is this supposed to be?

[synchro]

I'm not sure which transformer you are referring to that is similar to a T connection. The 12KV/480V is a T-T transformer with a tap X₀ on the teaser winding of the secondary for a neutral.
The transformer in your first post on this thread can be viewed as a wye-wye but with one of the three output phases created by two secondary windings in an open delta, and with one of the two "open" terminals of the delta tied to neutral.

 

[Hv&Lv]

Is this similar to a T connection? Or the same thing?

I’m not so sure this isn’t supposed to be posted in another thread you have here?
the one with the Scott t maybe...

 

[mbrooke]

I’m not so sure this isn’t supposed to be posted in another thread you have here?
the one with the Scott t maybe...

Nope, this one. I'm curious if this derives 3 phase the same way the two pot bank does. Actually, what is the two pot bank called or drawn out vector-ally?

 

[Hv&Lv]

1

 

[LarryFine]

It’s not the prettiest drawing, but here...
crap... I left the ground off at the center... imagine a ground at the center point.

Well done! :thumbsup:

 

[Hv&Lv]

Well done! :thumbsup:

Thanks, you may have to zoom in to see the negative signs on the left.

 

[mbrooke]

It’s not the prettiest drawing, but here...
crap... I left the ground off at the center... imagine a ground at the center point.

Errr, still kind of confused :dunce:

 

[LarryFine]

Errr, still kind of confused :dunce:

The bodies of the arrows represent transformer windings; the tips of the arrows represent the transformer output terminals.

Added: I mean the three arrow tips at #3, #1, and - #3. Ignore - #1, and pretend that the blue dotted line is a real winding.

Note that the tips of the arrows form a triangle around the center point, and represent the three phases and neutral of a wye.

Added: Abracadabra! Now you have a functional wye three phase supply from two transformers.

 

[mbrooke]

The bodies of the arrows represent transformer windings; the tips of the arrows represent the transformer output terminals.

Added: I mean the three arrow tips at #3, #1, and - #3. I ignore - #1, and pretend that the blue dotted line is a real winding.

Note that the tips of the arrows form a triangle around the center point, and represent the three phases and neutral of a wye.

Added: Abracadabra! Now you have a functional wye three phase supply from two transformers.

Dumb it down a bit for me

 

[LarryFine]

Dumb it down a bit for me

Didn't I? :angel: rotflmao

 

[mbrooke]

Didn't I? :angel: rotflmao

That was dumbed down :huh: I'm not as bright as you

 

[synchro]

1

 

[Hv&Lv]

B

 

[LarryFine]

That was dumbed down :huh: I'm not as bright as you

Okay, presuming you're being serious, let me try again. Look at this image:

Now, let's say the red arrow is made up of a pair of 120v transformer secondaries wired in series as a typical center-tapped 120/240v secondary. Let's also say the two green arrows are another pair of 120v secondaries that are physically wired as shown in the drawing, one end of one connected to the center tap, one end of the other one connected at arrowhead - #1.

The arrowhead end of arrow - #3 will put out a voltage that is at the same voltage relative to the neutral point (the center of the green arrow where the tail of arrow #3 meets it), as arrowheads #1 and #3 will, or 120v. The third arrowhead, - #3, will also be at 120v relative to the neutral point, making it behave as if there was a 120v secondary along the dotted blue line.

What's happening is being able to mimic having three 120v secondaries without having three transformers, not unlike how an open delta system does. Arrowheads #1, #3, and - #3 will put out three phases of power, each with 120v to the neutral point, as if there were three secondaries connected as a wye. If you can grasp the open-delta concept, this isn't too far away.

 

[mbrooke]

Let's give it a try, even though it will duplicate what Larry said to a great extent:
The phasors in Hv&Lv's diagram below represent the voltages across each secondary winding on the two transformers. The origin and the tip of each phasor corresponds to the terminals at the end of each secondary winding. The red phasors are from one transformer, and the green ones from the other. Note that each transformer can only produce a phasor in one direction in the complex plane (or its 180 degree opposite just by reversing the winding polarity). The transformers are operating 120 degress from eachother but we need a third phase. Where the origin (i.e., starting point) of the phasor is located is determined by where the corresponding end of the winding is connected in the circuit.

