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

 

[electricpete]

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.

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(2B)+(2B)' ?

 

[LeithJS]

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.

 

[waross]

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

 

[LeithJS]

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.

 

[waross]

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

 

[Skogsgurra]

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

http://www.gke.org

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

 

[waross]

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

 

[electricpete]

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.


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(2B)+(2B)' ?

 

[LeithJS]

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.

 

[Skogsgurra]

Yes, Bill!

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

Gunnar Englund

http://www.gke.org

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

 

[stevenal]

faq238-777

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.

 

[roydm]

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.

 

[LeithJS]

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

 

[Compositepro]

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.

 

[waross]

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

 

[davidbeach]

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.

 

[waross]

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

 

[stevenal]

Are there any two phase systems left in North America?

According to [link]https://en.wikipedia.org/wiki/Two-phase_electric_power[/url], yes.

 

[waross]

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