Single to 3 Phase Converter Problem

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gk351

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I have a customer who is in a rural area and 3 Phase power was not a viable option($50,000+). So he thought that a 3 phase converter would work. They had the system installed by another contractor. The system runs a CNC Machine, dust collection system, and vacuum pump. The equipment is all European designed to run on 380V. They have a phase converter,and transformer that steps up from 240V to 480. With no load, they have a constant voltage around 473, 478, 490 per each phase. When everything is started, the system loses at least 100V per phase. The equipment will stay running, but it causes some problems with the CPU in the CNC machine. Anybody have any ideas about the voltage drop of this proportion?
 
You need a better phase convertor. My preference for new generation (<10yr old) 'CNC' machines have been digital ones.
 
100921-1604 EST

Something is fishy.

Are there 3 single phase transformers used to step up the voltage? Are they connected delta to delta, or what? I will assume delta to delta.

The two single phase hot wires that are the input to the phase converter simply pass thru to the output. Therefore, with in reason, how bad the voltage to the generated third phase hot wire is, should not impact the voltage between the original two input lines as seen at the output.

Internal to the CNC I would expect a transformer at the input with taps to provide a means for adjusting for some variation in line voltage. But, you should not feed a 380 machine with 480. This is a real big problem.

Provide much more information on the internal circuitry of the CNC relative to input voltage.

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Thanks for the replies. There is 240V Single phase that is both sent to a contactor for the phase converter, and another line of 240V Single phase sent to another contactor for the transformer. When the turn the system "on"...the start button energizes the coils of both contactors. This starts the phase converter. Inside the 240/480V Delta Dry pack transformer, you have the the two wires that come from the transformer contactor that feed the Secondary connections, aka X1 & X2. There is 1 wire coming from the phase converter, it is attatched to the X3 connection. I will call the true secondary connections the 48oV connections ( H1, H2, H3) because they are feeding the tranformer backwards of what it was originally desgined. When I have no load, I have somewhat regular voltage, 472, 478, 490. When I start the vacuum pump, my voltage drops to 380 or so and stays there. With that running, I start the dust collector, my voltage drops to 280 +/-, but recovers to 380V +/- after 5 seconds or so. The CNC machine won't start at this point...not enough voltage. So they start the CNC first, and then the others. The problem is when you start the other equipment, the CNC machine throws a fault and has to be reset. They would prefer to shut the dust collector off multiple times per day. It just gets annoying restting the machine 20-30 times daily. Yes the equipment was designed for use in Europe. I'm still not even sure how it all works. the motors are internally wired for 415V Delta.

Like I stated in my first post....I DIDN'T install this system. I'm helping to find solutions to the problem. The contractor who installed it won't return there phone calls....go figure. Thanks everyone!
 
Ugly solution - get into the CNC machine and repower the electronics from 120V line. I'm guessing as theese are Machines of Eurpoean Origin then listing (and violating it by rewiring a machine a bit) isn't seen to be an issue.

In the bigger picture, those voltage drops look excessive, and make me think that there is a fundemental issue with an inadequately specified converter thing, which includes the transformer.

Does the 240V supply hold up when all this stuff is running?
 
I think I'd recommend a VFD, if not three of them.

I can't help but wonder about the 240v 1ph current.
 
As soon as I got home I realized I didn't even think to check the 240V side of things. Thats will be my quest tomorrow. The guy who put in the service, he did run 2/0 Copper for the 480V 200Amp Panel. Thats a violation, but I don't think it directly relates to the massive voltage drop. The transformer is a 75KVA 480/240 Delta. The rotary converter is blocked, and I can't get a view of the dataplate. (They built a shack around everything, and stuffed it with junk and other things. Thanks everyone.
 
I got a question that may change some answers.

Is the phase converter a static or rotary?

will this CNC work on 60hz? you know it will run faster and it might also throw the servos off if there is no headroom on the speed controls.

the voltage drops your getting to me sounds like a wrongly used static converter.
You can use a static but you will need to use a 3-phase pony motor that is at least 2x your largest motor, but I don't suggest this on a CNC as the phase voltage will not be very balanced.

Also starting the transformer and converter at the same time is not a good idea, bring each one line one at a time.

What is the calculated HP of the load, and phase converter?
 
The problem is not with the phase converter. If it were, the drop would occur only on the generated leg. However, it is occurring even to the non-generated legs.

My immediate assumption was the transformer was undersized causing the voltage drop, but when the OP commented about the single-phase feed to this system, I realized that this is also a very likely cause. A 2/0 feed should not be resulting in the voltage drop, but a poor connection of the 2/0 would. As a matter of fact, since the transformer does not appear to be undersized, a poor connection on the 3-phase side would not produce voltage drops across all three phases, but a single poor connection on the single-phase side would cause a voltage drop across all three phases.

Check your single-phase lugs.
 
Rick Christopherson said:
The problem is not with the phase converter. If it were, the drop would occur only on the generated leg. However, it is occurring even to the non-generated legs.

My immediate assumption was the transformer was undersized causing the voltage drop, but when the OP commented about the single-phase feed to this system, I realized that this is also a very likely cause. A 2/0 feed should not be resulting in the voltage drop, but a poor connection of the 2/0 would. As a matter of fact, since the transformer does not appear to be undersized, a poor connection on the 3-phase side would not produce voltage drops across all three phases, but a single poor connection on the single-phase side would cause a voltage drop across all three phases.

Check your single-phase lugs.
Click to expand...

The phase converter is ahead of the transformer, and OP only checked the output of the transformer, see post 10;)
 
hurk27 said:
The phase converter is ahead of the transformer, and OP only checked the output of the transformer, see post 10;)
Click to expand...
I know that.
gk351 said:
...With no load, they have a constant voltage around 473, 478, 490 per each phase. When everything is started, the system loses at least 100V per phase.
Click to expand...
Either the original poster mis-spoke, or he is seeing a voltage drop between each of the output phases. If he mis-spoke and the voltage drop is only at the generated leg, then yes, I agree that the problem is with the converter. However, if he is in fact seeing a voltage drop "per phase", then the converter is not the problem.
gk351 said:
Inside the 240/480V Delta Dry pack transformer, you have the the two wires that come from the transformer contactor that feed the Secondary connections, aka X1 & X2. There is 1 wire coming from the phase converter, it is attatched to the X3 connection.

When I have no load, I have somewhat regular voltage, 472, 478, 490. When I start the vacuum pump, my voltage drops to 380 or so and stays there.
Click to expand...
A and B phases are shore power and the converter has no bearing on their voltage. C-phase comes from the phase converter.

If all three voltage readings are dropping by 100 volts, then the most likely cause is at the single-phase side of the system (assuming the transformer is not undersized).
================================

However, after giving this a few more reads, I understand that he could have been referring to Vca and Vcb as dropping, but not Vab. If this is what he meant, then I agree that the problem is at the converter.

Given that assumption and given the drastic voltage drop with only a slight load, then the first thing I would look for is whether this phase converter even has the basic run-capacitors. Clearly it would have the required start capacitor, but without the run capacitors, the voltage will drop like a rock when a load is applied. This would indicate that the RPC is home-made based on the misconception that simply dumping a 3-phase motor into a circuit constitutes an RPC.

If this is the case, then the RPC can be repaired by adding the appropriate balancing capacitors across A-C and B-C legs. Adding these capacitors will probably be cheaper and easier than replacing the home-made RPC with a pre-fab RPC.
 
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