Chapt 1-0 Reading_Applications-PE

Chapt 1-0 Reading_Applications-PE - Electronic ballasts: ,...

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Electronic ballasts: , also called solid-state ballasts, are those power electronic converters used to supply discharge lamps. The modern electronic ballasts with the development of low cost power MOSFETs allow to supply fluorescent lamps at frequencies of several kilohertz and increasing lamp luminous ef±cacy ['efik si] ə by operating at these high frequencies. The main bene±ts of electronic ballasts are the increase in the lamp and ballast overall ef±ciency, increase in lamp life, reduction of ballast size and weight, and improve-ment in lighting quality. UPS: Power distortions such as power interruptions, voltage sags and swells, voltage spikes, and voltage harmonics can cause severe impacts on sensitive loads in the electrical systems. Uninterruptible power supply (UPS) systems are used to provide uninterrupted, reliable, and high quality power for these sensitive loads. Applications of UPS systems include medical facilities, life supporting systems, data storage and computer systems, emergency equipment, telecommunications, industrial processing, and on-line management systems . The UPS systems are especially required in places where power outages and fluctuations occur frequently. A UPS provides a backup power circuitry to supply vital systems when a power outage occurs. In situations where short time power fluctuations or disturbed voltage occur, a UPS provides constant power to keep the important loads running. During extended power failures, a UPS provides backup power to keep the systems running long enough so that they can be gracefully powered down. Most of the UPS systems also suppress line transients and harmonic disturbances. Generally, an ideal UPS should be able to simultaneously deliver uninterrupted power and provide the necessary power conditioning for the particular power application. Therefore, an ideal UPS should have the following features: regulated sinusoidal output voltage with low total harmonic distortion (THD) independent from the changes in the input voltage or in the load, on-line operation that mean zero transition time from normal to back-up mode and vice versa, low THD sinusoidal input current and unity power factor, high reliability, high ef±ciency, low EMI and acoustic noise, electric isolation, low maintenance, low cost, weight, and size. Obviously, there is not a single con±guration that can provide all of these features. Different con±gurations of UPS systems emphasize on some of the features mentioned above. Classi±cations of UPS systems are described in Section 24.2 Off-line UPS: Standby-UPS This con±guration of UPS system is also known as “off-line UPS” or “line-preferred UPS” . It consists of an AC/DC converter, a battery bank, a DC/AC inverter, and a static switch . A passive low pass ±lter may also be used at the output of the UPS or inverter to remove the switching frequency from the output voltage. The static switch is on during 1
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the normal mode of operation. Therefore, load is supplied from the AC line directly
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This note was uploaded on 11/02/2009 for the course ECE ece464 taught by Professor Abc during the Spring '09 term at Jacksonville College.

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Chapt 1-0 Reading_Applications-PE - Electronic ballasts: ,...

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