EE 587_HW Part 1


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HARMONICS IN POWER SYSTEMS Red Book Revision Assignment By Daniel Olusola Krishna Chaitanya Nutukurthi 9.1 Introduction Harmonic currents are a phenomenon that has existed since the beginning of the utilization of alternating current. It is only recently, however, that dealing with harmonics has become a problem to other than a small segment of the electrical industry. The reason is that the majority of loads in electric power systems were linear; that is, the waves shape of the current mirrors the wave shape of the applied voltage (ohms law characteristic). For example, incandescent lamps and, generally, induction motor loads, required sinusoidal currents when sinusoidal voltages were applied to them. However, conditions have changed with the introduction of new technology using semiconductor devices. With these versatile devices, we are better able to control the currents to the load in ways that increase the efficiency and/or controllability of the load. The new technologies almost always improve operating and control capabilities, but they also may be introduced for cost savings, such as replacing the more expensive ‘linear’ power supplies with switching-mode devices. They may actually be more expensive than alternate methods of control, but they are much more flexible, as in the case of motor controllers. Use of these devices, however, has resulted in nonlinear loads that require non sinusoidal currents containing harmonics from the power system. 9.2 Importance of understanding effects of harmonics As a result of the thrust for more efficient use and control of electrical energy, several new harmonic sources have been created, of which the static power converter is the most important. This device is used in a variety of adjustable-speed drives, switched-mode power supplies, frequency changers for induction heating, and other applications. In addition to these new and additional applications, semiconductor devices are used in static switches that modulate the voltage applied to loads. Examples of these are soft starters for motors, static var compensators (SVC), light dimmers, electronic ballasts for arc-discharge lamps, etc. The most popular generator of harmonic currents and voltages appear to be three phase SCR six pulse converters and three phase six pulse diode bridges, generally used with DC and AC drives. A more recent development in ower electronics for AC to DC conversion is the Voltage Source Converter (VSC). This is a transistor coverter that can be controlled to produce low distortion line currents and u nity input power factors. It has been estimated that by the year 2010, 50% of the power produced will be modified by semiconductors, especially silicon-based technologies, to alter its sinusoidal characteristic in order to improve the efficiency of its use. However, when the power is modified by these semiconductors, the resulting current requirements on the power system are non sinusoidal. In addition to these new non
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This note was uploaded on 02/04/2011 for the course EE 587 taught by Professor Dr.mohammedsafiuddin during the Spring '11 term at SUNY Buffalo.

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