Transformer windings and ungrounded conductors

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TFW

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Okay I have a question... I am new to this forum and AM taking my masters electrical license test in March. I am going throughh Mike Holtz master exam prep course ( which is amazing) and in the section about transformers.... My question is.... why and or how are all the wires connected in the coil setup of the primary and secondary... Would that not be a dead short like it would be at the service, feeder or branch circuits wires? I know it is obviously not a dead short because that is the way the systems work but I don't know how that works or why that works.... I know that is the path for the electrons to get back to their source but do not understand the concept.
 
I need a picture, in order to understand your question. I do not have a copy of the Mike Holt book to which you refer. Can you sketch something up and post it?

Welcome to the forum.
 
TFW said:
Okay I have a question... I am new to this forum and AM taking my masters electrical license test in March. I am going throughh Mike Holtz master exam prep course ( which is amazing) and in the section about transformers.... My question is.... why and or how are all the wires connected in the coil setup of the primary and secondary... Would that not be a dead short like it would be at the service, feeder or branch circuits wires? I know it is obviously not a dead short because that is the way the systems work but I don't know how that works or why that works.... I know that is the path for the electrons to get back to their source but do not understand the concept.
Click to expand...
Welcome to the forum. This is a great place to learn.

I'm not understanding your question either. Are you asking how does a transformer work?
 
My question is, at the transformers secondary windings, lets say its a wye, you have the 3 phase coils separated 120 degrees coming together in the middle and your ground and grounded conductor (neutral) terminate there too.....how is this possible? If I was to do this on premises wiring -- ungrounded to grounded conductor connection, there would be a dead short or a line to neutral short...is it because of the resistance or impedance of the windings wires? I'm just trying to understand exactly how that portion works. I understand the rest of the operation of transformers, thanks to Mike Holtz.


Id post a pic but any pic of a secondary Wye's coil setup should suffice. I hope I've explained myself a little better this time and I may have already answered my own question with the resistance statement. IDK
 
TFW said:
. If I was to do this on premises wiring -- ungrounded to grounded conductor connection, there would be a dead short or a line to neutral short...is it because of the resistance or impedance of the windings wires?
Click to expand...

Like the others, I don't know that I fully understand your question. But I'll take a shot at an answer anyway. You are looking at the transformer winding as a dead short. Understood. It's just a bunch of copper wire wound many times around an iron core after all. The answer lies in something you touched on, which is impedance. A transformer winding will typically have a relatively low - very low - resistance. But it will have significant reactance. And impedance is the vector sum of resistance and reactance. When an AC voltage is impressed across the primary winding of a transformer, it's the impedance which limits the current flow. There more of course, but I'll stop here. Apologies if I've confused the issue or answered the wrong question. If so, I'm sure someone else will step up.
 
Action dave... Thank you for the article... That helped me understand a little bit more... I appreciate all the replies and do you have a little bit more of an understanding of it than I did before. Thanks.
 
Think of just one phase....if you take an energized 240/120v transformer the 240 winding magnetically energizes the secondary winding. Hook a 120v lamp across across the secondary and the lamp lights because current flows through the filament. Disconnect the lamp and no current flows because even though the 120V is still there, it has no circuit. If grounding adds confusion, it has nothing to do with whether or not it's grounded on one end. Same for three phase. Grounding the center (neutral) of the Wye does not change the current path. Still Line to Neutral. But...also ground the other end of the winding, and POW....dead short and mucho current. Some installations don't ground the neutral. Navy ships are a good example...ungrounded neutrals. Grounding has mostly to do with safety and ground fault tripping. Hope I didn't offend you, but other less educated folks read these threads, too.
 
It seems like the two points to understand are:

1. The transformer coil does have resistance as described above. When a voltage is applied current flow is impeded by magnetizing the core.

2. The ground should only be connected at one point. Think of the ground connection as a reference point. It is a reference point to what humans are touching. It is considered to be a point which would have a potential of 0 volts to ground. It could be at the neutral of a wye where all phases meet. I could be at a corner or center of a delta. It could be at the center or end of a single phase. It could be just about anywhere. The important thing is that it is only in one place.

What could happen if we did not make a connection to this theoretical 0 volt reference point?
 
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