Need help with 3-phase balancing system

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#1
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Hello guys, need your help.
I have two three-phase generators "“ one with power about 20 kW, and other with bigger power (about 50 kW). But I always must use the bigger one because of phase (current) unbalancing near 40-50% (which I could not correct for some reasons). From my calculating, for all loads smaller generator is quite enough. So, what I need is a device for balancing three-phase system to reduce cost of fuel, etc.

Are there some complete systems from any manufacturers that will do the job? Anyway, all references and suggestions should be helpful, because google gives only patents references.
Thanks.

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http://www.basler.com/html/rscde...

I googled for digital control for generator

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I do not need advance control for generator. What I need - is a device (special regulated transformer, in fact) that will redistribute power from phase to phase, keeping total generator load (smaller generator) about 95%. I need it when each phase has not the same load. For example, here some abstract from one article

Quote:
"A load balancing transformer (LBT) has already been suggested for improving the unbalance of three-phase primary currents. Each phase includes one extra pair of coupling windings in addition to the usual primary and secondary windings. Two coupling windings, located on two different phases, are made in series, where the resulting circuit is then reversely paralleled with the secondary winding placed on the third phase. Under unbalanced conditions, the load currents are distributed between the coupling and secondary windings that are supplied through different primary phases..."

I want something like this transformer. I could not find one (20-30kW). Another approach - to use powerful 3-phase UPS, that has DC sectione (inverter like this). But it's too expensive and unreliable, I sink.

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Your problem description is somewhat unclear.

One way of reading it it that you have two three phase generators, phase locked, and you need a device to preferentially load the larger generator, invoking the smaller generator only when current demand exceeds what the large one can provide.

The other way of reading it is that you have a large generator with unbalanced currents, and you want to use the smaller one to provide balance.

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The third way to read it, and the way I read it, was that he has two generators and one unbalanced load which he cannot balance.

The larger generator is happy with the unbalanced load.

However, the total power requirement of the load is within the capability of the smaller generator and for reasons of efficiency and cost he would like a way of using the smaller generator instead.

So he needs a device to interpose between the load and the generator to correct the imbalance.

I suggest he searches for "static balancer" transformer.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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Having dug out my trusty copy of J&P and refreshed my memory...

1) Even a static balancer will leave the 3-phase side with some imbalance. How much depends very much on the load you have connected.

2) You might achieve better results with 3 3-phase to 1-phase transformers. Again, you will end up with each one giving you an imbalance on the 3-phase side but you ought to be able to arrange the wiring to cancel most of these out.

Without a lot more information about the loads it's not possible to do more.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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Are the loads constant or do they vary with time? Especially the extra load on the phase that is unbalanced.

Are the loads 3-phase loads or are there many independent single-phase loads on each phase?

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Brian Fairchild wrote:
The larger generator is happy with the unbalanced load. ... the total power requirement of the load is within the capability of the smaller generator and for reasons of efficiency and cost he would like a way of using the smaller generator instead. So he needs a device to interpose between the load and the generator to correct the imbalance.
I suggest he searches for "static balancer" transformer.

That is correct.
Thanks. It is my lack of terminology knowledge. But anyway, I will offer the easiest way (as I think so far) - 3 3-phase to 1-phase.

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I think you really need to get an expert in. 3-phase to 1-phase transformers are not exactly off the shelf items and need to be designed in for the system. And they are far from cheap.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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It is true, and question of cost is not the last one. You see, due to small research I've mayd in last couple days in field of electroenergetics, including this forum comments (thanks), I have at least 3 realistic solutions of this problem. Implementation any of them will be not cost recovery at all. Payback are way too far. And cheaper to redisighn power-supply system itself with redistribution 3-phase and 1-phase power consumers. However, with greater power (>100kW) all balancers would have positive economical effect. To get an expert in is (in fact) my main goal, but to do this I must have the strong base for further explanations.
I think, you'll understand me.
Thanks to all again.

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Hello,

You need to do a load analysis. Go to each branch circuit panel and check the amperage of each circuit and the corresponding neutral conductor and check the Hz with a FLUKE 97 or similar. In each case you can calculate the power factor and determine what is causing such a huge imbalance, be it an inductive or capacitive load. You can then implement some power factor correction or move a portion of the problem loads to another phase. If there is this much imbalance adding a K rated transformer will not help as much as redistributing the load. I did an in-depth evaluation for a MACY's store here in St Louis that had tons of electronic ballasts and was WAY out of balance. The trick becomes finding which three phase circuits are combined on a neutral. You can destroy equipment on a multi-wire branch circuit if you do not understand 3 phase systems. Often times when you go to move some of the imbalance you must add a neutral conductor and break the problem circuits out of the multi-wire branch. There is labor involved, but it is the only option. You can quickly find imbalance by taking amperage readings on the neutral conductors. Or it may not be from harmonics at all - it could just be all your equipment is on the same phase.

Again - if your system is this out of balance then something else is going on. You should understand enough about your loads to know why one phase has so much load. Also, ensure that you have provided adequate grounding and bonding on your service AND especially on the generator. Also, make sure the jumpers on the taps of your generator are correct - if they are wrong this could be causing the issue!

Is your system a 3-phase Y or a Delta? What are the phase-to-phase and phase-to-ground voltages? What type of grounding / bonding are you using? What type of generator?

John

Just some guy