3-Phase Generator question

With a 35 kW generator, I doubt you could "get away" with just loading one phase.

Were I you, I would run two phases to each shelter. For most purposes each shelter would have two hot wires and a neutral. The wiring would be about what you have in a home and your could, if you wanted, have a 120/240 style panel for each shelter.

You say you have 4 shelters and 3 tents. You must do some kind of half ass load analysis to ensure reasonable balance BUT for a start consider something like:

Shelters:

And I would just run single phase C to the tents.

Within each shelter make some attempt to "balance" the load between the two phases.

I has some responsibility for power when I served in the military in VN. Everything was wired 3 phase 120/208. Complete waste of wire: a place that only powered a few lights and a radio would have 3 phase power.

But the military "likes" 3 phase power. Maybe because the large reefer boxes took 3 phase. Don't know.

Some of the military gensets I have seen have a tap on them for loading the generator to 120v. You will not be able to run all three phases into one and make it work. Sure hope your grounding the generator and using gfci's for people protection

"SQLit" wrote in news:JX2tc.22997$7y5.21528@fed1read03:

This is a commercial generator that is not in the army inventory yet. Unfortunately it does not have the tap.

It has 2 60amp 3-phase output heads. I am running each one to a power distribution box. The box lets me attach single phase pig-tail's to which ever phase I want for load balancing.

The generator is grounded with the standard 9-foot ground rod and each shelter and power distribution box is also grounded by a seperate 9-foot ground rod and also to a common ground plate on a star ground consisting of

I know it makes no sense to have a 60amp circuit breaker on the output and a 90amp breaker on the shelter input, but nobody ever claimed the military did things that made sense.

| I am in the US Army and I use a 35kw 3-phase 208v generator to power all my | equipment. My problem is, everything I use is 120v singe phase. I have to | use this one generator to power 4 mobile shelters and 3 tents. I currently | have the phases split so that each one is as equal to the others as | possible. I am not overly knowledgeable in electricity, but it seems like | there should be a different way for me to power all my equipment up. | | Is it possible to pull evenly off all three phases so that I have a singe | 120v feed that I can use? This way it would not matter how much equipment | I put on the system, it would draw evenly from all three phases. My | biggest reason for this is so that I have the flexibility to change my | setup as mission requires. As it is currently, If I don't need all of my | equipment, I have to readjust everything and play a guessing game to keep | my loads balanced on all three phases. | | Is this idea even possible or am I totally off base and stuck doing it the | way I am currently? | | Thanks for any info you can give me.

The way three phase generators are wired for single phase is by wiring the winding leads in configurations like:

• * * / \ -or- / \ / \

• *---* *---*---*

This derates the generator to 66% of capacity, so you'd only get 23kw out of it. You'd have to shut it all down and rewire and test for correct wiring to be sure you don't burn it up. If you aren't sure, don't do it. But there should be a FM giving these details.

If you have 2 or 3 120-to-120 volt isolation transformers available, you can wire SOME of the loads that way to finely balance things. I doubt such things are handy.

Otherwise you'll just have to measure actual loads in the shelters and tents over some period of time and juggle the balance to compensate when you have an off-time where you can cut some power to re-cable.

If you have 2-pole equipment (breaker panels, etc) in the shelters and/or tents, you can wire two phases to each and that can be easier to balance. And there will be 208 volts available if anything ever needs it.

"John Gilmer" wrote in news:40b47d7c$0$ snipped-for-privacy@dingus.crosslink.net:

My thought was not to pull off just one phase but to have some way to pull off all three evenly no matter how much load I require.

As for the load analysis, it is definately half assed. I spent 2 days plugging all the systems in in diffrent combinations to get as even a load as possible.

My sheters are only wired for single phase so I cant go in and change the way they draw off the phases. We will get new ones in 3-4 years that are configured in the way you suggest. I will definately keep your recomendation for when we get them though.

Thanx for the information.

If you are hell bent on 120V 2-wire, a 3-phase 12-lead generator stator can be 'optimized' by connecting the six coils in parallel delta, and not externally connecting anything to one of the three groups of four leads. [The output is

Id est, T1-T6-T7-T12 as "Aø", T2-T4-T8-T10 as "Bø" and T3-T5-T9-T11 as "Cø"-but not connected external of the stator.

Aø and Bø go to the 120V coffee pot and video games. Should be able to load the 3ø genset up to two-thirds of nameplate power, or about 23kW

--s falke

The best you can do is something like running phase A to, say, two shelters, phase B to one shelter, phase C to the other. And then connect the tents to the phase that has the least load. There should be either a meter switch or 3 meters on a 35KW generator to help you balance. If you don't trip a breaker on the generator, you will be OK.

