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Dr. Waleed Abdel Aziz Salem Attia :: Publications:

Title:
IMPROVING POWER TRANSFORMER CHARACTERISTICS BY USING K- FACTOR AND NARROW BAND WIDTH TRANSFORMER (NBT) SYSTEM (PhD Thesis )
Authors: O.E. Gouda, G.M. Amer, W.A.A. Salem
Year: 2012
Keywords: Not Available
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Local/International: Local
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Abstract:

Power transformers represent the largest portion of capital investment in transmission and distribution substations. One of the most important parameters governing a transformer’s life expectancy is the hot spot temperature value. Temperature rise in a transformer depends on variety of parameters such as ambient temperature, output current and type of the core. In this thesis the IEEE model for hot spot and top oil temperature calculations is introduced also the modified IEEE model for transformer temperature calculations at varying ambient temperature and load cycle is investigated. For more accurate temperature calculations, a new thermal model based on simple electrical equivalent circuit by MATLAB is suggested. This method avoids the complication associated to accurate estimation and is in very good agreement with practice. The significance of harmonics in power systems has increased substantially due to the use of solid state controlled loads and other high frequency producing devices. An important consideration when evaluating the impact of harmonics is their effect on power system components and loads. Supplying non linear loads by transformer leads to higher losses, early fatigue of insulation, and reduction of the useful life of transformer. To prevent these problems rated capacity of transformer supplying non linear loads must be increased. This thesis reviews the non linear loads effects on the transformers and the standard IEEE procedures for derating of the transformers which are under distorted currents. The hot spot, top oil and losses of a typical 25 MVA 66/11 kV ONAF cooling transformer will be evaluated using analysis and simulations in MATLAB/Simulink based on useful model of transformer under harmonic condition and results are compared. K-factor transformers are specially designed to accommodate current harmonics. K-factor transformers are preferred because they have additional thermal capacity of known limits designed features that minimize harmonic current loss. In this thesis TOSHKA pumping station as case study is simulated to investigate and calculate K-factor with and without using harmonics filter. The results obtained by simulation are compared with measured values from the station. Narrow bandwidth transformer (NBT) reduces line distortion within isolation or power transformers. NBT transformers restrict electromagnetic energy to a very narrow passing frequency band. This patented technology gives the transformer the ability to dampen distortion on the line due to harmonics and spikes. Our goal of this thesis is to design the NBT transformer and study its effect in harmonics reduction.

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