Transformers

[Rahim84]

Hey guys,Bare with me I'm trying to understand this.So I have the three pictures from an animation of A step up Delta/wye configuration. But I'm still confused. Are the three phases electrically connected ? If so how isn't there a phase to phase fault..?

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[Fulthrotl]

CEMF provides the resistance.

the same way a motor winding doesn't dead short to ground.

yes, they all are connected to each other, but not primary to
secondary. primary to secondary is magnetically coupled, but
electrically insulated at every point besides the grounding point.

 

[Ingenieur]

In the case of a delta a coil is between any 2 lines
wye 2 cois between any 2 lines

both coils are sources that provide v/i transformation (power is essentially constant)

now if you jump between any 2 line then you have a ph-ph fault

 

[NewtonLaw]

Consider a single coil of wire first

Consider a single coil of wire first

Hey guys,Bare with me I'm trying to understand this.So I have the three pictures from an animation of A step up Delta/wye configuration. But I'm still confused. Are the three phases electrically connected ? If so how isn't there a phase to phase fault..?

View attachment 18060

Consider a single coil of wire first. The coil will have an inductance, "L", which at 60 Hz will represent an impedance of Xl = 2*pi*f*L for a pure inductor. I can place one phase on one end of the coil and a second phase to the opposite end of the coil. Current will flow through the coil according to I = V/Xl. This is not a short circuit current.

Next consider three coils connected in series end to end with the end of the last coil connected to the beginning of the first coil. This is the same configuration for the Delta side of a transformer. Now with you three coils, attach one phase to the junction between coils #1 & #2, a second phase to the junction between coils #2 and #3 and the last phase to the junction between coils #3 and #1. Again current will flow according to the voltage and impedance of the phases and the inductance of the coils. Not a short circuit.

Next have all the coils wrapped around an iron core (we'll call these the primary coils). The impedance will increase as "L" has increased. Now less current flows and still not a short circuit. Now place a second set of coils (we'll call them secondary coils) wrapped around the iron core. The magnetic flux created by the primary coils will induce a back voltage and back flux that will act to increase the input impedance seen by the primary phases and thus reduce the input current to the current necessary to energized the "transformer" and supply losses like eddy currents and hysteresis losses.

Last the secondary coils may be connected as Wye or Delta as needed.

Hope this helps.

 

[Rahim84]

Thank you all, very helpful. I have to study more basic theory to truly grasp it better.


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[ActionDave]

Thank you all, very helpful. I have to study more basic theory to truly grasp it better.


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You don't need to study more basic theory unless you want to learn all that maths stuff some of the guys posted. To get started all you really need to do is get your head around the idea that there is no connection between the primary and secondary windings, they are totally separate. It's that AC magnetic induction rising and collapsing sixty times a second that induces the charge from one winding to the other.

 

[Rahim84]

You don't need to study more basic theory unless you want to learn all that maths stuff some of the guys posted. To get started all you really need to do is get your head around the idea that there is no connection between the primary and secondary windings, they are totally separate. It's that AC magnetic induction rising and collapsing sixty times a second that induces the charge from one winding to the other.

Yea I need a simpler answer like this, but I get that part. It's the primary side I'm trying to understand, what allows the primary side to be electrically connected with three separate phases


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[Smart $]

Yea I need a simpler answer like this, but I get that part. It's the primary side I'm trying to understand, what allows the primary side to be electrically connected with three separate phases.

You have to back up in your learning... or we have to review your understanding of concepts which should have come earlier in your development.

Do you understand how current passing in one direction through a straight wire creates a magnetic field around the wire? What are the characteristics of that magnetic field? Is it polar? Is it stationary or is it moving? What happens to the magnetic field if the current stops abruptly? What happens with the magnetic field if the wire is coiled?

 

[ActionDave]

Yea I need a simpler answer like this, but I get that part. It's the primary side I'm trying to understand, what allows the primary side to be electrically connected with three separate phases


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It's the windings. You can take a five hundred foot roll of 12AWG THHN and hook one end of the spool up to a hot, hook the other end of the spool up to a neutral, flip the switch and it won't trip a breaker. Look at the lower left corner of your pic of the delta primary. Picture each one of those windings as a roll of wire.

 

[ggunn]

You don't need to study more basic theory unless you want to learn all that maths stuff some of the guys posted. To get started all you really need to do is get your head around the idea that there is no connection between the primary and secondary windings, they are totally separate.

Unless it's an autotransformer, of course.

 

[ActionDave]

Unless it's an autotransformer, of course.

Well get into that when the op is ready.

 

[Rahim84]

It's this part I'm struggling with, so you can add three separate phases to these spots. Which are electrically connected and not have any issues? (Obviously cuz that's how it's done)


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[Ingenieur]

It's this part I'm struggling with, so you can add three separate phases to these spots. Which are electrically connected and not have any issues? (Obviously cuz that's how it's done)


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yes
each is seperated by a coil
the coil has voltage across it
when a load is connected current flows

let each coil have 100 v
and you connect 10 Ohm across it
i = 100/10 = 10 A
100 v across the coil and -100 across the load
since v = ir, if the coil has 100 volt and 10 A it must have r = 10 Ohm
no short circuit
coil r (actually z or impedance) is a result of coil inductance, as i increases r decreases

now if load is 1 Ohm
i = 100 A
and coil r = 1 Ohm

now if load is 0.1 Ohm
i = 1000 A
and coil r = 0.1 Ohm

if load is 0 Ohm
i goes to infinity (actually limited by winding r about 0.01 Ohm for example)
this is a short circuit
detrrmined by the load not the source or supply (coil)
and its r is dtermined by i flow which is determined by the load

 

[mivey]

It's this part I'm struggling with, so you can add three separate phases to these spots. Which are electrically connected and not have any issues? (Obviously cuz that's how it's done)


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Connected through an impedance. Follow the path between Y, R, B: it goes through a coil, not just a straight wire.

Kinda like connecting Y and B across a large resistor: nothing bad happens because the resistance limits the current. The coil is a circuit component and you will have something between Y and B and R other than just a wire with very little resistance. The energized coils will limit the current between Y and B and R.

 

[ggunn]

It's this part I'm struggling with, so you can add three separate phases to these spots. Which are electrically connected and not have any issues? (Obviously cuz that's how it's done)


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Yes, it's because of the inductance in the coils. It provides an impedance to current flow, which is sort of a time dependent resistant response to AC voltage. If you were to apply 480V DC with no current limit to the coils, they would likely burn up.

 

[ActionDave]

It's this part I'm struggling with, so you can add three separate phases to these spots. Which are electrically connected and not have any issues? (Obviously cuz that's how it's done)


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This is your answer...

Connected through an impedance. Follow the path between Y, R, B: it goes through a coil, not just a straight wire.

Kinda like connecting Y and B across a large resistor: nothing bad happens because the resistance limits the current. The coil is a circuit component and you will have something between Y and B and R other than just a wire with very little resistance. The energized coils will limit the current between Y and B and R.

 

[Rahim84]

Okay I feel better about it now. Thanks you all


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[Electric-Light]

The phase relationship.

If you have a single phase transformer with two 120v to allow same kVA in either 120v or 240v, you connect it in series for 240v, in parallel for 120v, but if you parallel it backwards, they are 180 degrees out of phase and it will short out.