I suspect that would be "good enuf for government work.|

Good luck

I take it you cannot ask your superior officer how to get the job done.

Is it possible to pull evenly off all three phases so that I have a singe

Is this idea even possible or am I totally off base and stuck doing it the way I am currently?

Thanks for any info you can give me.

is there a fourth wire on the generator? this would be the star connection. if the generator is connected star, or wye, connection the natural voltage for 120 volts would be from the star center to each phase. good luck, sammm

| My thought was not to pull off just one phase but to have some way to pull | off all three evenly no matter how much load I require.

A given single phase load is only going to be able to draw power at one phase angle. You can manipulate that to some degree with wiring tricks or transformers, but at the expense that your have low power factors on one or two of the phases. While a 120 volt load draws from one phase at a power factor of 1.0, a 208 volt load draws from two phases at a power factor of 0.866 (30 degrees), one leading, one lagging. But your loads are most likely 120 volt, not 208 volt.

If the circuits in each shelter or tent were three phase, the balancing can be done with each individual load within a shelter or tent. But if things are wired as single phase (two poles), then each shelter or tent is drawing from two phases (a pole to a phase). You can still do SOME tweaking of the balance WITHIN a shelter or tent by moving circuits between poles on the breaker panels. So if the C phase is light due to it not being connected to as many shelters/tents as A and B, you could go to the shelters/tents where C is connected, and move some of the 120 volt loads from the A or B phase to the C phase. That would make the shelters/tents themselves slightly out of balance, but to a degree that corrects the overall system.

| As for the load analysis, it is definately half assed. I spent 2 days | plugging all the systems in in diffrent combinations to get as even a load | as possible.

Did you manage the individual loads within a shelter/tent?

| My sheters are only wired for single phase so I cant go in and change the | way they draw off the phases. We will get new ones in 3-4 years that are | configured in the way you suggest. I will definately keep your | recomendation for when we get them though.

Yes you can. If a tent is fed with A and B, you can balance between A and B within that tent, and hence overall. Likewise of a tent is fed with B and C, you can move some loads from B to C to balance the system.

This is *assuming* you have control over individual loads with in each of the facilities (a shelter or tent). They are NOT usual single phase where the opposite poles are 180 degrees apart, giving 240 volts, as a home would have. Instead, these are 2 legs of 3 phase, at 120 degrees apart, and give you 208 volts between phases.

On Wed, 26 May 2004 18:10:04 GMT The Griffon wrote: | "SQLit" wrote in | news:JX2tc.22997$7y5.21528@fed1read03: | | |> |> Some of the military gensets I have seen have a tap on them for |> loading the |> generator to 120v. |> You will not be able to run all three phases into one and make it |> work. Sure hope your grounding the generator and using gfci's for |> people protection | | This is a commercial generator that is not in the army inventory yet. | Unfortunately it does not have the tap.

If you can identify the brand and model (be sure you have permission to do so before posting that), it might tell us more. But if that generator is producing 208Y/120 output, then it's doing what I expect as I posted in some other places in this thread. You do have some balancing options.

| It has 2 60amp 3-phase output heads. I am running each one to a power | distribution box. The box lets me attach single phase pig-tail's to which | ever phase I want for load balancing.

How many wires go to each shelter or tent (not counting the grounding wire). Is it 2 or 3? If 2 I assume it's 120 volts. If 3 it would be expected to be 120 volts between either phase and neutral, and 208 volts (not 240) between the phases. Surely you have a meter in your tool bag.

How did you make the phase symbol?

| s falke wrote: | |>"The Griffon" wrote... |> |>

|>>I am in the US Army and I use a 35kw 3-phase 208v generator to power all my |>>equipment. My problem is, everything I use is 120v singe phase. I have to |>>use this one generator to power 4 mobile shelters and 3 tents. I currently |>>have the phases split so that each one is as equal to the others as |>>possible. I am not overly knowledgeable in electricity, but it seems like |>>there should be a different way for me to power all my equipment up. |>> |>>

|>

|>If you are hell bent on 120V 2-wire, a 3-phase 12-lead generator stator can be |>'optimized' by connecting the six coils in parallel delta, and not externally |>connecting anything to one of the three groups of four leads. [The output is |>120V 3? 3-wire delta.] |>

|>Id est, T1-T6-T7-T12 as "A?", |>T2-T4-T8-T10 as "B?" and |>T3-T5-T9-T11 as "C?"-but not connected external of the stator. |>

|>A? and B? go to the 120V coffee pot and video games. Should be able to load |>the 3? genset up to two-thirds of nameplate power, or about 23kW |>

|>--s falke |>

|>

|> |>

| How did you make the phase symbol?

A phase symbol? Hmm. That must be what the "?" were supposed to be.