Wye Transformer - Secondary

[DMG_1]

Hi All.

I am making the transition from the low voltage world to the medium voltage world. I have two situations where I have a Utility Transformer as the source, Delta (Primary) - Wye (Secondary). In the first case we are feeding a 4160 Switchgear which inturn feeds multiple outdoor substations. In the second case I am feeding multiple indoor substations. In the low voltage world I would always pull a neutral because I was feeding power / lighting panels. In both of the cases above I am being told that we will not be pulling a neutral. Can anyone tell me as to when a Neutral would be required from a Wye Secondary and advantages / disadvantages as to pulling one?

Thanks.

 

[bob]

Are you talking about a neutral with the 4 kv cable?

 

[DMG_1]

Yes

 

[bob]

If the primary to the transformer is delta connected there is no need for a neutral. You will need to install an EGC for the transformer.

 

[templdl]

Bob is right on. It is not uncommon for some to think that should you have a wye secondary the primary of a down stream transformer must be a wye also which is not correct, I have found the wye primaries are more apt to be used by utilities.

 

[jghrist]

Hi All.

I am making the transition from the low voltage world to the medium voltage world. I have two situations where I have a Utility Transformer as the source, Delta (Primary) - Wye (Secondary). In the first case we are feeding a 4160 Switchgear which inturn feeds multiple outdoor substations. In the second case I am feeding multiple indoor substations. In the low voltage world I would always pull a neutral because I was feeding power / lighting panels. In both of the cases above I am being told that we will not be pulling a neutral. Can anyone tell me as to when a Neutral would be required from a Wye Secondary and advantages / disadvantages as to pulling one?

Look at it this way. If all of the loads are connected phase-to-phase or to a delta winding (that has no neutral), then if you pulled a neutral, nothing would be connected to it. If that's the case, it has no purpose. You need an EGC in case there is a phase-to-ground fault to carry the fault current back to the source.

 

[Shoe]

Yep, only pull a neutral if you need one. To translate to your low-voltage experience, think of it as a 480V, 3-wire distribution to a motor control center that might feed all 3-phase loads and a few delta-wye transformers. You wouldn't be inclined to pull a neutral in that case either.