Hi friends,
I am looking for rough idea how to convert 3 phase ac to dc . please help

 

Hi
You can design a 6 or a 12 pulse converter to do that.
You can try these links............................http://en.wikipedia.org/wiki/HVDC_converter
or even this one..........................................http://circuitsplanet.blogspot.in/2014/11/firing-circuit-for-12-pulse-hvdc.html

 

first thought i have is standard rectification with diodes. is there some reason you cannot do it thst way?

 

Use six diodes in a bridge formation,do you intend on regulating it also,what voltage?


http://hackedgadgets.com/2010/10/05/3-phase-rectifier-basics/

 

Actually I want to convert 3 phase AC (which is about 415V here) and give the output to a dc motor. Is it better to use diodes or thyristors in this case ?

 

Thank you Shabbir_Ahmed , Dodgydave and Kermit2 for your response

 

If you want to vary the speed , then use thyristors,you can buy a dedicated ready made one cheaper.

 

Thanks. Is there any simple (cheap) way to reduce or remove the ripples in the output. Is a filter practical in this case??

 

Is there a reason why you're not using an AC motor?

 

Actually I am using the dc motor to test the response for RLE load. I wanted a way to remove ripples so that I won't screw up the dc motor.

 

the ripple will bother you more than the motor. they are tough and work with disgustingly noisy, poorly shaped and unfiltered power. application should tell us more about what kind of filtering yout motor truly needs

 

Thanks. Is there any simple (cheap) way to reduce or remove the ripples in the output. Is a filter practical in this case??

The motor itself makes a pretty good filter. That's one of the reasons that PWM waveforms can be used so successfully with DC motors.

 

Thanks. Is there any simple (cheap) way to reduce or remove the ripples in the output. Is a filter practical in this case??

3 phase SCR full-wave bridges have been used for decades for DC servo control, you do not need ripple removal with 3ph due to the low percentage ripple level compared to 1ph.
Max.

 

The unfiltered output voltage ripple from a 3-phase full-wave bridge is <5% so should not affect the operation of a DC motor, as Max noted.

 

Actually I want to convert 3 phase AC (which is about 415V here) and give the output to a dc motor. Is it better to use diodes or thyristors in this case ?

I think it would be good to use an electrician because that amount of power is incredibly dangerous. You have to go, "Full Safety Practices" because you might not survive even one mistake.

 

I think it would be good to use an electrician because that amount of power is incredibly dangerous. You have to go, "Full Safety Practices" because you might not survive even one mistake.

I fully concur -- if you are asking the kinds of questions you are asking, then there is a REAL good probability that you really don't have the level of knowledge and experience to safely work with these kinds of systems unsupervised. So pay the money to get someone that can supervise and educate you about these systems -- the cost is minimal compared to the cost of getting tangled up with this kind of power, even if the only result is damaging some equipment.

 

Actually I want to convert 3 phase AC (which is about 415V here) and give the output to a dc motor. Is it better to use diodes or thyristors in this case ?

For only rectification; 6 diodes will do fine, you can replace 3 of the diodes with thyristors if you want to control the output.

 

I think it would be good to use an electrician because that amount of power is incredibly dangerous. You have to go, "Full Safety Practices" because you might not survive even one mistake.

This is slightly higher voltage but the same effect can be imagined with 415 vs. the 480 3-phase here. I have a screw driver in my maintenance dept that was dropped across some similar power sources - not much left. A small slip of a screw driver, or a poorly tightened lug can cause some major damage in a fraction of a second. By damage, I don't mean the building.

 

In my first experience with 440V 3 phase, one leg of the disconnect didn't disconnect. I'm lucky I only lost my screwdriver!

 

found the remnants of a squirrel(fuzzy tailed rat) under a transformer pole. 14.4 kV! it looked sorta of squirrel like still, but up close it was just a piece of black charcoal. a very un-natural end for the rat with a pretty tail.