Neutral Floating from a transformer wye to Delta 2

[Zanana]

I have 380 volt from a transformer going to a big panel for controlling machine.
input to this panel 4 wire (3+neutral)

the neutral is floating as the transformer is wye to delta and the panel designed to work with wye.

the problem some breakers on the panel does not work correctly as some button and switchs work with 220volt from the panel (the panel are capable of supplying this button with 220 volt).

they told me that's because the neutral is floating and u have to got an additionnel transformer from 380 volt to 220 volt to got the right neutral to your buttons .
but I know there is another solutions ,
Note; all the machines 380 volt working with no problems the problems is the fans at 220 volt does not work correctly.

 

[Skogsgurra]

I do not understand. You say that you have a wye to delta transformer. How, then, can you have a neutral? ("4 wire, 3+neutral"). Do you confuse Neutral and Ground?

But, if you actually have a neutral, the simple solution is to connect the 220 V loads between phase and neutral.

If you don't have a neutral, then the transformer is necessary. I see no other way. And that actually means that there is no other way. What did you have in mind?




Gunnar Englund

http://www.gke.org

 

[waross]

Hello skogsgurra
I'ts not often that I disagree with you, but... This sounds like a common US connection with Uncommon voltages. This sounds like 380 volt transformers connected Delta secondary with one transformer center tapped and the center tap used as the Ground/Neutral.
respectfully
Hello Zanana
It sounds like you have a Wye primary with a floating primary neutral.
The secondary sounds like a center tapped Delta.
If so, you will have the following voltages from the phases to neutral; 190V, 190V, and 220V.
If this assumption is correct you will have 220 volts to neutral on every third breaker in the panel. It's called the "Wild leg".
I am not familiar with these voltages, but the ratios are correct.
Further more, a condition of the Wye Delta distribution connection is the floating primary neutral. Distribution systems typically don't have the stability of transmission transformers and the Delta Bank will try to balance unbalanced voltages. This can result in transformer burnout or fuse blowing. Also, in the event of primary phase loss, the transformer with the missing primary phase will back feed into whatever loads are still connected to the lost primary phase. This can lead to transformer burnout and/or transformer primary fuse blowing depending on the relative sizes of the transformer and the connected load on the primary phase.
Solution; Run down the panel with your volt meter. Find the 220 volt "Wild" leg and connect your 220 volt loads from the wild leg to neutral/ground.
If this does not solve your problem, come back to us with the actual voltages that you can measure in the panel and we'll try again.
yours

 

[Skogsgurra]

Hi waross. I was thinking along those lines, too. But I decided that it could not be the case. For several reasons - the time-of-day of the OP is more European/African than "overseas" and also that a neutral, technically speaking, should be a neutral (i.e. where currents in a balanced system cancel, not a grounded center tap on a winding).

The third reason is that I couldn't see how to get 220 V from any delta wound secondary. A grounded center tap will only produce 380, 190 and 329 V in systems I know about. So, sorry, I do not follow you. How can it be done?

Gunnar Englund

http://www.gke.org

 

[waross]

Hi skogsgurra
you are absolutely right. I must have multiplyed the right ratio by the wrong voltage. Apologies.
respectfully.

 

[Skogsgurra]

OK, waross.

I have got to know you as a resourceful person. I thought you might have found a new (perhaps sensational?) solution.

KUTGW!

Gunnar Englund

http://www.gke.org

 

[CJCPE]

I interpret the described installation as a 380 volt delta source with a panel that requires a 4-wire, 380 volt wye source. As wired, the neutral terminal of the panel has nothing connected to it and is therefore "floating."

Two possible solutions:

1. Get a 380 volt wye secondary transformer to power the whole panel.

2. Disconnect the 220 volt circuitry inside the panel from the existing input power system and reconnect it to one or more 380:220 volt single phase transformers. This will result in a load imbalance on the 380 volt supply unless you use three single phase transformers to evenly distribute the load.

