الفهرس | Only 14 pages are availabe for public view |
Abstract The traditional view of the power system is characterized by a unidirectional power flow from generation stations to consumers. Power system deregulation gave impetus to a recent view by introducing distributed generators (DGs) into distribution systems, leading to a bi-directional power flow. Several benefits of embedding DGs into distribution systems, such as increased reliability and reduced system losses, can be achieved. The growing number of DGs in the electrical system increases the risk of unintentional islanding. Power system islanding in the event that a part of the grid is continuously powered by the DG, while it is already electrically separated from the power grid. Since the island is unregulated, its behavior is unpredictable and voltage, frequency, and other power system parameters may have unacceptable levels, which may cause a hazardous effect on devices and the public. According to the IEEE Standard 1547, DG shall detect any possible islanding conditions and cease to energize the area within 2 sec. In this dissertation, islanded and normal operations have been distinguished in low voltage distributed generator networks by connecting different types of loads and applying a lot of expected utility faults to the distribution system. There are many different kinds of anti-islanding or loss-ofmains protections. Some are implemented in practice while others are still on a research-level. This thesis provides an analysis of the benefits and drawbacks of methods that are applied today. The main contribution of this thesis is to propose two novel islanding detection methods and investigate their performance. Method 1: utilizing hybrid passive methods using the rate of change of power with terminal voltage and Method 2: utilizing hybrid passive-active methods with a fuzzy logic classifier. The proposed methods have been simulated for various operating conditions, and the results verify that the proposed methods correctly detect the islanding operation, and avoid faults tripping. Finally, a comparison between the two methods with the traditional passive islanding methods and updated methods in literature has been done to differ between islanding and non-islanding events in terms of the time of detection, nondetection zone, and accuracy. A dynamic model was built in MATLAB/Simulink for the distribution network, where the two methods were simulated and applied to the DGs. |