الفهرس 
Issue of Islanding and its riskOnly 14 pages are availabe for public view
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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.