Wye Primary Transformer Neutral 6

[nightfox1925]

I have a 750KVA dry type transformer to be installed in a system. Primary winding is 480Volts Wye and Secondary winding is 208/120v Wye. I understand that the secondary neutral is required to be bonded to ground in order to prevent floating neutral in case there are 120v 1phase loads .

However my question is;

In case the power source is coming from 480 volts 3phase 3 wire delta, Is it required or necessary to bond the transformer primary neutral to ground?

In case the power source is coming from a 480 volts 3phase 4wire Wye, is it required to connect the neutral of the power source to the neutral of the drry type transformer primary?

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[davidbeach]

Bill, it is a wye-wye transformer. Think 480Y-208Y.

 

[waross]

Yes David, I was thinking 480/277Y:208/120Y.
My second line:
You have shown a 480/277 volt primary and a 120/240 volt secondary with a phase to phase load on the secondary.
Should read:
You have shown a 480/277 volt primary and a 208/120 volt secondary with a phase to phase load on the secondary.
I am visualizing an equilateral triangle A, B, C, to represent the delta supply.
Inside the delta I visualize a wye to represent the 277 volt windings of the 480 volt wye primary.
This wye will be distorted with unequal loads. With a singlephase load, the internal wye will become a "T"
With the single phase load from A to C, two of the internal vectors will form a straight line from A to C, with the third vector from the center point to "B". The straight line vectors represent the phase angles of the two loaded windings. The magnitude of the vectors represent 240 volts applied to each 277 volt winding.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jghrist]

Bill,

I think you are visualizing it correctly. A and C windings will have 240 volts. The B winding will have 415.7 volts.

 

[waross]

Thanks jghrist and David.
Respectflly

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

And that is where I was trying to go when I wandered off into the weeds talking about a "simpler" example with a load connected to only one phase. Thanks guys for pulling it back out of the weeds.