method is proposed to detect single line to ground fault. This fault is considered to represent the 60 to 70% of the total un-intentional faults of this category. The available passive methods cannot detect islanding at lower power mismatches as the variations in voltage and frequency fall within thresholding values. In this method, the voltage signals are first retrieved at the targeted DG output and then the phase angle is estimated. Finally, the phase angle is differentiated to get Rate Of Change Of Voltage Phase Angle (ROCOVPA) to detect islanding, and then it is compared with the Rate Of Change Of Frequency (ROCOF) at zero percent power mismatch. Simulation results depict that the ROCOVPA is more effective than ROCOF. The proposed method not only reduces detection time and Non-Detection Zone (NDZ) but is also stable during non-islanding cases like load connection and disconnection to avoid nuisance tripping.

Preventing third zone maloperation during power system stressed conditions

The back-up third zone unit of distance relay may issue nuisance tripping command during different system critical events like power swing, voltage stress/instability and load encroachment. Since, such events are system symmetry phenomenon, the protection unit will not always able to discern them from three phase (symmetrical) fault in the distance relay third-zone region. The conventional relay algorithm fails to make a proper decision and results in unwanted tripping. This may further lead to system blackout. To mitigate this problem, a new approach based on the average rate of change of current (ARCC) is proposed. The method will work in integration with the conventional distance relay impedance setting algorithm to provide better results. The main advantage of the method is that it considers only local end current information. Within one power cycle, an accurate decision can be taken by the protective relay. The proposed method is validated considering IEEE 39-bus New England test system and the Indian regional power grid model modeled using EMTDC/PSCAD software. The simulation results for various critical cases and comparative analysis with existing methods shows effectiveness of the proposed method.

Impacts of Distributed Generations on Power System

With increasing population and urbanization, the demand of electricity also increases day by day; to fulfill this demand, clean and environment-friendly distributed generations are being installed, but these have some issues in power section. With the integration of DG load curve is levelized, feeder voltage is improved; loading effect on the transformer and branches is reduced, and provides electricity with no pollution. This chapter investigates impacts of DGs to the power system; distributed generation means to generate electric power near the power consumption point. Power quality and reliability can be enhanced by the interconnection of distribution generation to an existing distribution system. However, there are so many effects of distributed generation e.g. changing of load losses, increasing of short circuit levels, voltage transient, congestions in the system branches, power quality, and reliability and network protection issues such as false tripping, nuisance tripping, unintentional islanding, neutral shifting is mainly affected.