Thanks

This may help

I believe this 32 KW is not single load. It will be total load of various single phase equipments. connect 10KW in phase 1, 10KW in phase 2 and 12 KW in phase 3.(

Yes! Such type of connection is called STAR connected load. Check the working current of equipments and divide with 3 and then connect.

It is a single load, single phase supplied,

what is that equipment ?, Boss

What difference would be? it is a galvanizing line

Thanks anyway,

I found a fair solution by the hint of dvmdsc

the idea is to keep the current balanced on our genset,

it has a single phase SCR bridge with voltage control , than a single phase transformer, than a diode rectifier........

If I have to change to 3 phases I will have to change the SCR bridge, the transformer and the output stage diode bridgae..... I will use a SCOTT arrangement of transformar, this will give a better current distribution over the 3 phases

Thanks and regards to all the posters

I will be interested to understand finally what you implement. What I told you about full bridge diode rectifier bridge- is cheap and effective. Ordinary 3 phase step down transformer gives necessary low voltage further process. Using SCR bridge, you will be implementing phase angle control- giving rise to lot of harmonics (especially when your load is 32 KW). I am surprised the utility has not penalized you. Moreover SCR bridge requires gate current driver etc etc. But anyway let me know how you have proceeded. I was heading testing and customer support of a division which made power SCRs and diodes

As far as I understand, the power is generated with his own generator. Does a Utility penalize in this case? Don't get me wrong: the process might be simplified, but I also think they have build up a lot of experience with their existing process parameters.

yes , this plant use their own generator, and the equipment is already here and running

the issue is to balance the load on the 3 phases of the generators,

changing all the bridges from single to 3 phases will stop the production for one week, which is more expensive than any other "quick " solution as addind SCOTT transformers, which will take only few hours to implement Thanks all for the help

SCR Bridge (phase control)is being used for long time with great reliability.

Is that mean it dead now?

Sorry to comment that the above proposal does not really solve the problem. The current values may be equal; but their phase difference will be different. One phase will have leading power factor and the other one a lagging power factor. Net result will be that the currents in the three phases, though equal in value are vectorially not equal and result in a heavy neutral current.

Please check the possibility of putting this single phase load on one phase and try to distribute other loads on the other phases to make as good a balance as possible.

Scott Transformer (3-Ph to 2-Ph) Open Delta Transformer etc., are all solutions which provide equal current, but not really (vectorially) equal. The better attack the problem taking all loads to be fed by the generator instead of looking at a single single phase load.

that is imposible, because, you have a 2 phases consumer, and the supply is 3 phases, the only way of balance if you have another equipments, to connect and balancing the loads in power supply.

I know your problem, a lot year ago, one costumer ask me the same cuestion.

The other solution is instaled the monophase transformer, for pole mounting, only for your industry, you need 75 Kva in case of you have one galvanizing machine.

Thanks to dvmdsc hints, I found the solution it is SCOTT connection,

it needs only two single phase transformers, I am now preparing them

check this

http://en.wikipedia.org/wiki/Scott-T_transformer

thanks

using a zig - zag transformer, would that also a possibility ?

I will make some research on this

thanks

I think with a zig-zag transformer you share the load of one phase over two phases.

The magnetic field of the secundairy is made out of the magnetic field from at least two phase of the primairy. And normally a part of the current will then also flow through the thirth phase.

Excuse my ignorance; but, in 40 years of work on three continents I have yet to see a 2 phase AC anything. Electrical load is either three phase or single phase. It can come in a variety of configurations such as two wire, three wire, four wire but it will not be 2 phase.

If you can put an amp meter on the phases you can determine what the load is and connect your SINGLE phase load accordingly. If he actually has a 3 phase load then it is a moot point as you will connect three conductors to three conductors; or, 4 conductors if you are connecting a neutral which I highly recommend if for nothing else but to tie the system neutral to all of your equipment grounds.

Mr Vagabond, It is a single phase load, what the posters refer as two phases, is the output of SCOTT connection, it is two phases in reference to a 3-phases system, with an appropriate transformer ration these two phases voltage will match the voltage of the load

so i can connect my two conductors to these so called "two phases"

Vagabond,

I'm not surprised that you have never seen 2-phase power. It was installed in a few locations 50+ years ago. In single-phase power, with a three-wire service you have two line conductors with the voltages 180-degrees apart and a neutral between them. With 3-phase power you have three line conductors with the voltages 120-degrees apart and often have a neutral either at the star point or on the center between two phase conductors. I'm sure you are very familiar with all the above.

