Favourite connection method for two phase mains?

[Faringdon]

Hi,
Which of the attached is your favourite connection method for 2 phase mains? (LTspice and jpeg attached)
The 6 diode rectifier gives you a much lower peak mains current, much smaller output capacitor, and much less ripple current in the capacitor.

[TimFox]

If you have all three phase wires available, the 6-diode rectifier gives you much less ripple for a given filter capacitance than the 4-diode rectifier (full-wave bridge) operating from two phases.
Not all customers for power supplies have all three phases available, so you need to check with the customer.
I once needed the customer's electricians to install a three-phase outlet, since my boss hadn't asked me and told the customer that single-phase mains sufficed for the high-power installation.

[Faringdon]

Thanks, and as you know, the above uses only two phases with a 6 diode rectifier. Which is best, right , or left?

[TimFox]

Your drawing on the left is a conventional three-phase rectifier.
That on the right is a conventional full-wave bridge.

[Faringdon]

Thanks, yes, but the 3 phase rect only has two phases going into it.....and its better than the one on the right.
Wondering why its not used for 2 phase systems?

[gnuarm]

Thanks, yes, but the 3 phase rect only has two phases going into it.....and its better than the one on the right.
Wondering why its not used for 2 phase systems?

Which phase is not going into the device in the left diagram???  I'm not following you at all on this.

[TimFox]

The three nodes "A", "B", and "C" feeding the rectifiers in the left diagram are three phases of a three-phase distribution.
(The neutral node is not needed for this rectifier.)

[gnuarm]

The three nodes "A", "B", and "C" feeding the rectifiers in the left diagram are three phases of a three-phase distribution.
(The neutral node is not needed for this rectifier.)

I believe the OP thinks that because he is only showing two voltage sources, that he is using two phase, rather than three phase. 

[TimFox]

In real life, his left drawing would be fed from a "delta" or "wye" transformer secondary from three-phase mains.
For the full-wave rectifier circuit as drawn, with a grounded load, no connection to the center of the wye is required, but of course the secondary windings are isolated from ground.
If the feed is not isolated from "ground", then the load must be galvanically isolated, such as a motor drive where the motor windings are insulated from ground.
Often, the "bus" voltage across the filter capacitor is not grounded, but coupled to a grounded load through a high-frequency transformer as part of the switching power supply.
Hint:  120^o is a clue for the existence of three-phase voltage.

[uer166]

"2 phase" should be same as single phase, you should get the same ripple and issues as a 1-phase supply input stage..

[nctnico]

Thanks, yes, but the 3 phase rect only has two phases going into it.....and its better than the one on the right.
Wondering why its not used for 2 phase systems?

Which phase is not going into the device in the left diagram???  I'm not following you at all on this.

The schematic is perfectly clear about this! Hint: in a 3 phase mains system, the phases are shifted by 120 degrees

The problem I see is that the device will see an odd variety of pulses and it will load the grid in a bad way (especially when the device draws a lot of power). IMHO you shouldn't design equipment like this. Either use single phase or 3 phase.

[gnuarm]

Thanks, yes, but the 3 phase rect only has two phases going into it.....and its better than the one on the right.
Wondering why its not used for 2 phase systems?

Which phase is not going into the device in the left diagram???  I'm not following you at all on this.

The schematic is perfectly clear about this! Hint: in a 3 phase mains system, the phases are shifted by 120 degrees

I don't think you understand what I asked.  It doesn't matter.  It was not directed to you.

[IanB]

Thanks, yes, but the 3 phase rect only has two phases going into it.....and its better than the one on the right.
Wondering why its not used for 2 phase systems?

The one on the left has three phases going into it (as said by other respondents). If you have three wires, each spaced 120 degrees apart, then you have three phases. There is no way to get these three wires from a three phase mains supply without having three phases present (unless you do something dumb like letting the three wires be N, L1 and L2).

[multipla]

My favourite connection method for 2 phase mains is as attached, it gives you even less ripple and because 8 it a multiple of 2 and 4 (as opposed to 6) you can do the layout even more symmetrical (better).
Would you agree?

[nctnico]

That is very clever! 

[gnuarm]

My favourite connection method for 2 phase mains is as attached, it gives you even less ripple and because 8 it a multiple of 2 and 4 (as opposed to 6) you can do the layout even more symmetrical (better).
Would you agree?

I can't tell what parts of this thread are serious and which are jokes. 

Where do you get the two AC phases aligned this way?  The original approach was using 3 phase power and calling it two phase.  If you really want to use two independent AC lines like this to minimize ripple, wouldn't they need to be 90° out of phase, not 180°? 

This way the four angles produce peaks of conducted current at 0°, 120°, 180° and 300°.  Clearly not optimal.  Better is 0°, 90°, 180° and 270°. 

Or am I missing a sarcastic post?

[nctnico]

Or am I missing a sarcastic post?

Definitely! 

[ConKbot]

Feed the two phase plus neutral into a 3 phase transformer (oversize to handle the dropped phase) and use phase shifted windings to get both a star and a delta output, and feed that into a 12 pulse rectifier. This reduces ripple currents even further.

[multipla]

Or am I missing a sarcastic post?

Yeah... And I extra signed up for this post! But I've been reading for quite some time already

[Faringdon]

I believe the OP thinks that because he is only showing two voltage sources, that he is using two phase, rather than three phase.

Thanks, yes thats right...if there are only two voltage sources, then it cant possibly be 3 called phase...even though there might actually be a third phase somewhere back in the system.

