×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Split Phase Generators

Split Phase Generators

Split Phase Generators

(OP)
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

RE: Split Phase Generators

Quote:

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.
That doubles the voltage to ground in parts of the machine. In a higher voltage machine that'd definitely be a concern. For 120/240, I don't think it makes much difference (I don't think designer would insulate it any different knowing it would be connected this way). Just thinking out loud.

=====================================
(2B)+(2B)' ?

RE: Split Phase Generators

(OP)
Yes I was aware the L1 would see 240 instead of 120V, however as you say for LV application may not matter as the insulation is likely to be sufficiently rated. The use of the 1 to 1 transforner would eliminate this issue.I could run with it and if problems arise then have the generator rewind for full 240.

RE: Split Phase Generators

In NEMA world the center tap Jeez don't confuse a simple single phase situation by calling it a split phase or a 180 degree phase shift.
Both windings are IN PHASE.
In NEMA world the a 120/240 Volt transformer has the center tap brought out as the neutral. Voltages are L1,120V - Neutral - 120V L2.
In IEC I understand that single phase is considered to be derived from three phase systems. With this in mind, one end of the single phase winding is the neutral of the three phase system and voltages are L1, 240V - Neutral.
When I did a lot of installations of F. G. Wilson gensets, (They claimed to be number three in the world of gensets at that time.), The same generator ends were used for both NEMA systems and for IEC systems.
The voltage rating has nothing to do with the insulation strength.
The voltage rating has to do with both standard voltages and with saturation. A given winding may be rated for anywhere from 110 Volts to about 140 Volts depending on the intended application and on the intended frequency.
All of the windings are regularly checked with a 1000 Volt megger.
If the generator is intended for IEC land it will probably show the 240 Volt connection on the nameplate.
It sounds as if you intend to use a generator configured for NEMA land on an IEC system.
If you are dropping from 60 Hz to 50 Hz, don't forget to change the UFRO jumper to the 50 Hz connection. Your voltages will be unstable if you run 50 Hz on the 60 Hz UFRO connection.
Standard no-load frequency on a nominal 50 Hz set is 51.5 Hz. (+3% or 3% droop) Here also, an improper no load frequency will interfere with the functioning of the UFRO and may lead to voltage instability.

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

RE: Split Phase Generators

(OP)
The two windings are physically separate. When the voltage selector switch is placed in the 120V position the windings are in parallel (and in phase) and when in the 120/240V position the windings are in series with two separate 120V outlets and one 240V outlet. When in the 120/240 position the two separate 120V outlets are not in phase. See Attachment

If the two separate 120V sockets were in phase I would be able to join the two “Hot” wires from each outlet together. However if I were to do this I would put a short circuit across the two winding connected in series. Therefor the question as to whether the 120 windings are in phase or not is dependent on the voltage selection made. They are in phase when connected in parallel to produce 120V only.

I intent to use the generator in the Philippines which uses a combination of both NEMA and IEC type arrangements and multitude of arrangements in between. For my case the local distribution is a 240V single phase system derived from a single wire earth return high voltage distribution system. The the LV neutral in bonded at the transformer solidly to earth. Most locally available domestic distribution boards use two pole circuit breakers with no earth bars and neutral bars. I am wiring my house as per IEC practise and the main switchboard has both earth and neutral busbars. The neutral and earth bars are bonded together. A separate earth rod provided locally and bonded to the earth bar. Outgoing circuits are protected with IEC single pole MCB’s and the incomer is fitted with earth leakage circuit breaker. Philippines are a 60 Hz system and so is the generator.

RE: Split Phase Generators

What is the phase of an automotive battery? Connect two batteries with opposite polarities and then explain again about how the batteries are "Out of Phase".
It's called single phase for a reason.
Don't confuse reversed polarity with phase shift.

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

RE: Split Phase Generators

Reverse polarity IS a 180 degree phase shift. It is so regardless of frequency and even if the frequency is zero Hz. The latter situation may seem extreme, but it does exist. In an car battery, for instance.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Split Phase Generators

Yes Gunnar. I agree with you from a purist point of view. However, I refer to common usage. I suggest that the common usage would be to call this a series-parallel connection.
I find that calling a reversed polarity a phase shift is often misleading. Particularly when we deal with many phase shifts of less than 180 degrees that may not involve a reconnection.
I can't recall you ever calling a series parallel connection a phase shift.
I was intrigued by the thread title, "Split Phase Generator" I am familiar with split phase motors but not split phase generators.
For everyone who calls this a phase shift, there are several millions who would call it a series parallel connection.
Do you recall the old voltage regulators with the movable core and winding?
These had a movable, rotatable core and secondary winding. For full boost, the core would be positioned so that the induced voltage would be in-phase with the line voltage. As the line voltage increased, the controls would physically turn the secondary core and winding so that the induced voltage and the amount of boost was less. At the half-way point in the travel the induced voltage would be zero. If the line voltage continued to rise, the core would be turned further and the induced voltage would be of the oposite polarity and would start bucking the line voltage.
Some may call this a phase shift even though the induced voltage did not actually shift phase but was reduced to zero and then increased in the opposite polarity.
Arguments of this type are more suited to pub discussions. I agree that a polarity reversal may be drawn as a vector at 180 degrees to the original reference. However I would also argue that a shift implies going through the intermediate phase angles. O, 30, 60, 90 120, 150 and 180 degrees.
I would love to continue this discussion with you in a pub sometime. We could both give our minds a workout and leave leave the pub as good friends without ever coming to an agreement.