With 2-phase power, you had the voltages 90-degrees apart. It came in different styles--3-wire, 4-wire, and 5-wire; ungrounded or grounded; some were with a neutral while others didn't have one. Different transformer arrangements were used to convert from 3-phase to 2-phase, such as the SCOTT type that has been mentioned on this thread. You can see a reference to 2-phase power in table 430.37 of the NEC; this table has been unchanged from at least 1971 to 2002 (the range in my library).

Because 2-phase used more materials to transmit the same amount of power as 3-phase it never became widely used. I ran into it once about 30 years ago, and don't know if it is still in use anywhere nearby.

And yes, my students in the 4th year apprentice class have asked me how old I was when they discovered electricity. My answer was to tell them that Noah and I had a discussion about this one day.

--JMM

Le Nobel ,Scott transformer gives 2 phase output and you need single phase?

Is it unbalanced load again?

In all cases it will be less unbalanced than full load on one phase

I am trying understand the logic of less unbalanced etc etc. I think you have some time / financial constraint. But the real solution is to have a 3 phase full bridge rectifier diode to covert AC to DC- which is what a galvanising line ultimately needs. I don't think you can find any shortcut. I am trying to see what decision will you take finally.

Replacing the front end of your system with a DC motor drive might be a better solution as:

- It would balance the load across all three phases. The SCOTT connection just moves the load to two phases.

- It would not cost much more than the two transformers required to make a SCOTT connection.

- It would probably be quicker and simpler to install than transformers when overload protection is provided.

- A DC motor drive will be smaller and easier to install that two transformers.

I do not see what that DC motor is going to produce in a e.g. a DC Zink galvanisation that requires a regulated DC supply. I guess, if there are motors involved they will run on the 3 phases. And in my opinion a 2 phase connection can be interpreted as a single phase system too. You are working with 2 "live" connections. While otherwise a live and a neutral. What is there to see the difference?

DC motor drives can be used in applications other than just driving DC motors. Because there are many manufacturers of DC motor drives, they have become fairly inexpensive, at least it is cheaper for a factory to purchase and install rather than design, build, document and maintain a custom solution.

The DC motor drive in this application would be used as a power supply to provide a regulated DC voltage to the process. Only the armature connections would be used. The field connections would not be used. Most DC motor drives have the ability to control both voltage (speed) and current (torque). For a plating operation, I believe that having the ability to control current would be very useful.

I have seen DC motor drives used in a variety of applications such as light dimmers, large solenoid drivers, and etc.

Snave is talking about a dc motor drive, only the drive, not the motor.

Dear ALL

Thank you for all the hints and advises,

the equipment is already installed and running, it includes: a single phase SCR phase switch (voltage chopper, back to back SCR's ) , a step down single phase transformer , than a high current diode bridge.......

the problem is it consume 150AMP from only one phase of our generator, making trouble on the AVR and reducing considerably the available power,

The Ideal solution is, as many suggested, to use a 3 phase bridge , in this case i have to change all the components, use 3 SCR switches, a 3 phases transformer and 3 phases diode bridges , which will cost money and time to be implemented, and plus the operators are already familiar with the existing equipments and can diagnose and repair by themselves, any new equipment will lead to a period of operation instability.....

so the decision is to keep these equipments as they are running fine, and the operators are dealing good with it, and to install an "interface" between it and the 3 phases system.....

SCOTT connection seems to be a good solution the load will be distributed to the 3 phases and need little time to setup...

Le Nobel , what you mean for "AVR" ?

Automatic voltage regulator, for the generator

Le Noble, your load is 32kwatts which is a large load.

What type of transformers you going to use: air cooled or oil cooled ?

I did it many times. It uses 2 transformes connected between the fases. Then the fases will be loaded in the relation 1:2:1. The total capacity of the 2 transformes is a few greather then the total power of 1 phase.

If you informe to me the power and the voltages I can calculate everithing and send to you with a schematic.

By,

Cilmo.

thanks Cilmo

the load is 230vac, 145Amps

generator is 3-phase 230/400v 50hz

It could be much easier and cheaper to buy a new single phase separate generator 230V/150A ,and with time you could find the hydro mains supply (230V) available near to you.

thanks CILMO

Please let us know you final results...

I used an open Delta transformer as described in post 41 by Guest Cilmo ( you?)

the distribution ratio between phases is 1:2:1

the SCOTT transformer give better balance in phases current but the transformers manufacturer said transformers will be too bulky , heavy and expensive.

this solution is acceptable as for rebalance of current on the factory generator THANKS TO THE HELP FROM ALL POSTERS