# Transformer questions

• posted

Greetings,

In reading up on my old power systems material, I have some questions (since I no longer have the professor's brain to pick).

For starters, let's say I have a transformer-based power supply/ system. Typically I have been looking at Y-D, Y-Y, D-D, D-Y configurations but I'm not particular about which one. If I hook a load up to a transformer that is rated in a particular way, what happens when the load draws less than the rated amperage, and what happens when it draws more (or attempts to draw more) than the rated amperage? In other words, in my reading, I am starting to see that one has to be very precise about the difference between what a system

*can* or *does* provide (i.e. maximum rating) vs. what it actually *does* provide when various loads are hooked up.

Second question, even dumber than the first one: If one "main function" of a transformer is to provide power through the means of two "physically disconnected" conductors (i.e. the coils), what does that buy you vs. just having a pair of conductors from the source? I think I have probably seen the information already that gives me my answer but I need a reminder. In other words, why bother with coils at all? Why not just have the ground and hot lines? (I'm speaking of a 1:1 transformer for the purposes of this argument.)

Third question: When banks of transformers are constructed and arranged at power stations, do they really take on a physical Y or D configuration, i.e. can you actually see them that way, or does their physical arrangement differ from the conceptual arrangement on a drawing?

Forgive me for this but these are the kinds of questions that fall through the cracks in my reading, i.e. I wonder about them now that I'm older and am able to think better about these topics than when I saw them the first time around.

Mike

• posted

Put crudely, it "buys you" either (a) not having to have a TV set that works on 11,000 volts or (b) accepting the consequences of 220 volt power distribution. Isn't that obvious?

• posted

And I said we're talking about a 1:1 transformer, i.e. that it neither steps up or steps down the supply voltage. In that case, what is the need to have the conductor be physically separate but electromagnetically coupled?

• posted

1:1 transformers are mainly used to obtain electrical isolation, eg to avoid shock hazards in particular situations.

• posted

And manners consist of telling someone to F off? Where'd you learn that, from Dick Cheney?

• posted

Rated amperage is the steady current the transformer can supply if it is "asked to", without overheating or letting the voltage drop below specs. It will supply only what it is "asked to" supply. It is the size of the load that determines how much current is "saked for".

Isolation. If you touch a live wire in the mains, you can get a shock. The current can travel from the live wire through your body and back to the source if you are grounded. If you isolate with a 1:1 transformer, you can touch a wire on the secondary (isolated) side and current cannot travel through your body back to the source even if you are grounded. If you touch _both_ wires than you can get a shock - the isolation doesn't protect you against that.

Don't know.

Ed

• posted

Thanks! That's what I was looking for. Also, I thought I read something about the isolation not just of current but some other phenomenon, but I can't recall what it is. Thanks for the help.

Mike

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