Date of Award

12-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Electrical Engineering

Advisor

Girgis, Adly

Committee Member

Makram , Elham

Committee Member

Gowdy , John

Abstract

Under frequency load shedding schemes have been widely used, to restore power system stability post major disturbances. However, the analysis of recent blackouts suggests that voltage collapse and voltage-related problems are also important concerns in maintaining system stability. For this reason, both frequency and voltage need to be taken into account in load shedding schemes. The research undertaken here considers both parameters in designing a load shedding scheme to determine the amount of load to be shed and its appropriate location. An introduction about the need for a load shedding scheme and the purpose of doing research on this particular topic is given. This is followed by a discussion on the literature review of some of these schemes. The discussion is divided into two parts. The first part is about the actual load shedding schemes used in the power industry world wide. The second part gives a detailed overview about the two types of load shedding schemes, namely the under frequency and under voltage load shedding schemes.
The methodology used for the proposed load shedding algorithm includes frequency and voltage as the inputs. The disturbance magnitude is estimated using the rate of change of frequency and the location and the amount of load to be shed from each bus is decided using the voltage sensitivities. The methodology describes the algorithm in a stepwise manner and gives brief information about the test system and the PSS/E software used to model the disturbance. The test systems used are the IEEE 39 bus system and IEEE 50 bus system. The disturbances modelled are the loss of a generator for various buses and the loss of transmission lines for various cases. The observations and results obtained from the simulations comprise of the frequency and voltage plots before and after applying the proposed load shedding scheme. The load shedding scheme is implemented on an equivalent system provided by Duke Energy. The data has been collected from a Duke simulator. The calculations for determining the magnitude of the disturbance and the amount of load shed from each bus are also presented here. The conclusion chapter includes the summary of the observations and suggestions for future work.

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