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

[ggunn]

same for 3 phase
although it occurs simutaneously it is seperated by Pi or 8.33 mS timescale NOT time

But there is no single input waveform in 3 phase. If one phase glitches the other two don't, at least not as a direct result.

 

[Ingenieur]

But there is no single input waveform in 3 phase. If one phase glitches the other two don't, at least not as a direct result.

sure it does
minus propagation delay (but same for a 120 fault on a 120/240/1 system)

 

[wwhitney]

The point Wayne is trying to make, is that it is more correct to negate, than it is to phase shift, when calculating instantaneous L2n from known instantaneous L1n. It is a coincidence that it is also correct to phase shift in the special case of the sine waveform, but in the case of a generalized waveform, it isn't.

Precisely.

Cheers, Wayne

 

[Ingenieur]

The point Wayne is trying to make, is that it is more correct to negate, than it is to phase shift, when calculating instantaneous L2n from known instantaneous L1n. It is a coincidence that it is also correct to phase shift in the special case of the sine waveform, but in the case of a generalized waveform, it isn't. That is, based on the nature of how a split phase source is produced. A sawtooth wave is an example where phase shifting by 180 degrees alone, will get the wrong answer.

not really
1 we are discussing 120/240/1 60 Hz sinusoidal waveform
2 BOTH are equally correct since when you use phasors/trig the result is negation in this special case, so perhaps the 180 is MORE CORRECT than negation?

try that with 3 ph, so good for 3 phase 0/120/240 deg but not 0/180?
nope, not buying it

 

[Ingenieur]

this thread is number 9 for replies in this section
number 8? single phase or 2 phase....lol

 

[jumper]

this thread is number 9 for replies in this section
number 8? single phase or 2 phase....lol

Me no understand?

 

[Ingenieur]

Me no understand?

if you go to the forum section 'elec calcs/engr'
tap the reply column
it sorts by number of replies
this is the 9th highest with 26x
number 8 is a similar topic, a locked thread titled 'single or 2 phase' 304 replies

 

[ggunn]

sure it does
minus propagation delay (but same for a 120 fault on a 120/240/1 system)

The three phases are created independently; they do not result from a single phase. They never were the same phase so they didn't get where they are by "phase shifting". They were created 120 degrees apart, i.e., they were not created at the same time.

A glitch on the single phase from which split phase is made will cause a simultaneous glitch on L1 and L2. There is no analog of that effect in 3 phase. Sure, a mechanical jitter on a turbine will have a simultaneous effect on all three phases of 3 phase but the linkage is mechanical.

If you are saying that neither 3 phase nor split phase has anything to do with phase shifting, then yes, I agree.

 

[Ingenieur]

The three phases are created independently; they do not result from a single phase. They never were the same phase so they didn't get where they are by "phase shifting". They were created 120 degrees apart, i.e., they were not created at the same time.

A glitch on the single phase from which split phase is made will cause a simultaneous glitch on L1 and L2. There is no analog of that effect in 3 phase. Sure, a mechanical jitter on a turbine will have a simultaneous effect on all three phases of 3 phase but the linkage is mechanical.

If you are saying that neither 3 phase nor split phase has anything to do with phase shifting, then yes, I agree.

doesn't matter
on 3 ph a slg fault will be reflected in the other phases
they are interconnected either wye or delta, not independent

 

[roger]

if you go to the forum section 'elec calcs/engr'
tap the reply column
it sorts by number of replies
this is the 9th highest with 26x
number 8 is a similar topic, a locked thread titled 'single or 2 phase' 304 replies

This thread will never come close to the #1 longest, it was 2,567 posts The second post should have been where it stopped but noooooooooo. I don't think we could stand that many repeats, thoughts, and circular conversations again. :lol:

Roger

 

[Ingenieur]

This thread will never come close to the #1 longest, it was 2,567 posts The second post should have been where it stopped but noooooooooo. I don't think we could stand that many repeats, thoughts, and circular conversations again. :lol:

Roger

:lol:

 

[ggunn]

doesn't matter
on 3 ph a slg fault will be reflected in the other phases
they are interconnected either wye or delta, not independent

Then you are saying that phase shift isn't involved in three phase, either. I agree.

 

[LarryFine]

no, it is not a choice
the neut is the 'common' or reference or 'negative' and polarity should be observed

Then you will knowingly be scoping signals of opposing polarity, or phase if you prefer to call it that, and will knowingly observe two sine waves that appear to resemble a [air of waves that are 180 degrees out of sync, or step (in time), but are actually 180 degrees in opposition, or polarity, at the same time, or in step.

 

[LarryFine]

Most two channel 'scopes have a common ground terminal for each. If you want to measure the two aides of the 120-00-120 simultaneously to compare them. using the neutral as the common is the only choice.

See above response. You should know why you are observing opposing waves.

 

[LarryFine]

• 

To me, this is wrong. Looking at the two smaller sine waves, the line-to-line output would be zero.

 

[LarryFine]

Polarity signs like + and - don't sit well with alternating voltages.

At one given moment in time, they do, and only instantaneous polarity can be observed. Time must be added to the equation (pun intended) in order for what appears to be a 180-degree offset to be observed.

 

[LarryFine]

For those who missed my statement - L1 is positive and L2 is negative therefore potential is 240 volts. It has to be this way or no current will flow, it has to be this way or Michael Faraday and Joseph Henry are frauds. Ok now that is settled; L1 is positive and N is negative at the very same time that N is positive with respect to L2.

I concur.

 

[LarryFine]

Why the L2-N prediction? They are separate waveforms and are rarely mirrors of each other and practically never exact matches. Or is it more of an academic question?

But they aren't mirror images; if they were, we'd have two 120v outputs but no 240v output.

The -1 multiplier is okay, but it doesn't really show that we are taking the start of the 1st waveform to be 8.333 ms before the 2nd waveform.

Therein lies the disagreement: We should be taking the start of both waveforms simultaneously.

We have defined the positive direction to be away from the center. The first waveform begins a positive rise from zero away from center then 8.333 ms later the second waveform begins a positive rise away from center.

No, we haven't defined the positive direction to be away from the center tap. We (the "opposition") are saying one line is positive while the other is negative. Yes, we realize they both will be of opposite polarity (or "direction" if you prefer) 8.333 ms later.

 

[LarryFine]

An 8.333 ms delay.

That has the same effect, only with the passage of time, as the -1 multiplier, which works equally well with or without the passage of time.

 

[LarryFine]

note each 3 ph line is labelled '+'
but you have v across them

You must add the timing vector into the mix for that to be possible. Even the standard image of three overlapped sine wave doesn't purport all three phases to be positive at the same time.