Delta 3 Phase Center Grounded

[Craigpor]

Hello Everyone,

I was wondering if someone may have experience dealing with 3 phase 240 volt systems
We are currently wiring a printing press. My client got this press out of a different plant in another state. The electrical contractor at the plant where it came from gave me the power requirements for the printing line. I was told that the press required 240 volt , 3 phase , center grounded. There are a few other parts of the press that require power but the loads are mainly 240 volt , 20 amp and 30 amp , 3 phase , center grounded. The plant where the press came from had 480 volt power.
The plant that I work in has only 3 phase, 208/120 volt Y. My local supplier of transformers supplied us with an isolation type dry transformer, 75 KVA. The transformer goes delta 208 to delta 240. The main 100 amp feed to the press goes to a disconnect then to 3 dry type transformers that step the voltage from 240 to 380. On the line side of the disconnect the wires are red, black white, red and green. On the load side the wires are brown orange yellow , white and green.
I am trying to figure out how to achieve center grounded 240 Volt? Or do I just feed it 240 Delta?

 

[ron]

Grounded supplies are more stable. You might want to ask the other plant electrician to measure voltages at the terminals to see if it is really center grounded or maybe corner grounded delta.

Center grounded usually means that the middle of one winding is grounded. High-leg delta (also known as wild-leg, stinger leg, bastard leg, high-leg, orange-leg, or red-leg delta) https://en.wikipedia.org/wiki/High-leg_delta

I would think you would need a three phase delta transformer designed for this, or use the individual transformer method mentioned in the wiki article.

Other types of three-phase supplies are wye connections, ungrounded delta connections, "ghost" leg configuration delta connections (two transformers supplying three phase power), or corner-grounded delta^[2] connections. These connections do not supply split single-phase power, and do not have a high leg.

 

[kwired]

Hello Everyone,

I was wondering if someone may have experience dealing with 3 phase 240 volt systems
We are currently wiring a printing press. My client got this press out of a different plant in another state. The electrical contractor at the plant where it came from gave me the power requirements for the printing line. I was told that the press required 240 volt , 3 phase , center grounded. There are a few other parts of the press that require power but the loads are mainly 240 volt , 20 amp and 30 amp , 3 phase , center grounded. The plant where the press came from had 480 volt power.
The plant that I work in has only 3 phase, 208/120 volt Y. My local supplier of transformers supplied us with an isolation type dry transformer, 75 KVA. The transformer goes delta 208 to delta 240. The main 100 amp feed to the press goes to a disconnect then to 3 dry type transformers that step the voltage from 240 to 380. On the line side of the disconnect the wires are red, black white, red and green. On the load side the wires are brown orange yellow , white and green.
I am trying to figure out how to achieve center grounded 240 Volt? Or do I just feed it 240 Delta?

Can you give us a model number or pictures of connection diagrams?

If your 240 volt secondary only has three terminals, you likely don't have a mid tap available to ground. You can only corner ground it or run it ungrounded if that is the case. Mid tap is usually designated X4 on those systems.

If your machine doesn't have any 120 volt loads (or has it's own internal 120 volt control source) you still may be able to supply it with corner grounded supply though.

 

[ptonsparky]

To late now, but a couple buck/boost xfmrs would have been a lot less hassle and expense.

 

[Craigpor]

Delta

Delta

Can you give us a model number or pictures of connection diagrams?

If your 240 volt secondary only has three terminals, you likely don't have a mid tap available to ground. You can only corner ground it or run it ungrounded if that is the case. Mid tap is usually designated X4 on those systems.

If your machine doesn't have any 120 volt loads (or has it's own internal 120 volt control source) you still may be able to supply it with corner grounded supply though.

Thanks for help, I do not have any connection info for the press- it is very old. The only loads getting power off the delta system are the three phase 240 volt loads and a single phase 240 volt load. I am pulling 120 volt power from a different source panel. I have set up a panel for just the delta 240 volt loads.
I do not recall seeing an x4 tap how do corner ground?
Thanks

 

[ptonsparky]

Thanks for help, I do not have any connection info for the press- it is very old. The only loads getting power off the delta system are the three phase 240 volt loads and a single phase 240 volt load. I am pulling 120 volt power from a different source panel. I have set up a panel for just the delta 240 volt loads.
I do not recall seeing an x4 tap how do corner ground?
Thanks

The xfmr may have a dotted line to one corner of the secondary. Bond that one to building steel, electrodes, water pipe etc. You might want ensure that is what you want to do. Volt to ground will now be 240.

