3 phase rectification confussing

[windcruiser]

Question: The 3 phase rectification using two bridge rectifiers as explained in www.windstuffnow.com. My worry is after rectifying the first and second phase with the first rectifier; the third phase only uses one AC leg of the second rectifier with no return to the generator though the positive and negative are well tapped. With the second brodge rectifier without a return to the generator (say either utilizing phase 1 or 2 as return or the starpoint from the genny as return. This third phase can not flow current and seems lost.

by the way I am ok about the Delta rectifier using six single diodes

Any ideas from the three phase Gurus.

Hope this doesnt get kicked out!

Simon

[Trivo]

I read your post and others comments http://www.fieldlines.com/story/2005/5/11/65850/9815

you can connect the extra AC pin to the other reficifier AC pin but apparently it is not required but i like things ballanced

Trivo

[Trivo]

Simon i have noticed that the first post is in controlls and this one is in wind so it is there just got to find it. at the top ot the page is a link to "everything" and every posting shows up when you hit it

Trivo

[Flux]

What is a delta rectifier using 6 single diodes?

A 3 phase bridge rectifier consists of 6 diodes, 3 have anodes connected to the dc and 3 have cathodes connected to the other dc line.The 3 ac lines go to each junction of an anode and a cathode.

It makes not a scrap of difference whether you have 6 individual diodes, 6 in a 3 phase bridge or 4 in one single phase bridge and 2 in another. It also doesn't matter if the ac supply is star or delta, for star the star point is not used.

Conduction takes place at any time via a pair of diodes, one conducting to the dc positive and the other to the dc negative, they swap over every 60 deg. the circuit is always completed via the dc lines and these are connected to the bridge that is only half used and seems to be worrying you. You can if you wish connect the un used ac connection to one of the others but it is not necessary.

Also you don't get 2 phase under any condition, if you remove one ac connection it becomes single phase.

Hope this clears up the confusion, someone would have screamed a long time ago if the link on Ed's site was wrong.

Flux

[drdongle]

Didn't we cover this last week? there is no problem the extra 2 diodes are simply unused and redundent.

[DanB]

Like everyone said - what Ed's got there is fine, and the same setup works for either Star, or Delta - the rectifiers dont care.

But if you're using 2 bridge rectifiers allready, why not add one more?  One full wave bridge per lead with it's AC leads tied together looks/feels a bit simpler and handles twice the power.

[ghurd]

I think you may get a feel for it if you draw out the diodes that are in the bridges.  

A bridge is just 4 diodes.

Draw the 2 that are being used in the 'partly connected' bridge,

and all the other 8.

G-

[windcruiser]

Thanks guys,

That was quite enlightening.

simon