Connecting a neutral to a 3-Phase Wye Load

[rattus]

OK thanks alot for the help guys it has made it much clearer what is going on, and I also see there is more than one way to skin this cat.

I wanted to apply this application to real system components to see where it applies. For example:

If I have a wye secondary of a transormer that feeds several single phase loads (L-L) and has no neutral connected then will the neutral of the secondary float? I would think not in this case because all loads are L-L and would be the same as if I did have a neutral on the wye that nothing would flow through the neutral because all loads are L-L?

It seems like we will only have the floating neutral condition talked about in this thread in three phase "loads" and not sources. These loads could be an unbalanced heater arrangement as mentioned, or a (3) phase motor in wye that had three unequal impedances?

The neutral node of the wye secondary will "float" if not connected to ground, but the phase voltages being measured relative to the common neutral will be unaffected. Likewise, the L-L voltages and load currents will be unaffected.

An open neutral on an unbalanced wye load will cause the neutral voltage to be something other than zero, but this voltage will be relatively stable (if the secondary is grounded) because it is created by IR drops in the load impedances. Doesn't really float.

 

[mull982]

The neutral node of the wye secondary will "float" if not connected to ground, but the phase voltages being measured relative to the common neutral will be unaffected. Likewise, the L-L voltages and load currents will be unaffected.

When your refering to the neutral node floating here, it is because of capacitance coupling to ground, not anything to do with load unbalance as we have been disucssing. Is this correct?

Even if there was a neutral connected there would be no current flowing through the neutral since all loads are L-L. Is this right?


An open neutral on an unbalanced wye load will cause the neutral voltage to be something other than zero, but this voltage will be relatively stable (if the secondary is grounded) because it is created by IR drops in the load impedances. Doesn't really float.[/QUOTE]

So it sounds like this only applies to 3-phase "wye loads only" and does not apply to single phase loads connected on a wye system. Is this right?

I think I almost have it. But then I'm sure something else will pop up that makes it all confusing again.

 

[Smart $]

So it sounds like this only applies to 3-phase "wye loads only" and does not apply to single phase loads connected on a wye system. Is this right?

It also applies to 1? L-N loads on a 3? wye system when the neutral conduction path is shorted open or or has high impedance due to a faulty connection.

L-L loads are not affected by a neutral or lack thereof.