Split Phase Generators

[LeithJS]

I have a question regarding the use of the diesel generator with 120/240 center tap winding. For American systems the center tap becomes the neutral and this effectively (relative to the natural) makes two phases 180 deg apart. We can get 2 x 120 V single phase outputs (Phase to Natural) and/or get 240 V output (phase to phase).

I want to use this generator on a 240 V multiple earth neutral (MEN) system, where the earth and neutral are bonded. Obviously I can’t do this directly. I have access to the terminals of the two 120 V windings, L1/ L2 and R1/R2. What I propose to do is joint L2 and R1 and isolate them. Bond R2 to earth and this becomes the neutral. L1 then becomes the 240V Phase.

Another though is to use a 1:1 transformer to establish the neutral on the secondary side and bond this to earth. On the primary side I would just connect R1 and L2 as before. L1 and R2 would be connected to the primary terminals of the transformer without one leg being bonded to earth.

This requires more equipment I wish to avoid. Does anyone have any experience connecting a split phase generator this way. Though more then welcome.

Thanks in advance

 

[LeithJS]

I understand how common usage of terms in different places around the world have been developed but are not necessarily in the true sense are correct. I used the term split phase as some locals where I am in the Phillipines use that term probably stemming from a single phase being split in two with separate access to the ends of each winding. However with respect to a 240V supply with center tap being used as a neutral, it canot be denied the two hot wires relative to the neutral are out of phase by 180 deg. Therefore the phases are different and in usage require two pole circuit Breakers to isolate supply. I don't think the phases need to be displaced angular to create a rotating magnetic field for them to be considered different phases.

 

[Skogsgurra]

http://www.gke.org/pdf/trefas.zip

I think that this little "app" can be of some use.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[iop95]

It's a simple 240V winding with a center tap (2x120V); in such installation central tap it's used to create a neutral, so between neutral and each "hot" leg is 120V; it's not a split phase or dual phase system.
While central tap is tied to neutral, may have illusion that hot legs are as 2 phases, but it's not true.
Think about if tap is not centred and it's at 25%; will be a (60V + 180V)/240V; such of asymmetry may help to see that is not a two phase system.

 

[LeithJS]

It is not an illusion, with the center tap being used as a neutral L1-N and L2-N are not in phase, therefore there L1-N and L2-N are different phases and therefore each must have a fault protection device. Though it may not be convention in NA to call this a two phase system, nevertheless it is. If they were the same it would be possible to connect L1 and L2 together on the belief they are the same phase. If the tap is at a different point, the two lines are now different in both phase and magnitude and are two different phases. Single-phase loads may be connected across the two phases L1 and L2, or a load can be connected from L1 or L2 to neutral. This applies even with a three phase system. The type of load connected to a system does not dictate if a system is a single phase or a poly phase supply. If this were so, a three phase system could be called a single phase system if all the loads connected to it are single phase.

 

[iop95]

It's a single phase winding with central tap connected to neutral; there are not two phases (two separate voltages displaced at any angle).
In any winding with central tap, if make tap as a reference point, "hot" connections are in opposite polarity being part of a unique induced voltage, not two voltages displaced at 180 degree.
Anyway, you may call it two phase system or split phase, no problem.

 

[stevenal]

By Extension:

Suppose you have an untapped, ungrounded winding. One cannot connect the two ends together without causing a short. Must be two phase?

Suppose you have a winding with two taps. One cannot connect any two of the four terminals together without causing a short circuit. If one of the four terminals is chosen at random to be grounded, we must have a three phase system?

Sorry, the arguments don't hold up.

Did you ever get your original question answered to your satisfaction?

 

[Skogsgurra]

This is a discussion that is unworthy of grown-up electrical engineers. You have to phase (sic) it - both arguments have their merits. No need to spill blood. We can very well live with either view. But some purists obviously feel personally insulted by a free discussion while some more practically inclined guys feel the same if local practice isn't adhered to. Known as the Jena/Heidelberg syndrome.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[LeithJS]

The original question more or less had been answered and will convert the 120/240V generstor so it will be comparable with a MEN system or in IEC spesk a TN-C-S system.

Thete are many systems and amazing variations in terminology to describe the same thing. All I would consider valid if the aim is to have a common understanding. I have seen this discussion many times before and there appears be two schools of thought. The idea I am trying to convey is that the reference point is very important when determining if two supplies are in phase or not. The load does not necessarily determine the supply arrangement.

 

[waross]

My point is that it may be well to avoid using a term that generates this much controversy. There may be subtle differences or implications between a phase shift and a phase reversal.
I'll buy the next round in the pub Gunnar.

Bill
--------------------
"Why not the best?"
Jimmy Carter