May I ask a question about the single vs two phase stuff

[jumper]

That isn't clarifying the question. It's changing it. The question was whether 'polarity' belongs in the discussion. And it certainly does.

Polarity does, but in context/reference.

 

[Besoeker]

Polarity does, but in context/reference.

OK. For 120-0-120 you have L1, N, and L2.
Which one is positive?

 

[jumper]

OK. For 120-0-120 you have L1, N, and L2.
Which one is positive?

In reference to how it is built or how I reference it on on a two channel scope?

Individualy they are built in phase with the secondary in series, one phase double,but I analyze it from a common reference, da noodle. two phases opposite.

 

[Besoeker]

In reference to how it is built or how I reference it on on a two channel scope?

Individualy they are built in phase with the secondary in series, one phase double,but I analyze it from a common reference, da noodle. two phases opposite.

So how can you call any of them positive when they are negative half the time?

 

[mivey]

OK, crazy question for the thread.

Instead of using meters and scopes to determine a 'direction' of flow, why not use a compass? The compass won't need to pick a spot on the coil for a reference.

Of course, this would take a slow version of AC to see the compass needle move.

If we put a compass on each side of the 240 volt coil, one for each 120 volt section, would the compasses point in the same direction as they went from one cycle to the next, or would they be 'out of phase' and point at opposite directions?

Funny you should ask.

Like a voltage, it depends on your reference.

If I put N on the equator and L2 North, then the compass points North from L1-N and North from N-L2 (0 phase difference).

If I put N on the North Pole, then the compass points North from L1-N and North from L2-N (180 phase difference).

You pick the reference. Either way is valid. It really is that simple.

 

[jumper]

So how can you call any of them positive when they are negative half the time?

Ya lost me. Negative (opposite/anti/etc) phase angle, not magnitude.

 

[Besoeker]

Funny you should ask.

Like a voltage, it depends on your reference.

If I put N on the equator and L2 North, then the compass points North from L1-N and North from N-L2 (0 phase difference).

If I put N on the North Pole, then the compass points North from L1-N and North from L2-N (180 phase difference).

You pick the reference. Either way is valid. It really is that simple.

Since the whole thing reverses every 8.33 ms the poor compass would know what to do.............

 

[Besoeker]

Ya lost me. Negative (opposite/anti/etc) phase angle, not magnitude.

Each is positive for half a cycle and negative for half a cycle. How can you reasonably call any of them positive or negative?
We are not discussing DC here.

 

[mivey]

OK. For 120-0-120 you have L1, N, and L2.
Which one is positive?

The missing links: at what times of interest and is current leaving or entering the terminal then?

 

[mivey]

So how can you call any of them positive when they are negative half the time?

You pick a point in time and define directions. They are relative but selected by you for a specific instant.

 

[Besoeker]

The missing links: at what times of interest and is current leaving or entering the terminal then?

The quantities are RMS. Not instantaneous. You simply can't pick a single instantaneous point on a waveform to determine phase relationships.

 

[jumper]

Each is positive for half a cycle and negative for half a cycle. How can you reasonably call any of them positive or negative?
We are not discussing DC here.

If you model them as as independent sources they are in phase. The Tutorial shows that.

How did DC get into this?

 

[mivey]

The quantities are RMS. Not instantaneous. You simply can't pick a single instantaneous point on a waveform to determine phase relationships.

That is what you do with relaying. You have to define the system senses.

Add: read the beginning of Blackburn's relaying book. He covers arrows, directions, +/-, conventions, etc.

 

[winnie]

If you model them as as independent sources they are in phase. The Tutorial shows that.

How did DC get into this?

The + and - symbols in the diagram.

Besoeker is reading them as DC + - symbols, in which case they are clearly incorrect, because this is AC. In other words if + and - indicate the voltage of the terminal, then I agree with Besoeker, that is incorrect because AC does not have polarity.

I am reading them as indicating the polarity of a measuring instrument connected to the terminals. Consider an isolated oscilloscope (isolated so that you don't have to work about terminal grounding and ground loops). You have two leads. When lead A is positive relative to lead B, then the scope trace is deflected upward on the screen. When lead A is negative with respect to lead B then the scope trace is deflected downward. The polarity of your scope leads needs to be indicated if you want to be able to talk meaningfully about a waveform being inverted.

I believe that the + and - are being used to indicate the sense (polarity) of the _measurement_, but agree that it would be clearer if some other indication were used.

-Jon

 

[jumper]

The + and - symbols in the diagram.

Besoeker is reading them as DC + - symbols, in which case they are clearly incorrect, because this is AC.

I am reading them as indicating the polarity of a measuring instrument connected to the terminals. Consider an isolated oscilloscope (isolated so that you don't have to work about terminal grounding and ground loops). You have two leads. When lead A is positive relative to lead B, then the scope trace is deflected upward on the screen. When lead A is negative with respect to lead B then the scope trace is deflected downward. The polarity of your scope leads needs to be indicated if you want to be able to talk meaningfully about a waveform being inverted.

I believe that the + and - are being used to indicate the sense (polarity) of the _measurement_, but agree that it would be clearer if some other indication were used.

-Jon

Agree. I did not draw it! Some under paid, under stress, undergrad prolly did..

 

[jumper]

Agree. I did not draw it! Some under paid, under stress, undergrad prolly did..

Like this pic. Context and reference.:angel:



It really is that simple.....

 

[LarryFine]

Are you referring to additive and subtractive polarity between primary and secondary windings or series and parallel of the secondary?

I'm referring only to secondary windings.

Bes, please clarify, with pic, which diagram I posted that you have objections with.

Larry, ditto please.

This the pic you guys wanna discuss?

Yes, this one. To me, the two sine waves are incorrect. They should be oriented "in sync" to match the + and - symbols. When someone says that they're accurate as seen by a 'scope from the neutral, I say "That's because you're only relocating one probe, not both."

 

[LarryFine]

OK. For 120-0-120 you have L1, N, and L2.
Which one is positive?

At a frozen-in-time (1/2 cycle) moment, L1 is positive and N is negative, and sat the same time, N is positive and L2 is negative. Overall, L1 is positive and L2 is negative. Just like two batteries in series.

1/2 cycle later, everything is reversed, which is okay, because it's all reversing in sync, or in phase. Just like two batteries in series that are both being reversed in sync, or in phase. The voltages are additive.

 

[LarryFine]

In reference to how it is built or how I reference it on on a two channel scope?

I refer to how it's built, or wired.

Individually they are built in phase with the secondary in series, one phase double,but I analyze it from a common reference, da noodle. two phases opposite.

Well, stop doing that!

 

[LarryFine]

How did DC get into this?

That was my doing, I guess. Use two batteries that you flip in their holders 120 times per second.