High Leg Delta

[SG-1]

There have been many discussions on this topic. I think one fell into my lap tonight. :jawdrop: Thank goodness it missed my foot !!
I am wondering how the transformer secondary is marked, since I have never seen or touched one before.

X1,X2,X3,GND ?? As on the NP below.
Is there any question that a grounded conductor could be attached to terminal GND to serve 115 volt loads ?

 

[broadgage]

Provided that the grounded terminal is indeed properly grounded in a code compliant manner, then yes 120 volt loads could be connected between the grounded terminal and the appriopiate phase terminals.
Take care that no such loads are accidently connected between the grounded terminal and the high phase.
Take care that the winding with the center tap is not overloaded, as could readily occur if the 120 volt loads are substantial.

 

[qcroanoke]

Provided that the grounded terminal is indeed properly grounded in a code compliant manner, then yes 120 volt loads could be connected between the grounded terminal and the appriopiate phase terminals.
Take care that no such loads are accidently connected between the grounded terminal and the high phase.
Take care that the winding with the center tap is not overloaded, as could readily occur if the 120 volt loads are substantial.

Shouldn't there be an X-O connection shown for where the grounded conductor connects on the secondary of the xfmr?
Secondary voltage is 230. Not 120/230.

 

[ggunn]

There have been many discussions on this topic. I think one fell into my lap tonight. :jawdrop: Thank goodness it missed my foot !!

If it landed in your lap, I wouldn't think it would be your foot you'd be worried about.

 

[SG-1]

Shouldn't there be an X-O connection shown for where the grounded conductor connects on the secondary of the xfmr?
Secondary voltage is 230. Not 120/230.

I was expecting an X0 terminal too. Now I am wondering if the presence of an X0 terminal on the secondary side always indicates a WYE secondary.

 

[SG-1]

If it landed in your lap, I wouldn't think it would be your foot you'd be worried about.

I could not get the umbrella opened in time. :blink:

 

[Smart $]

Shouldn't there be an X-O connection shown for where the grounded conductor connects on the secondary of the xfmr?
Secondary voltage is 230. Not 120/230.

I was expecting an X0 terminal too. Now I am wondering if the presence of an X0 terminal on the secondary side always indicates a WYE secondary.

I wouldn't go to the degree of saying "always" :huh:, but in my expoerience, practically all that had one terminal marked X0 were wye secondaries.

FWIW, I've seen delta center tap terminals marked X4.

 

[augie47]

I wouldn't go to the degree of saying "always" :huh:, but in my expoerience, practically all that had one terminal marked X0 were wye secondaries.

FWIW, I've seen delta center tap terminals marked X4.

Same here. But that nameplate looks like it might be older than I am (strange, if that were the case one would expect hieroglyphics )

 

[Smart $]

...it might be older than I am (strange, if that were the case one would expect hieroglyphics )

Same here lol::lol::lol

 

[SG-1]

Same here. But that nameplate looks like it might be older than I am (strange, if that were the case one would expect hieroglyphics )

The NP does look old, but the CPT is brand spanking new being prepared for it's end user.

 

[SG-1]

Provided that the grounded terminal is indeed properly grounded in a code compliant manner, then yes 120 volt loads could be connected between the grounded terminal and the appriopiate phase terminals.
Take care that no such loads are accidently connected between the grounded terminal and the high phase.
Take care that the winding with the center tap is not overloaded, as could readily occur if the 120 volt loads are substantial.

Thank you for confirming my suspicions. The GND terminal is connected to a nice ground bus. We are wiring the four terminals out for our customers use.

 

[SG-1]

I wouldn't go to the degree of saying "always" :huh:, but in my expoerience, practically all that had one terminal marked X0 were wye secondaries.

FWIW, I've seen delta center tap terminals marked X4.

Thanks Smart, I always appreciate your input.

 

[SG-1]

Same here. But that nameplate looks like it might be older than I am (strange, if that were the case one would expect hieroglyphics )

Augie, one customer returned a network protector that was built in the late 1890s, maybe by George Westinghouse himself. They complained it had stopped working. That one had a nameplate older than you. We just don't build them like that any more. :happysad:

 

[Hv&Lv]

There have been many discussions on this topic. I think one fell into my lap tonight. :jawdrop: Thank goodness it missed my foot !!
I am wondering how the transformer secondary is marked, since I have never seen or touched one before.

X1,X2,X3,GND ?? As on the NP below.
Is there any question that a grounded conductor could be attached to terminal GND to serve 115 volt loads ?




View attachment 7097

240 phase to phase, 120V X1 to G, 120V X3 to G, 208 X2 to G
not any ungrounded conductor, just the X1 and or X3. Both together will be 240.

 

[kwired]

Thank you for confirming my suspicions. The GND terminal is connected to a nice ground bus. We are wiring the four terminals out for our customers use.

If that nice ground bus is bonded to the transformer enclosure then that is your system bonding jumper you will need separate neutral and equipment grounding conductors leaving that bus if you are going to supply loads that require a neutral.

 

[hurk27]

I could not get the umbrella opened in time. :blink:

I dont think an umbrella would help with a 600# transformer:blink:

 

[SG-1]

If that nice ground bus is bonded to the transformer enclosure then that is your system bonding jumper you will need separate neutral and equipment grounding conductors leaving that bus if you are going to supply loads that require a neutral.

This CPT has no enclosure, except the rear compartment of the arc-resistant switchgear it is sitting in.
The frame is bonded to the ground bus.
The GND terminal is bonded to the ground bus.
Four conductors X1,X2,X3,GND are brought to a terminal block in the front of the gear for customer use via a 3 pole breaker.

We do not actually know if the loads require a neutral or not. Building per the approval drawings.

 

[SG-1]

I dont think an umbrella would help with a 600# transformer:blink:

I know it helps because the coyote survives everything that falls on him. Thats his PPE :happyyes:

 

[SG-1]

240 phase to phase, 120V X1 to G, 120V X3 to G, 208 X2 to G
not any ungrounded conductor, just the X1 and or X3. Both together will be 240.

Re-calculating for 230V secondary.

115V X1 to G, 115V X3 to G, 199V X2 to G.
230V between X1-X2 & X2-X3 & X3-X1.

 

[Phil Corso]

I believe the xfmr is improperly taggd.

'0' is reserved for the neutal-connection where by definition the "neutral conductor" is the one that usually is grounded and has equipotential (excluding phase displacement) measurements from every other conductor. Therefore, although the center-tap of one winding with regard to the two terminals of the same winding of a "red", "high", "bitch", etc-leg delta connection, is technically correct... there is no equipotentil measusurement from all other conductors!

The term "neutral" is used by convention, simply for the lack of a better term. When used in single-phase 3-wire circuits, the term "neutral conductor" is correct.

In 3-phase, 3-wire circuits, there is a "neutral point" that meets the definition above for both the conventional wye and delta-derived systems. In the former, the neutral point is a "physical" one. In the latter, there is no "physical" neutral point, but there is a "virtual' one, namely the centriod of the triangle.

For 4-wire, wye-connected circuits, the "neutral point" is usually "grounded", hence its distribution conductor becomes the "neutral conductor". But, for 4-wire delta-connected circuits like the "grounded-corner" and "mid-point grounded" (both unusual in European practice) the definition is not met. However, by USA convention the "grounded conductor" is labeled the "neutral conductor"! Phew!

Regards, Phil Corso,