 

[waross]

Hello Zanana
Sorry if I misled you.
I think that CJCPE has your solution. Get a Wye Wye transformer bank or get a control transformer.
I think that you were misled when you were told that you couldn't get the voltages you need because the neutral was floating. You couldn't get the voltages you need because you have a delta secondary transformer bank that happens to have a floating neutral. It is strongly recommended that the center point of the tapped transformer be grounded for safety. The safety of both persons and equipment. It will no longer be floating, but you will still not have the voltages you need.
Yours

 

[waross]

Hello skogsgurra
Have you looked at the connection in thread238-148861 to derive three phase 120/208 volt power from two primary phases? That is a new one on me, but the vectors check out, and more importantly it's in service and working. It's not really an Open Wye (is it?) it's not really a Zig-Zag. Maybe a Wye-Zag.
Capacity wise it takes two 25 KVAs and a 50 KVA transformer to deliver 75 KVA of apparent power.
respectfully

 

[Zanana]

I checked again the wires ..all the motors are three phase.

its 5 wire white Neutral , Black , red , blue
(&green grounded)

I measure between white and black 200 volt

between white and red 229 volt

betwwen white and blue 230 volt

between red&Black or Red&Blue or Blue&Black 380 volt.

 

[RalphChristie]

Seems like a normal 3phase 4wire system at 380V. To obtain 220V you can use any one of the 3 phases and neutral. I am not familiar with the colour-code method you are using (we use Red, white and blue for the phases and black for the neutral) but looking back to your previous post and the way you mentioned the colours and the measurements, you can use either White-Black, White-Red or White-Blue to obtain 220V.

However, one measurement I am concerned about is the 200V between White and Black. It seems a little low and might be a bad/loose/high-resistance connection or even a internal fault in the transformer. You need to check it up.

Another thing:
You mentioned a floating neutral. According to your measured voltages the secondary side of your transformer is connected in star/wye. Can you confirm if your neutral is solidly grounded? If not, you have a ungrounded system. I am not familiar with the standards and codes you are using, but our local code states that:
Every electrical system rated at greater than 50V shall be connected to earth, between 50V and 1000V it shall be solidly grounded.
Anyway, the advantages of a grounded system outweigh the advantages of an ungrounded system by far. If you can, and if you have an ungrounded system, try to change it to a grounded system.

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[waross]

Hello Zanana
You mislead us somewhat stating that the system was a delta system. The primary may be delta but that would be a Delta-Wye, Not a Wye-Delta. In any event the primary connection is not important to the problem at hand.
Your measured voltages confirm that this is a Wye secondary system and RalphChristie is 100% correct in his advice. All of it.
yours

 

[CJCPE]

Zanana:

Are you describing the wires and voltages coming from your supply or the connection points at your panel? There seems to be some inconsistency. If you have white neutral, black, red and blue wires at the load and only black, red and blue coming from the source, you have some single phase items in the load dividing the voltage to give the voltages you measured with respect to a neutral point with no direct connection to the source. As single phase load items are switched on and off, the voltages with respect to the unconnected neutral will change drastically.

 

[LionelHutz]

I still think CJCPE is right.

I personally think those measured phase to neutral voltages are too inbalanced for a 4-wire panel. They seem more typical of a delta system when measured from phase to ground.

At any rate, to have both 380V and 220V available in the same panel you must have a Y secondary transformer feeding the panel. So, check the transformer itself and quit guessing. If your transformer is delta secondary then you will need a new transformer to supply 220V - either replacement Y secondary or an auxilary 380:220 control.

 

[davidbeach]

I agree that those voltages look like delta, not wye, voltages. This system needs a grounding transformer or the elimination of all line-neutral loads; preferably sooner rather than later as you are one wrong load combination (or one ground fault) away from catastrophic damage to your single phase loads. Separate transformer(s) to derive 220V from the 380V would be the quickest route to making this system much safer.

 

[waross]

The average neutral voltage is very close to 220 volts which will result in a phase voltage of 380 volts.
Down in the tropics primary voltages are not as stable as in the US and I am used to seeing this much unbalance on secondary voltages. The OP states that he has a neutral and a ground. If this statement is true, then the system will be a wye.
It needs to be established if the neutral connection is indeed floating, or if it is connected to the transformer. If the neutral is connected, those voltages describe a wye system. If the neutral is indeed floating, the system could be a wye or a delta system.
Zanana
If you have a three phase transformer the nameplate should indicate whether it is wye or delta secondary.
If you have three transformers, get back to us and we'll tell you how to identify the different connections.
yours