To the OP:
This has little to do with your concerns. "A Rose by any other name". The circuit will work regardless of what you call it.
You need not worry about the voltage. The windings will withstand 240 Volts and more to ground.
Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Split Phase Generators

fwiw I wouldn't disagree with using the terms terms in-phase / out-of-phase to compare polarity of two sinusoidal circuits to be series'd or paralleled, but I personally wouldn't use the term phase in any sense to apply to a dc circuit since time-shifted dc is still dc. Sorry for a tangent on terminology. As far as op's original question, I would defer to the other knowledeable members.

=====================================
(2B)+(2B)' ?

RE: Split Phase Generators

(OP)
If your reference is one of the hot wires both windings of a 120/240 supply are in phase. If the reference is the centre tap they must be 180 deg out of phase. If they were in phase, hence synchronised, there would be no voltage difference the hot wires. To reinforce the concept that reverse polarity is just the same as 180 deg phase shift relative to the center tap let’s look at a two windings of a three phase supply. The center tap is the neutral. If we assume each phase is 240V the line to line voltage is 415V. I don’t think anyone should have any difficultly see the two winding are displaced 120 deg. If we now increase displacement to 180 deg the voltage line to line will be 480V. This is exactly what is happening with a 120/240V center tap winding. The two hot wires are the line to line voltage and the two hot wire to neutral legs are the phase voltage each displaced by 180 deg.

RE: Split Phase Generators

Yes, Bill!

We need to see us in a pub and have a mental work-out! Would love that, too!

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Split Phase Generators

FAQ238-777: Questions of phase

The lingo aside, referencing the linked diagram, I take it you wish to move the ground point from the center down to the lower left hand corner. I see no problem in doing so as long as all grounding points are accessible.

RE: Split Phase Generators

This is exactly what is happening with a 120/240V center tap winding. The two hot wires are the line to line voltage and the two hot wire to neutral legs are the phase voltage each displaced by 180 deg.
LeithJS
Are you saying this is a 2 phase system?
No it's single phase

I think the term Phase is loosely applied to mean wire, winding or angle.

RE: Split Phase Generators

(OP)
If it is in relation to a cunsumer taking supply at 120V it is allways single phase. If it is a consumer taking supply at 240V with center tap being used as neutral it is then a 2 phase system (2 x 120V single phases each displaced at 180 deg relative to neutral, otherwise it would not be possible to get 240V difference between the two hot wires) They are not in phase. If they were in phase they would be synchronised and there would be no potential difference between the two hot wires. If it is a cunsumer taking supply at 240 with center tap isolated and one winding end acting as the neutral it must be single phase.

If the

RE: Split Phase Generators

Sure, an argument can be made to call this two phase. But is it helpful in any way? I believe it is only confusing. Would you call four single phase transformers connected in series four-phase power? I think calling calling a single phase transformer with a center tap 2-phase is just silly.











RE: Split Phase Generators

Calling a single phase, center tapped transformer two phase is not only silly but causes confusion with true two phase systems.
Are there any two phase systems left in North America?
I understand that there was still a 25 Cycle generating station in operation a couple of years ago, but 25 Cycle is relatively new compared to two phase. I use the term Cycles intentionally. As far as I know, the last 25 Cycle station was built years before Hertz became the recognized term for frequency.

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

RE: Split Phase Generators

180 degree phase displacements don't count.

Single phase involves no phase displacements.

Two phase involves a 90 degree phase displacement.

Three phase involves two different 120 degree displacements.

RE: Split Phase Generators

I found the title of this thread misleading;
"Split Phase Generators"
I am familiar with split phase motors. A phase displacement is produced by pairing two windings with widely different X:R ratios.
One winding is a normal motor winding with low resistance and a fair amount of inductive reactance.
The second winding has relatively high resistance and a lower X:R ratio.
No series parallel involved. Putting these windings in series would defeat the purpose and there would be no phase displacement to develop starting torque.
I thought that this thread would be about some offbeat excitation system.

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

RE: Split Phase Generators

Most of our terms are precise. The terms mean the same to all of us.
This is a dual voltage, single phase generator with two identical windings suitable for either series are parallel connection.
The controversy ensuing from calling this a split phase generator and calling a reversed polarity a 180 degree phase shift should be indication enough that these terms should not be used in this context.

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

RE: Split Phase Generators

(OP)
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.

RE: Split Phase Generators

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

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

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Split Phase Generators

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.

RE: Split Phase Generators

(OP)
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.

RE: Split Phase Generators

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.

RE: Split Phase Generators

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?

RE: Split Phase Generators

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

RE: Split Phase Generators

(OP)
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.

RE: Split Phase Generators

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources