three phase wye motor, only delta available

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gmreynol

gmreynol

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We have a customer who has received a machine that must be connected to a 3 phase supply which has 120 volts on each phase, I assume a wye system. The building is equipped with a Delta system, 240v high leg... The manufacturer is saying all he needs is 120v on each leg. He suggests using A and C phase since they are already 120v, and to acquire 120 volts on B phase, connect two of the phases, i.e. A&B or A&C to a step down transformer. Will this application work, why or why not?
 
Re: three phase wye motor, only delta available

Ummm...ask the manufacturer which configuration will NOT void his warranty.

IMO, a 240 X 208/120y xfmr will avoid a lot of potential problems.
 
Re: three phase wye motor, only delta available

I believe one of the possible concerns for the high leg is the controller itself.
 
Re: three phase wye motor, only delta available

Our foreman on this job suggest using a delta to wye transformer which may cost a grand where the manufactures solution may cost a few hundred dollars, If the manufacturere puts it in writing to do this, what is the risk? Will it even work?
 
Re: three phase wye motor, only delta available

Are there any three phase motors on the machine, because with what you discribe, i dont see how you can keep your phase angles alligned.
 
Re: three phase wye motor, only delta available

I seriously doubt the manufacture's suggestion will work. If you look at a triangle as the symbol of a delta-connected system, the A & C phases are the same, straight line vector, the base of the triangle. The grounded conductor is mid way between the two phases, 180 degrees apart. A wye-connected system requires the phase-to-neutral voltage to be 120 degrees apart.

Imagine drawing a circle around the delta symbol, with the circle touching the corner of the triangle. In a delta-connected system, the 120 degree separation is from phase to phase. In a wye-connected system the 120 degree separation is from both phase-to-phase and phase-to-neutral.

If somebody can draw a picture of this, it may be clearer.

MKB
 
Re: three phase wye motor, only delta available

Originally posted by gmreynol:
If the manufacturere puts it in writing to do this, what is the risk? Will it even work?
Click to expand...
You fail to mention what this machine consists of. If it is simply motors, the solution can be simple. However, if there are sophisticated electronics, inverters, etc, the solution can be complicated.
OTOH, when the mfr sold you the machine, did he ask for the available site power configuration? Could he have furnished the machine to match your power? If not, did he inform your company of the problem at the time of purchase?
Seems to me that if it will cost you a grand for the solution (plus labor), he should be willing to help with the cost if he was negligent in some way in the sales presentation. :D
 
Re: three phase wye motor, only delta available

Sometimes you have to get the salesman off the phone and talk to an engineer.

I have seen machines that could simply have seperate 120vac run for the computers and then would work fine on the delta 240volt. Took a little rewireing in the control cabinet.
 
Re: three phase wye motor, only delta available

yes it does have a three phase motor and I believe a variable speed drive, and electronics... its a conveyor system. I agree the manufacturer should eat some of the cost or convert it to run on a delta system. Either way it all pays the same, we are just trying to keep a happy customer for the future. I,m just curious if it would run at all, and if so, how long?
 
Re: three phase wye motor, only delta available

without knowing a lot more about what is exactly in the machine, it is almost impossible to tell from here.
 
Re: three phase wye motor, only delta available

It is unlikely that the three phase motor is 120V line to line. So what line to line voltage does it really need?

Some where there is a communications disconnect. You need to get a wiring diagram not a verbal description from the manufacturer.

In the US the only three phase 120V system you can get easily is 208Y/120 three phase four wire. The only way to get this from a 240V supply system is with a three phase transformer arrangement.
 
Re: three phase wye motor, only delta available

It puzzles me why vendors and OEM's don't get the operating voltages for the facility that they're building equipment for squared away on day one of the design process. This is a screwup that we see on too regular of a basis.
 
Re: three phase wye motor, only delta available

Putting the controller aside, the motor is 230 volt three phase. There is no problem with phase A and C, each at 120 volts and 240 volts beween the phases. The question is what will the new stepped down B phase test at between A or C. Correct me if I am wrong but a three phase motor will run missing one phase. Will the new B phase angle be close enough to run the motor but not at its maximum efficiency or capacity?
 
Re: three phase wye motor, only delta available

If you have a 240/120V 3phase 4wire delta system (high leg), then AB=BC=CA=240V. Your motor will run fine.

If the control circuits in your panel are 120V 1phase 2wire then they need to be connected AN or CN.

It sounds like someone is trying to solve a problem that does not exist.

And no, you should not run a fully loaded 3phase otor on single phase.

[ December 13, 2005, 10:13 AM: Message edited by: jim dungar ]
 
Re: three phase wye motor, only delta available

Let me add to my above post for clarity.
The machines I am talking about spec a 120/208 wye feeder. In reality the only thing the neutral is being used for is 120 control or computer circuits. Because of the internal wireing of the machine, a high leg would cause a problem.

We were able to rewire the control circuits that were on the B phase to a seperate 120v circuit.

In retrospect a 240v single phase to 120v control transformer should have worked as well.
 
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