 

[ActionDave]

Thanks for help, I do not have any connection info for the press- it is very old. The only loads getting power off the delta system are the three phase 240 volt loads and a single phase 240 volt load. I am pulling 120 volt power from a different source panel. I have set up a panel for just the delta 240 volt loads.
I do not recall seeing an x4 tap how do corner ground?
Thanks

I have to belive there is someone coming in to commission the press. Have you talked to him? He is going to be the best guy to tell you if the transformer you have will work. It may in fact be just fine as a corner ground but you need to know what he is going to say about it.

 

[Craigpor]

Delta

Delta

How could I make sure the machine is really center grounded? It is odd that the transformers that go 240 to 380 have a neutral coming out on the high voltage load side.

 

[kwired]

How could I make sure the machine is really center grounded? It is odd that the transformers that go 240 to 380 have a neutral coming out on the high voltage load side.

Kind of missed that 380 volt in OP. Does all of the machine run off this 380 volts or just portions of the machine?

Sounds like it is maybe imported equipment? 380/220 wye systems, are common outside of the US. As time has gone by the evolved to 400/230 and 416/240 similar to how systems in the US evolved from 440 to 460 to 480 or 110, 115, 120 as a widely utilized nominal voltage.

If all of the machine runs off that transformer then for the most part all you need to do is make sure you have 240 input to that transformer. It won't care what is grounded and what is not grounded to work, to comply with code you will need to pay attention to what is grounded and what isn't though, but you do have some options. As mentioned earlier a couple of buck boost transformers would likely have been the easiest and least costly way to do that.

 

[ptonsparky]

How could I make sure the machine is really center grounded? It is odd that the transformers that go 240 to 380 have a neutral coming out on the high voltage load side.

Are these the transformers that came with the machine? Are you meaning 380 or 480? I see you have typed it a couple times.

 

[Craigpor]

Delta

Delta

Yes the machine is European. The transformers came with it. There are (3) dry type transformers that go from 240 to 380. This is for the main 100 amp feed to the press. There are ink dryers that I am told are 240 volt , 3 phase center grounded, 60 amp.
Thanks

 

[ptonsparky]

Yes the machine is European. The transformers came with it. There are (3) dry type transformers that go from 240 to 380. This is for the main 100 amp feed to the press. There are ink dryers that I am told are 240 volt , 3 phase center grounded, 60 amp.
Thanks

IDK but I think that will throw another twist into things.

 

[zbang]

I'm very suspicious of this kind of thing- sounds like you need to actually see the equipment, read any info plates, and maybe even trace some wires.

Might be that the previous install was a bit of a hack and you can un-do some of that at it's new home.

 

[ActionDave]

...If all of the machine runs off that transformer then for the most part all you need to do is make sure you have 240 input to that transformer. It won't care what is grounded and what is not grounded to work, to comply with code you will need to pay attention to what is grounded and what isn't though, but you do have some options.

I agree for the most part. Thing is there are people that work on these presses for a living. That's the guy you want to talk to.

As mentioned earlier a couple of buck boost transformers would likely have been the easiest and least costly way to do that.

No. No buck/boost. I have not worked on a lot of presses so I do not fell comfortable giving a lot of advice about them but my experience has been isolation transformers are SOP for changing voltage from 208 to 240 or even going from 240 to 240 then on to the machine.

 

[ActionDave]

I'm very suspicious of this kind of thing- sounds like you need to actually see the equipment, read any info plates, and maybe even trace some wires.

Might be that the previous install was a bit of a hack and you can un-do some of that at it's new home.

There is nothing the op is describing that sounds hacked at all. It all sounds very normal. He just needs to know if he can feed the unit with a corner ground transformer or not.

 

[Craigpor]

There is nothing the op is describing that sounds hacked at all. It all sounds very normal. He just needs to know if he can feed the unit with a corner ground transformer or not.

Thanks for the info.
I just want to make sure the press is safe and that I do not mess it up by providing the wrong power source.

 

[ActionDave]

Thanks for the info.
I just want to make sure the press is safe and that I do not mess it up by providing the wrong power source.

Your welcome. Like I said I'm not sure you can feed it with a corner ground but that should not be hard to find out. Corner grounds are not that hard they are just weird because they are rare. I'd be looking into getting a center tapped delta secondary if it is an option, you'll get less head scratching throughout the project.

The transformers on the press itself should all be wired the way the manufacturer wants it.

 

[Barbqranch]

Why don't you ask the electrician at the plant the press is coming out of to measure the voltage from each wire to ground. That will tell you what you want to try to emulate.

