Y-Delta

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jbolen

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I have a transformer in Iraq 380 volt to 11,000 volt step-up transformer. This a Y-Delta transformer on the low side has XO persent. How is it treated. This is being feed by 1000 kva generator.

There is a huge disagreement over of if the xo from genrator is to be connected to XO on transfromer
 
jbolen said:
I have a transformer in Iraq 380 volt to 11,000 volt step-up transformer. This a Y-Delta transformer on the low side has XO persent. How is it treated. This is being feed by 1000 kva generator.

There is a huge disagreement over of if the xo from genrator is to be connected to XO on transfromer
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So you are saying that the primary of the transforer is a wye?
 
It would make little or no difference if the neutral was connected. The only current that would flow would be from the slight imbalance in the transformer windings. Without the connection to the generator, the X0 would just float to a voltage point that balances out the slight imbalance in the windings.
 
We normally do not ground the wye primary on a wye-delta bank on utility distribution systems (unless we are operating an open-wye open-delta bank).

Grounding the primary can turn the transformer into a grounding bank in the event of an unbalance on the primary side.
 
jbolen and I are on the same team in a middle eastern country and he has left out some details. The equipment is a step down transformer (delta to wye) used in reverse to push 380v uphill to 11K. It is fed from a 1meg generator that is wye wound and grounded at the center tap to a ground rod. The generator has overcurrent protection in the form of a breaker. The neutral conductors are not run between the XO's and the transformer is not grounded at XO. This voltage is then put on a local on-site overhead grid and sent several hundred yards to another simalar transformer that then steps it back down. This second transformer is grounded at Xo and has the appropriately sized neutral conductors to the load. The likelyhood of a fault on the overhead is mathimatically increased by the poor craftsmanship used in the installation. The norm here is to use metal power poles with metal cross arms and insulators from Turkey. How is the lack of conductors between the XOs and the lack of a ground at the "primary" transformer XO going to affect the alternator in the event of an 11K fault. How much benefit would these conductors give if they were installed. We know this will work as is but we want the maximum protection for this very expensive equipment.
 
Pierre C Belarge said:
Are you using this transformer in Reverse? It is possible that transformer was designed to be installed as a step down, not step up.


If so, make sure this can be installed as such..
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First, I would find out if the transformer can be installed in reverse, contact the manufacturer.

If so, I am sure they will also send you a wiring diagram. I do not see the need for a grounded conductor on the primary side, even if it is a Wye.
 
You need to ground the XO/neutral and hence then the grounded conductor at the generator. DO NOT connect the neutral to the XO, wye 380 VAC primary.
 
Pierre C Belarge said:
One separately derived system supplying another.

(do not forget to supply an EGC from the generator to the transformer)
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I mean in reality everything is separately derived, all electricity starts somewhere.

While the back feed is not the best situation IMO, I have installed quite a few generators that feed transformers to loads both step up and step down.
 
From what I have read about reverse wiring of transformers, it is not always permitted and sometimes just not a good idea.
Step up or step down does not necessarily mean reverse wiring. I would always consult the manufacturer, unless the instructions spell it out.
 
jbolen said:
I have a transformer in Iraq 380 volt to 11,000 volt step-up transformer. This a Y-Delta transformer on the low side has XO persent. How is it treated. This is being feed by 1000 kva generator.

There is a huge disagreement over of if the xo from genrator is to be connected to XO on transfromer
Click to expand...
If the generator neutral and the transformer are connected then you would avoid the problem of a floating neutral with potential unbalanced line to neutral voltages on the transformer LV side.
That would seem to me to be reason enough to make the connection. And I can see no reason not to.

Grounding is a different matter and something of a red herring here.
 
Currently the installation is in operation just as you have discribed.One of my main problems with all of this is the seriously unbalanced loads they have. Thier way of trim-out at the panel is to put all of the A/C on "A", the receptacles on "B" and the lighting on "C". Our main focus is to provide the installation that will protect the genset windings. We are about a year too late,so there are a lot of things we can not change at this point. thank you for your help.
 
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