phase converters HELP
phase converters HELP
(OP)
HELLO ALL, I HAVE A PROBLEM THAT I NEED TO FIGURE OUT BY MORNING. I HAVE JUST REPLACED THE ELECTRIC MOTOR ON MY FORGING HAMMER FROM A 10 HORSE TO A 15 HORSE AND MY PHASE CONVERTER IS A 10 HP. I HAVE ANOTHER 10HP CONVERTER THAT IS NOT BEING USED. I HAVE HEARD THAT YOU CAN USE THE TWO TOGETHER TO GET MORE HP. BUT DO NOT KNOW HOW. I BELIEVE THAT YOU CAN WIRE THE OUTPUT IN PARALELL AND THAT IS ALL THAT IS NEEDED BUT DO NOT KNOW ENOUGH TO TAKE THE CHANCE OF BLOWING TWO CONVERTERS UP. WE ARE FILMING MYSELF (THE BAREFOOTBLACKSMITH), MY 11 YEAR OLD DAUGHTER (THE BLACKSMITHETTE), AND HERMAN ( THE 100 YEAR OLD FORGING HAMMER)FOR A SHOW ON OLD TOOLS WED MORNING AND NEED THIS HAMMER UP AND RUNNING. ANY HELP IS APPRECIATED. THANX AGAIN, THE ANARCHIST





RE: phase converters HELP
Another forum, www.practicalmachinist.com has people with a lot of practical experience in rotary phase converters (RPCs) as well, you may want to ask in there.
Barefoot? OUCH!
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: phase converters HELP
Assumption #1. The phase convertors are standard three phase induction motors with enough capacitors between two phases to give enough phase shift for the motor to start on single phase and then produce the three phase running as an induction generator.
Assumption #2. The phase convertors are identical. Not just externally, but the wiring connections are identical internally also.
Assumption #3. The leads can be identified, and matched from one machine to the other.
If we meet all these criteria, we can probably connect the machines in parallel.
Starting both convertors together will be a challenge. You can probably start one and then the other, then start "Herman". Don't forget to check the wire size going to Herman to be sure that it is adequate for 15 HP.
Wait for a few other experts to respond and consider all the advice.
yours
RE: phase converters HELP
RE: phase converters HELP
In that other forum there is also a gentleman with the handle peterh5322 who has a really good handle on designing and building RPCs from scratch. I strongly suggest posting there and specifically asking for his input.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: phase converters HELP
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: phase converters HELP
Check with the other forum. It is a fairly involved process and possibly dangerous to try to match the phase rotation on two disimilar units. Better to get advice from someone who works a lot with rotary phase converters.
Good luck
respectfully
RE: phase converters HELP
RE: phase converters HELP
I agree with you, but without being on site to check loading and balances on both the phase converter and the 15Hp. motor, I hesitate to give possibly bad advice. If either you or I was on site, we would probably not have a problem but I think it's more professional to refer our poster to the people who work with Rotary converters frequently.
A lot depends on the load on the "Hammer named Herman". I imagine the load will be cyclic and determining the actual RMS horsepower may be difficult. Another big factor will be whether the 15 HP has the same torque characterestics as the original 10 Hp. motor.
As I understand a phase convertor, it works as an induction generator to supply the current for the third line. If you can get the 15 Hp. motor started and the load is light enough that it draws the same or less current than a 10 HP. motor it will probably work fine. However, if a high slip motor is replaced with a low slip motor all these nice assumptions go out the window.
Like you, I hate to back away from a problem, but in this case I think I'm going to just "lurk" for awhile and see what new stuff I can learn.
PS, Let us now how the movey shoot goes please, anarchist
respectfully
RE: phase converters HELP
I was imagining a big flywheel being kept at speed so once it reaches speed the motor does nothing most of the time and grunts briefly after each blow. But as you point out without seeing it I could be way off. Furthermore the original acceleration of the flywheel could be very problematic because the bigger motor will try to do it, (I presume), faster. And this may stall the whole operation creating more smoke then can be attributed to the forge alone.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: phase converters HELP
These are rotary phase converters, so they will start up and run in either direction, so phase rotation is not really an issue. If you feed one with two 120 degree phases, it automatically generates the missing third phase, just like a Scott T transformer would.
I would connect up both rotary converters to the source and start them up. Then measure the output voltages between the phases of both machines (one machine to another).
The two incoming phases will correspond exactly to two of the output phases, so they can be safely paralleled. The third generated "phantom" phase will differ slightly in voltage and phase between machines, but it should still be safe to parallel them if the voltage difference is only a few volts.
RE: phase converters HELP
If you have two phases at 120 degrees, you don't use a rotary converter, you use an open delta transformer connection, or a Wye-zag connection.
My understanding of a rotary phase converter is that it converts single phase to three phase. It is basically a three phase motor running single phased. The capacitors create a phase displacement to get it started and then act to help supply some of the energy for the third phase, and some of the magnetizing current. The rotation of the resulting field depends on the internal connection of the capacitors. And their values.
Some convertors use a manual starter and some use power factor correction capacitors in addition to phase shift capacitors.
The rotation of the motor shaft is unimportant, but if the rotation of the magnetic field is reversed in one converter in relation to the other converter you can get a voltage between the two third legs in the order of root three times line volts. That would be over 400 volts with a 240 volt supply.
Another factor; I understand that one of anarchist's phase convertors is a homebrew model. The alternate technology people, possibly on the principle that more is better, often connect a second set of capacitors from the second line to the third line. The second set of capacitors balances the first set with no net phase shift but often a very good power factor. They must then add a third set of capacitors to unbalance the first two sets and get the phase shift they need to create starting torque. Once the converter is running, it is an induction generator. It now produces three phase power despite the efforts of the capacitors. I imagine that the extra capacitors do help correct the power factor of the driven motor and so reduce the line current somewhat. The point is that paralleling different phase convertors may be more involved than just starting them and connecting them together.
respectfully
RE: phase converters HELP
If the voltages coming out of each machine are identical, paralleling them is never going to be a problem. If they are radically different, because of either voltage or phase difference in the third leg, it would probably not be safe to connect them together. Two output legs are always going to be direct hard connections to the source.
I just proposed this as a very quick and simple test to see if parallel operation was feasible.
RE: phase converters HELP
Use the RPC that starts the best as the first to start,
then start the second RPC using the motor and contactor
only (from the second RPC). This will give you a 20HP
converter which should start your 15HP machine (unloaded).
It will not be as balanced as it would be if all the caps
were used (assuming both converters were balanced in the
first place), but should be sufficient for your task.
It is highly unlikely that the combination was balanced
for a 15HP load (7.5 + 7.5) anyway. Rotation is unimportant.
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RE: phase converters HELP
RE: phase converters HELP
respectfully
RE: phase converters HELP
RE: phase converters HELP
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com