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# Transformer neutral connection

1. Junior Member
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Jul 2019
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## Transformer neutral connection

What will happen if one LT phase winding having finishing point as neutral connected to the other two phases having starting point as neutrals?

2. Originally Posted by sahoojoge
What will happen if one LT phase winding having finishing point as neutral connected to the other two phases having starting point as neutrals?
I'm not sure what you are asking?
Sounds like you have a three phase transformer with wye secondary which then has two phases shorted to neutral. Next question would be is neutral grounded? Either way sounds like you have two phases shorted to neutral removing the impedance and potentially causing an arc flash waiting to happen.

Otherwise you just described a Wye connection on a transformer, where 'A' phase wire lands and across a winding has neutral landed at the same point two windings are connected and at the other end is 'B' and 'C' phase.

3. Originally Posted by Kalbi_Rob
I'm not sure what you are asking?
Sounds like you have a three phase transformer with wye secondary which then has two phases shorted to neutral. Next question would be is neutral grounded? Either way sounds like you have two phases shorted to neutral removing the impedance and potentially causing an arc flash waiting to happen.

Otherwise you just described a Wye connection on a transformer, where 'A' phase wire lands and across a winding has neutral landed at the same point two windings are connected and at the other end is 'B' and 'C' phase.

When I read that question the first thing that comes to mind is a three phase bank with one transformer reversed polarity. We need more clarification from OP.

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## lt

Originally Posted by sahoojoge
What will happen if one LT phase winding having finishing point as neutral connected to the other two phases having starting point as neutrals?
I believe you are basically shorting the transformer out. I have never heard of wiring a transformer this way

5. Originally Posted by sahoojoge
What will happen if one LT phase winding having finishing point as neutral connected to the other two phases having starting point as neutrals?
If I am not mistaken, you are trying to ask:
What will happen if the polarity of two of the coils inside a 3 phase Y connected transformer were reversed?...

First of all, it would be pretty hard to mix up the intended starts and finishes of each winding given the connection is most commonly by a bus bar at either the top or bottom of the coils...

Simply put, it would likely cause voltage issues & circulating currents to flow (Seen as a higher No Load Loss result), assuming all windings share the same core. While a transformer is an AC device, the Induced Flux in the core changes with the direction of the current flow (Left hand rule). The transformer flux linkage of one coil that has been connected in the opposite direction and will be subtractive.

In addition, if the transformer is subjected to fault currents it can cause mechanical issues (Depending on the topology of the other winding(s) on that core leg). Simply put, by design a transformers inner and outer coils should be magnetically aligned to reduce or ideally mitigate Axial forces (typically resulting in axial displacement of the windings or 'telescoping') This is because the inner and outer windings on any given core leg are most commonly wound in opposite directions so that under normal conditions, the net magnetic flux results only in a radial force (Inner winding typically compressive, outer usually expansive).

Hope that helps.

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