Master Electrician

[mattczarnocki1234@gmail.c]

I'm working on a 400KVA transformer primary side star 3phase 4 wire 480/277 volts secondary side star 3phase 4 wire 240/139.2 volts. Industrial application Lighting and machinery. Question, Is this transformer the right application? How do you ground this transformer? I'm confused because the primary side has a neutral.

 

[augie47]

Odd voltage but same principles. What voltage is the lighting ?
Ignore the neutral on the 480 side and connect only the 3 phase 480.
On the secondary side you can ground the neutral and follow the rules in 250.30.

 

[JFletcher]

Augie, with these voltages, why have a neutral on the secondary side? Is there any standard single phase equipment that runs on 135-140V? 240V single phase loads would run L-L, and 230V 3ph motors on all three. Would there be a step-down transformer to get 120VAC out of this system?

 

[fmtjfw]

Read 250.20 and 250.21

 

[infinity]

I'm working on a 400KVA transformer primary side star 3phase 4 wire 480/277 volts secondary side star 3phase 4 wire 240/139.2 volts. Industrial application Lighting and machinery. Question, Is this transformer the right application? How do you ground this transformer? I'm confused because the primary side has a neutral.

Nothing more than a WYE/WYE transformer. Just ignore the X0 connection on the primary. Since the secondary has an X0 it must be grounded just like any other WYE secondary.

 

[GoldDigger]

If the OP chose a wye delta transformer instead because only 240V loads would be used, then he would have to deal with corner grounding instead.
If only 240V loads are needed, then a 416Y/240 secondary (non standard) would allow use of single pole breakers (not slash rated). The proposed 240Y/139 would not allow use of 120/240 rated breakers either.

 

[electrofelon]

Augie, with these voltages, why have a neutral on the secondary side? Is there any standard single phase equipment that runs on 135-140V? 240V single phase loads would run L-L, and 230V 3ph motors on all three. Would there be a step-down transformer to get 120VAC out of this system?

I agree a neutral with this configuration would pretty much serve no purpose, however we have to be clear about whether we are talking about using/running the neutral to distribution equipment vs just grounding the wye point and not distributing it.

 

[don_resqcapt19]

The only place I have seen that voltage used is as a drive isolation transformer.

 

[iceworm]

The only place I have seen that voltage used is as a drive isolation transformer.

That's the only application I've seen. The mfg specs 240V, 3ph and does not want un-grounded or corner grounded.

But I don't know why the 480Y primary. I've only seen about two of these, both were 480D/240Y.

Matt - If you are not time constrained, call and ask, "Why Wye?" Maybe they ordered/shipped the wrong xfm.

ice

 

[don_resqcapt19]

That's the only application I've seen. The mfg specs 240V, 3ph and does not want un-grounded or corner grounded.

But I don't know why the 480Y primary. I've only seen about two of these, both were 480D/240Y.

Matt - If you are not time constrained, call and ask, "Why Wye?" Maybe they ordered/shipped the wrong xfm.

ice

Yes the ones I have seen were also delta/wye.