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POWER SUPPLY FOR ELECTRIC TRACTION DRIVES
ABSTRACT
Electric Traction
There is a wide variety of electric traction systems around the world, which have been built according to the type of railway, its location and the technology available at the time of the installation. Many installations seen today were first built up to 100 years ago, some when electric traction was barely out its diapers, so to speak, and this has had a great influence on what is seen today.
In the last 20 years there has been a gigantic acceleration in railway traction development. This has run in parallel with the development of power electronics and microprocessors. What have been the accepted norms for the industry for, sometimes, 80 years, have suddenly been thrown out and replaced by fundamental changes in design, manufacture and operation. Many of these developments are highly technical and complex, the details of which are therefore beyond the scope of these texts.
Because these changes have been so rapid, there are still plenty of examples of the original technology around and in regular use, so I have covered these in my articles. This is useful, since it helps the reader to get to grips with the modern stuff.

Submitted by
N.Sheethal (062510234)
Under the guidance of BY
(Mr.G.Ramana Reddy)

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fundamental POWER SUPPLY

abstract

Linear power supply
An AC powered linear power supply usually uses a transformer to convert the voltage from the wall outlet (mains) to a different, usually a lower voltage. If it is used to produce DC, a rectifier is used. A capacitor is used to smooth the pulsating current from the rectifier. Some small periodic deviations from smooth direct current will remain, which is known as ripple. These pulsations occur at a frequency related to the AC power frequency (for example, a multiple of 50 or 60 Hz).
The voltage produced by an unregulated power supply will vary depending on the load and on variations in the AC supply voltage. For critical electronics applications a linear regulator will be used to stabilize and adjust the voltage. This regulator will also greatly reduce the ripple and noise in the output DC current. Linear regulators often provide current limiting, protecting the power supply and attached circuit from over current.
The simplest DC power supply circuit consists of a single diode and resistor in series with the AC supply.

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