240 3ø totally confused...

[TRM0002]

In the original report you said 128,128,0 L-G and 240, 240, 240 L-L.

What are you now reading as 240/0/240?

Jon

My bad. You are correct 128/0/128. I was in a hurry running out the door to at least post a quick update on what I found. I was just highlighting that the whole issue was that the center leg was indeed dead starting right at the main FP 480/240 transformer.

 

[winnie]

My bad. You are correct 128/0/128. I was in a hurry running out the door to at least post a quick update on what I found. I was just highlighting that the whole issue was that the center leg was indeed dead starting right at the main FP 480/240 transformer.

Hmm. Where did you measure 240/240/240 L-L?

The machines that you say are still working...were they ever stopped and restarted?

Could you get a complete set of measurements (L-N, L-G and L-L) at the transformer? (L-N meaning L-X0 at the transformer terminals, L-G meaning transformer terminal L to convenient ground lug).

-Jon

 

[TRM0002]

Hmm. Where did you measure 240/240/240 L-L?

The machines that you say are still working...were they ever stopped and restarted?

Could you get a complete set of measurements (L-N, L-G and L-L) at the transformer? (L-N meaning L-X0 at the transformer terminals, L-G meaning transformer terminal L to convenient ground lug).

-Jon

Yes- still measured 240 L1-L2, L2-L3, and L1-L3. And yes, those older lathes and the jigbore were shut down and turned back on daily. The much newer CNC Haas mill went down last week but the first thing we noted was no power output from the 240/12VDC transformer in the machine. All we did at that point was confirm the 240 across the incoming legs (not each leg to ground) and that LOOKED good. So we ordered another 240/12 transformer and had to wait for it to arrive. When it did arrive yesterday and we still had no power output from that new (certified used) one, that's when we started to dig deeper.

 

[Krusscher]

Yes- still measured 240 L1-L2, L2-L3, and L1-L3. And yes, those older lathes and the jigbore were shut down and turned back on daily. The much newer CNC Haas mill went down last week but the first thing we noted was no power output from the 240/12VDC transformer in the machine. All we did at that point was confirm the 240 across the incoming legs (not each leg to ground) and that LOOKED good. So we ordered another 240/12 transformer and had to wait for it to arrive. When it did arrive yesterday and we still had no power output from that new (certified used) one, that's when we started to dig deeper.

What happens when you shut the disconnect off after the transformer? I am assuming you are only reading 240 line to line on all phase because it is back feeding through a motor. If you shut the main after the transformer off one of those line to line readings should go away of a phase in the transformer is dead. I may be wrong because you should still read that to ground... maybe it's too early and I need more coffee.

 

[winnie]

240V L1-L2, L2-L3 and L1-L3 with 128V L1-G, L3-G and 0V L2-G . Did you also measure L-N _at the transformer_?? Does the transformer have a neutral?

The older machines are three phase motors, not single phase motors tapped off of 2 legs?

If the transformer has failed and is no longer producing 3 phases, then it couldn't start a 3 phase motor spinning. (Note: an already spinning 3 phase motor that loses a supply phase can keep spinning, and if lightly loaded will function just fine. It can even act as a RPC and generate the missing phase for other loads. This is why I asked if the older equipment was stopped and restarted.)

If you have a solid 3 phase 240V, then getting the 128V measurements requires some sort of neutral, but not at the strict neutral point of the system. A solid 240V single phase neutral would give you 120V (with 208V to the high leg), a solid 3 phase neutral would give you 139V.

I am sticking with my hunch that the transformer is now no longer properly bonded to ground, if it ever was. On top of this I think you have a L-G load connected.

-Jon

 

[Joethemechanic]

If the transformer has failed and is no longer producing 3 phases, then it couldn't start a 3 phase motor spinning.

What if those motors were on VFDs? Single phase rectified feeding the DC bus.

 

[ptonsparky]

What if those motors were on VFDs? Single phase rectified feeding the DC bus.

Dependent on the parameter settings and size of the VFD. Some will.

 

[winnie]

What if those motors were on VFDs? Single phase rectified feeding the DC bus.

The op described a machine with VFD faulting, other older machines working just fine, implying they are not using VFDs.

Yes, suitable VFDs can work with single phase input.

Jon

 

[TRM0002]

For what it's worth, I was told the jigbore power was for sure never shut off at the breaker (it does not have an on/off button or switch)- keeping in mind that doesn't mean the motor was always engaged and running- just that the breaker power to the machine was never shut off. They did however tell me that the two lathes were indeed turned off and back on but only at the on/off panel switches and never at the breakers. Oddly, Friday morning one of the two would not run but the other one did; so I'm REALLY confused now.

As for the 128V mentioned by Winnie, we simply ran the Fluke ground to the ground strip in the 480V box sitting right next to and feeding the transformer and then checked power at the three transformer leg outputs. Of note, there is power at all the INCOMING taps including on the "bad" transformer leg at the top of each coil.

 

[ptonsparky]

For what it's worth, I was told the jigbore power was for sure never shut off at the breaker (it does not have an on/off button or switch)- keeping in mind that doesn't mean the motor was always engaged and running- just that the breaker power to the machine was never shut off. They did however tell me that the two lathes were indeed turned off and back on but only at the on/off panel switches and never at the breakers. Oddly, Friday morning one of the two would not run but the other one did; so I'm REALLY confused now.

As for the 128V mentioned by Winnie, we simply ran the Fluke ground to the ground strip in the 480V box sitting right next to and feeding the transformer and then checked power at the three transformer leg outputs. Of note, there is power at all the INCOMING taps including on the "bad" transformer leg at the top of each coil.

What did you measure to determine you had line side power? Don't use line to equipment ground, line to neutral or line to earth.

Your newer CNC may use those references for whatever purpose, but the older ATL motors do not.

 

[ActionDave]

I am confident Buffalo has an electrician who is competent to help you resolve this problem. Time to close this thread.

 

[Jraef]

My guess here (albeit a closed thread) is that it is / was a 240V corner grounded delta system, but because there are CNC machines they likely have VFDs and Servo amps with MOVs on the front-end rectifiers. Those MOVs are almost always configured in a Wye referenced to ground, so if connected to a delta system, you are supposed to disconnect the ground reference, otherwise they fail catastrophically if there is any kind of ground fault. If that was not done (because nobody reads instructions), he now has a corner grounded delta system with MOVs that have failed, giving him strange readings.

A simple test of this theory would be to disconnect power to any and all CNC machines or other power electronics and see if the voltage readings remain odd.