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12 pulse rectifier output and filter circuit

Discussion in 'Power Electronics' started by Dinesh Dangi, May 10, 2018.

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  1. Dinesh Dangi

    Dinesh Dangi

    May 10, 2018
    Parameters:- 3 phase 115/200 volts AC Input, Input Current at full load is 18 Amps per phase at the 200-amp output, Input Frequency is 380 to 420 Hz, DC output is 28 volts (Nominal) Current is 200 amps, Output ripple is 1.5-volt maximum Question : on transformer secondary side it is star and delta connection with rectifiers (check the link: 12 pulse rectifier). In this transformer, secondary first is 12.5 volt and second secondary voltage is 21.6 volt approx. which is line to line is 21.6 and phase to phase is 12.5 in star connection.for all transformers it is like this. Now my question is I want to know the output voltage of the rectifier circuit. can someone explain me the working of 12 pulse and also how to calculate output voltage. 2nd question: the filter circuit which you can see in the image is what type of circuit? you can see the value of capacitors like c5 is 4uf, c4 800uf, c6 40uf, c7 0.22uf AND c1, c2, c3 is 2uf, L is 8uH, and resistance is 60 ohm. how this capacitor value calculated? and also what is the use of c1,c2,c3? Thank you in advance. please explain if you know anything about the circuit. Note: B1 is the Fan for cooling.

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The 3 phase rectifier is described e.g. here.
    The filter is an LC filter. Your favorite search engine will show up lots of hits for LC filters. Study the description that you are most comfortable with.
    The workings of a smooting capacitor are also described in many ways. One is e.g. here. The exact value is often not calculated but a ballpark figure of 1000 µF per 1 A of current is used. Different types and values of capacitors are sometimes combined to improve high frequency performance of the filter.
    Dinesh Dangi likes this.
  3. duke37


    Jan 9, 2011
    You have three bridge rectifiers with the outputs summed. The peak output voltage voltage will be the voltage between (1) and (10) times root 2.

    The filter is to smooth the output voltage and the component values will depend on the ripple which can be permitted. R1 is posibly to limit the voltage difference between the loaded and unloaded state. Note that a three phase rectifier, the voltage out never drops to zero as it does with single phase so the job of the filter is easier.

    C1, C2 and C3 are connected across the mains and are there to reduce harmonics being fed back into the mains. I once worked with a DC motor which fed such a lot of harmonic energy back into the mains that the capacitors in the fluorescent lights passed enough current to blow the fuses. I was not popular.
    Dinesh Dangi likes this.
  4. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    The OP isn't providing us with the whole picture. The link that was provided was to a single image from a paper that purported to describe various harmonic mitigation (suppression) techniques for three-phase power supply systems.

    Fortunately, unlike many published papers, this one isn't hidden behind a paywall. Interested folks here at EP can read the entire paper at this link.
    Dinesh Dangi and Harald Kapp like this.
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