The attached LTspice (& jpeg)  shows a three phase delta supply into a 6 diode rectifier...at t = 100ms, one of the three phases gets totally switched out...leaving only the other 2 phases supplying current......as can be seen, the currents in the rectifier remain exactly the same  before and after t = 100ms....the load "knows nothing" of the supply system calamity that has just occurred.....and there is no way (inside the device with the rectifier)  to detect that a phase just got dropped.

This is definetely a 2 phase system after t = 100ms, since there are only two voltage sources remaining after the third gets switched out.

The problem I see is that the device will see an odd variety of pulses and it will load the grid in a bad way (especially when the device draws a lot of power). IMHO you shouldn't design equipment like this. Either use single phase or 3 phase.

Thanks yes, but 2-phase is a bona fide system....its used widely in the USA. USA streetlighting i think uses 2 phase (?)...multiple runs of streetlights share out the pairs of phases such that "overall", the overall 3 phase system is balanced.....even though each individual streetlight only gets 2 phases.....my betting is that 2-phase USA streetlights use the one on the left in the top post?

[langwadt]

Thanks, yes, but the 3 phase rect only has two phases going into it.....and its better than the one on the right.
Wondering why its not used for 2 phase systems?

The one on the left has three phases going into it (as said by other respondents). If you have three wires, each spaced 120 degrees apart, then you have three phases. There is no way to get these three wires from a three phase mains supply without having three phases present (unless you do something dumb like letting the three wires be N, L1 and L2).

https://youtu.be/quABfe4Ev3s

[nctnico]

Thanks yes, but 2-phase is a bona fide system....its used widely in the USA. USA streetlighting i think uses 2 phase (?)...multiple runs of streetlights share out the pairs of phases such that "overall", the overall 3 phase system is balanced.....even though each individual streetlight only gets 2 phases.....my betting is that 2-phase USA streetlights use the one on the left in the top post?

But ask yourself: how many wires go to each lamp post? And how is that different from a phase + neutral system?

[Faringdon]

Thanks, but suppose you have two 3 phase generators, and 3 runs of streetlights to power.......then its best to use three two phase "doublets" and supply a phase pair  to each streetlight run...rather than one 3 phase genny for one streetlight run, and the other 3 phase genny doing the other two streetlight runs....the load is better shared with the method of the top post.....the  "2 phase method"...the load on the gennys would be more shared.

[uer166]

I believe the OP thinks that because he is only showing two voltage sources, that he is using two phase, rather than three phase.

Thanks, yes thats right...if there are only two voltage sources, then it cant possibly be 3 called phase...even though there might actually be a third phase somewhere back in the system.

The attached LTspice (& jpeg)  shows a three phase delta supply into a 6 diode rectifier...at t = 100ms, one of the three phases gets totally switched out...leaving only the other 2 phases supplying current......as can be seen, the currents in the rectifier remain exactly the same  before and after t = 100ms....the load "knows nothing" of the supply system calamity that has just occurred.....and there is no way (inside the device with the rectifier)  to detect that a phase just got dropped.

This is definetely a 2 phase system after t = 100ms, since there are only two voltage sources remaining after the third gets switched out.

The problem I see is that the device will see an odd variety of pulses and it will load the grid in a bad way (especially when the device draws a lot of power). IMHO you shouldn't design equipment like this. Either use single phase or 3 phase.

Thanks yes, but 2-phase is a bona fide system....its used widely in the USA. USA streetlighting i think uses 2 phase (?)...multiple runs of streetlights share out the pairs of phases such that "overall", the overall 3 phase system is balanced.....even though each individual streetlight only gets 2 phases.....my betting is that 2-phase USA streetlights use the one on the left in the top post?

Then show me how you can reduce ripple with the 2-phase American system (whether it's split phase or 2-out-of-3). Hint: you can't because in those systems you don't have neutral access, and in split phase it wouldn't help anyway. If you're running 3 wires it's no longer a "2 phase system" by the usual definition. "2 phase plus Neutral", sure, but at that point just friggin use all 3 available phases.

[langwadt]

I believe the OP thinks that because he is only showing two voltage sources, that he is using two phase, rather than three phase.

Thanks, yes thats right...if there are only two voltage sources, then it cant possibly be 3 called phase...even though there might actually be a third phase somewhere back in the system.

The attached LTspice (& jpeg)  shows a three phase delta supply into a 6 diode rectifier...at t = 100ms, one of the three phases gets totally switched out...leaving only the other 2 phases supplying current......as can be seen, the currents in the rectifier remain exactly the same  before and after t = 100ms....the load "knows nothing" of the supply system calamity that has just occurred.....and there is no way (inside the device with the rectifier)  to detect that a phase just got dropped.

This is definetely a 2 phase system after t = 100ms, since there are only two voltage sources remaining after the third gets switched out.

The problem I see is that the device will see an odd variety of pulses and it will load the grid in a bad way (especially when the device draws a lot of power). IMHO you shouldn't design equipment like this. Either use single phase or 3 phase.

Thanks yes, but 2-phase is a bona fide system....its used widely in the USA. USA streetlighting i think uses 2 phase (?)...multiple runs of streetlights share out the pairs of phases such that "overall", the overall 3 phase system is balanced.....even though each individual streetlight only gets 2 phases.....my betting is that 2-phase USA streetlights use the one on the left in the top post?

Then show me how you can reduce ripple with the 2-phase American system (whether it's split phase or 2-out-of-3). Hint: you can't because in those systems you don't have neutral access, and in split phase it wouldn't help anyway. If you're running 3 wires it's no longer a "2 phase system" by the usual definition. "2 phase plus Neutral", sure, but at that point just friggin use all 3 available phases.

you need a minimum of 3 wires for two phases, and split phase is not two phases