 

[Jraef]

Yes the machine is European. The transformers came with it. There are (3) dry type transformers that go from 240 to 380. This is for the main 100 amp feed to the press. There are ink dryers that I am told are 240 volt , 3 phase center grounded, 60 amp.
Thanks

I'm very suspicious of this kind of thing- sounds like you need to actually see the equipment, read any info plates, and maybe even trace some wires.

Might be that the previous install was a bit of a hack and you can un-do some of that at it's new home.

I agree with zbang. I've done a lot of reworking systems to accommodate European machines and people make a LOT of mistakes with his, not understanding it fully before just slapping in transformers. This may very well be one of those situations, it needs more thorough investigation to ensure you are not wasting time and money duplicating a previous mistake and making it even worse by now trying to adapt it to you new different system. You could be ending up doing a hack to feed a hack.

From the sounds of it, the machine was likely designed for European 3 phase 380V 50Hz power. Someone brought it here and needed to connect it to 240V 3 phase, so they ran out and bought 240-380V transformers, not understanding that by giving the motors 380V 60Hz, they were risking damaging them (or they understood, but didn't care). Then they had ink heaters that were, for the European system, connected as 220V single phase by using Line to Neutral (star connection) on each one, but that would be based on a 380V WYE (Star) service (because that's all they have there). So most likely that custom transformer that you have is a 240V delta to 380V WYE system with a grounded neutral.

Yes, you COULD just leave that in and buy ANOTHER transformer to boost your 208V wye to 240V delta, then keep using that 240V delta to 380V wye, but that's a hack on a hack. In addition, as mentioned earlier, it gets MORE complicated because your 240V delta from the new transformer to the 240V delta input of the OLD transformer will need to be either a corner grounded delta or have ground fault detection on it. A corner grounded delta system may have unforeseen effects on anything electronic in this press, and having to add GFP will add even MORE cost and complexity.

Then, most likely if there are 3 phase motors in this printing press, they have been running too fast and too hot for years because they have been getting 380V 60Hz. That's because the motor available torque will have been reduced to roughly 62% of normal while at the same time, the speed is 120% of normal, resulting in them running at high slip and pulling more current than necessary. Those motors may be on their last legs by now. In reality, if they had simply connected them to 480V, they would have provided full torque and although still run 120% faster, at least they would not be stressed out. Motors provide torque and speed, the result of which we call "horsepower" (they call kW, as in mechanical kW). The rated torque of a motor is based on the design voltage and frequency, the "V/Hz ratio". As long as you remain within +-10% of that V/Hz ratio, the motor provides full torque and is happy doing its job. Speed is determined by the frequency and number of poles, so applying higher frequency means higher speed. A motor designed for Europe was made as 380/50, so a V/Hz ratio of 7.6:1. If you feed it 480V 60Hz, the V/Hz ratio is 8:1, well within the 10% tolerance. If you however feed it 360/60 as they likely did, the ratio becomes 6:1 which is 79% lower than what the motor was designed for and since the torque is changed by the SQUARE of that value, the motor torque capability drops to 62% of normal. Adding another layer of transformer to this will drop the voltage and make things even worse in this aspect.

The other possibility is that the Printing Press has all DC drives and motors. If that's the case, then the DC drives, if designed for 380V input, may not care at all about input frequency because it just rectifies it. If so, you will need 380V to feed them then, but rather than a transformer to a transformer and all the rigamarole of a delta system feed I would just go out and get a 208V delta to 380V wye transformer and have only one unit, no need for GFP or corner grounding, etc. Simple is better. The heater circuits would need to be rewired, but running them on 208V (line to line now) will just result in them taking a little longer to get to temperature.

So back to the earlier premise; this begs for not taking the easy way out and just piling on another hack to feed the previous hack. get the data ahead of time and do it right, probably for the first time.

 

[Tony S]

From the sounds of it, the machine was likely designed for European 3 phase 380V 50Hz power. Someone brought it here and needed to connect it to 240V 3 phase, so they ran out and bought 240-380V transformers, not understanding that by giving the motors 380V 60Hz, they were risking damaging them (or they understood, but didn't care). Then they had ink heaters that were, for the European system, connected as 220V single phase by using Line to Neutral (star connection) on each one, but that would be based on a 380V WYE (Star) service (because that's all they have there). So most likely that custom transformer that you have is a 240V delta to 380V WYE system with a grounded neutral.

We had both printers and foil converters manufactured in Belgium/Germany. They stipulated the supply to the machines had to be 380/220V otherwise they wouldn’t issue a warranty. UK voltage is 433/250V

A new DNO (PoCo) supply to a 1500kVA 11/0.38kV transformer along with new switchgear and bus trunking had to be installed.

As JR said most of the drives will be fed from inverters, where the problem comes is the ancillary equipment.