Phasors and corresponding secondary windings:

second transformer
X₂ connected to N
red phasor #1: X₂ to X₁
red phasor -#1: X₂ to X₃ (reverse polarity of #1)

first transformer
X₂ connected to N
green phasor #3: X₂ to X₁
green phasor -#3: X₃ to X₄ (reverse polarity of #3)

So origin of red phasor -#1 is the neutral
The origin of green phasor -#3 is the end of red phasor -#1 because of the connection between the X3's of each transformer. Basically, green phasor -#3 is added to red -#1 because its corresponding winding is in series with that of -#1. The sum of these two phasors creates a new phasor referenced to N which is blue #2 on HV&Lv's diagram. Phasors -#1 and -#3 form an open delta, where one end of the open delta is connected to neutral (at the origin of -#1) and the other end creates the new blue #2 phasor, which goes from neutral to the end of the -#3 phasor.

Green phasor #3 and red phasor #1 are of course the two phases of the wye output coming directly from each transformer. Therefore blue #2 completes all three output phases of the wye.

I hope that was wordy enough

Got up, let me digest this and I will get back to everyone

 

[kwired]

Is this similar to a T connection? Or the same thing?

HV: 1200T

LV: 480T/277

do not claim to be an expert on the T configuration, but think maybe is a T connection.

 

[mbrooke]

HV: 1200T

LV: 480T/277

do not claim to be an expert on the T configuration, but think maybe is a T connection.

But wouldn't the original 2 pig bank also classify as a T?

I only know of T, Y, Delta, and open delta in 3 phase.

 

[mbrooke]

Let's give it a try, even though it will duplicate what Larry said to a great extent:
The phasors in Hv&Lv's diagram below represent the voltages across each secondary winding on the two transformers. The origin and the tip of each phasor corresponds to the terminals at the end of each secondary winding. The red phasors are from one transformer, and the green ones from the other. Note that each transformer can only produce a phasor in one direction in the complex plane (or its 180 degree opposite just by reversing the winding polarity). The transformers are operating 120 degress from eachother but we need a third phase. Where the origin (i.e., starting point) of the phasor is located is determined by where the corresponding end of the winding is connected in the circuit.

Phasors and corresponding secondary windings:

second transformer
X₂ connected to N
red phasor #1: X₂ to X₁
red phasor -#1: X₂ to X₃ (reverse polarity of #1)

first transformer
X₂ connected to N
green phasor #3: X₂ to X₁
green phasor -#3: X₃ to X₄ (reverse polarity of #3)

So origin of red phasor -#1 is the neutral
The origin of green phasor -#3 is the end of red phasor -#1 because of the connection between the X3's of each transformer. Basically, green phasor -#3 is added to red -#1 because its corresponding winding is in series with that of -#1. The sum of these two phasors creates a new phasor referenced to N which is blue #2 on HV&Lv's diagram. Phasors -#1 and -#3 form an open delta, where one end of the open delta is connected to neutral (at the origin of -#1) and the other end creates the new blue #2 phasor, which goes from neutral to the end of the -#3 phasor.

Green phasor #3 and red phasor #1 are of course the two phases of the wye output coming directly from each transformer. Therefore blue #2 completes all three output phases of the wye.

I hope that was wordy enough

Kind of getting it with the open delta reference. Give me more time...

 

[Hv&Lv]

HV: 1200T

LV: 480T/277

do not claim to be an expert on the T configuration, but think maybe is a T connection.

It is. It’s a back to back T.
notice the secondary diagram. With the neutral connected up on the coil that high the resulting V-G voltages are the same.
think of an open delta missing one coil... think of this one as missing two..
the voltages of X1, X2, and X3 will be the same also.

 

[mbrooke]

Can someone post the vector math for this connection? Very creative, 25+ years of studying the theory and I never knew you could do this. Wow! Go Engineers!