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Abstract
NOTICEABLE trend in power systems nowadays is the emer! distributed harmonic-producing loads. These loads typicaJJy have COI sizes and are distributed alJ over an electric network. Traditional I assessment techniques have difficulties in detcnnining the collective ( effects of these sources. These difficulties are due to two factors. One is that th voltage distortions change the harmonic generation behavior of the distributed hi producing loads. Both the amplitude and phase angIe of the harmonic current injec load vary according to the degree of supply voltage distortion. The former effect attenuation while the latter effect is caIled diversity. Both effects tend to ree harmonic currents produced in the system, resulting in reducing hannonic distorti( in the system. The second factor is the random variations of the loads. It is neCf determine the probabilistic harmonic distortion levels in such cases.
The fundamental causes of power system harmonics can be categorized as foJJows: a) Device nonlinearity. This includes such devices as magnetic core reactors, trans and induction motors, due to the saturation behavior of their magnetic elemel electric arc furnace (EAF) is another example that has nonlinear resistance variati to the ionized gas (plasma).
b) Non-sinusoidal flux distribution in the stator of electric machines.
c) Periodic switching of power electronic equipment used in the generation, transn distribution and utilization levels of power systems.
Capacitor banks are commonly used to compensate reactive power, but the re~ between these capacitors and the system reactance can worsen harmonic disturbance Harmonic problems are solved by different methods, shunt filters being the commonly used. These filters can reduce voltage distortion in a distribution systc compensate reactive power. Passive filtering is the most economical and effective n The capacitors in passive filters provide as well reactive power compensation to ir power factor.
There are different studies on reactive compensation and filter design in the Iiteratu1 purposes of harmonic filter planning are to reduce the harmonic pollution in distribution system and to diminish the harmonic distortion, which insure th equipment can operate correctly with power factor correction.
The &equency-scan technique is usually the first step in harmonic analysis because provide some insight into system behavior at harmonic &equencies. It is use determine possible resonance frequencies that might cause equipment damage, the Of tuned filters, and the impact of their connection. Frequency scan analysis is proba~ only viable method at present to identify the existence of resonance and to determi resonance frequency.
Harmonic resonance is caused by the energy exchange between capacitive elemen1 inductive elements in a system.
This thesis presents the harmonics phenomena and their response in the electrical I system indicating the sources of harmonics and their effect on the system.
A five-bus system is selected for the harmonic analysis. The current and voltage waveforms are measured and analyzed to determine various orders of harmonic components. These orders of harmonics are used in the computer simulation to determine the harmonic voltage and current distortion factor at the buses of the system, and the scan of impedance. In addition, proper filters are designed by replace existent capacitor banks as passive filters at candidate bus to alleviate the harmonic problems. Current, voltage and scan impedance shapes are recorded before and after the filter installation to show the effect of the filter on improving the harmonics distortion problems.
A comparison between Several Harmonic Mitigation Schemes is studied. The results indicate the effect of applying different harmonic filtering combinations