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

[jumper]

condensed version of relative portion
https://www.fsb.unizg.hr/usb_frontend/files/1508338227-0-elte_predavanje_03-dodatak.pdf

a split ph xfmr typ has 2 sec coils
they are connected in series (dot wise), low-dot-low-dot
one dot is a line hence the other dot is grounded
opposite phasing and hence polarity
it is not how you reference it
they are PHYSICALLY different
wound opposite hand relative to the primary and common ground reference

Nice link. Thanks.

The last line in your post is a bit confusing to me. Could you clarify for me.

 

[wvengineer]

Ummm (E)(I)=P therefore current is work

 

[mivey]

[I understand the phrase "change in polarity" to mean "multiply by -1".]

OK, then that's all you have with L1-N versus L2-N in 120V/240V split phase.

I think we can all agree that L1-N is in phase with N-L2, no phase difference. Reverse the terminals on the second measurement, and you have just introduced a change in polarity.

Cheers, Wayne

There are three terminals and two equal magnitude waveforms. We can all agree L1-N and L2-N have waveforms with a 180 degrees difference. Reverse the terminals on the 2nd measurement and you have changed the polarity so there are now two waveforms with a zero degree difference.

 

[mivey]

General Lectures on Electrical Engineering?

I don't remember.

 

[Besoeker]

There are three terminals and two equal magnitude waveforms. We can all agree L1-N and L2-N have waveforms with a 180 degrees difference. Reverse the terminals on the 2nd measurement and

Bbow up your scope leads.

 

[LarryFine]

How much can we complicate the simple? Egad! My opinions and observations, in no particular order:

We don't have to use the neutral as a reference; if we did, we'd never be able to make line-to-line voltage measurements.

If using L1 as the reference, nobody would argue there is a phase or timing issue when measuring to N or L2.

What changes when using N as the reference is instantaneous polarity, nothing else. The only thing shifted is probe location.

A dual-secondary transformer with the secondaries in series is electrically identical to a center-tapped secondary.

To function correctly, two secondaries must be wired "in phase" when wired in parallel, as well as when wired in series.

When using the neutral as the reference, the polarity is inverted, and resembles, but is not the same as, a 180-degree time shift.

If a person is standing, and does an about-face, they have made a 180-degree change, but that has nothing to do with time.

The D.C. analogy is suitable for this discussion, because the absolute polarity does not matter as long as both batteries are reversed.

If the two halves of a center-tapped secondary were genuinely out-of-phase, the line-to-line output would be zero volts.


Comments welcome.

 

[jaggedben]

Yes. It will show that, on a 120-0-120, the two 120V legs are 180° apart.

Or that one is the negative of the other. :roll::roll::roll:

 

[K8MHZ]

How much can we complicate the simple? Egad! My opinions and observations, in no particular order:

We don't have to use the neutral as a reference; if we did, we'd never be able to make line-to-line voltage measurements.

If using L1 as the reference, nobody would argue there is a phase or timing issue when measuring to N or L2.

What changes when using N as the reference is instantaneous polarity, nothing else. The only thing shifted is probe location.

A dual-secondary transformer with the secondaries in series is electrically identical to a center-tapped secondary.

To function correctly, two secondaries must be wired "in phase" when wired in parallel, as well as when wired in series.

When using the neutral as the reference, the polarity is inverted, and resembles, but is not the same as, a 180-degree time shift.

If a person is standing, and does an about-face, they have made a 180-degree change, but that has nothing to do with time.

The D.C. analogy is suitable for this discussion, because the absolute polarity does not matter as long as both batteries are reversed.

If the two halves of a center-tapped secondary were genuinely out-of-phase, the line-to-line output would be zero volts.


Comments welcome.

Liked by K8MHZ

 

[mbrooke]

Yes, they are aligned but still different. Different but still existent.

Two phases with a 120d difference produce positive pulses at different times. Sames for a 121d difference, 122d, 123d, ... 178d, 179d, AND 180d. One degree does not negate the phase difference and they still produce positive pulses at different times.

Most of the time we do not make use of this 180d difference and just use the individual phases alone as single-phase sources. Either the smaller phases or the larger phase.

A case where we do make use of the 180d difference producing positive pulses at different times is the 2-diode full-wave rectifier circuit using a center-tapped transformer.

Other cases include using the 180d positive pulses in a multi-phase inverter.

Just because the phases align does not negate the relationship.

Correct- for polarity, but power says otherwise. In in a system with a 5 degree phase difference one phase will give power when the other one does not.

 

[ggunn]

Comments welcome.

I say live it or live with it!

 

[ggunn]

Polarity doesn't really pertain to alternating quantities.

It does if you look at instantaneous values.

 

[jumper]

I say live it or live with it!

Works for me.:thumbsup:

 

[mivey]

How much can we complicate the simple? Egad! My opinions and observations, in no particular order:

We don't have to use the neutral as a reference; if we did, we'd never be able to make line-to-line voltage measurements.

Agree

If using L1 as the reference, nobody would argue there is a phase or timing issue when measuring to N or L2.

I would argue you are then measuring two different single phase signals: one at 120v and one at 240v.

What changes when using N as the reference is instantaneous polarity, nothing else. The only thing shifted is probe location.

Disagree. You have defined a different voltage system if the probe is defining your reference.

A dual-secondary transformer with the secondaries in series is electrically identical to a center-tapped secondary.

Agree.

To function correctly, two secondaries must be wired "in phase" when wired in parallel, as well as when wired in series.

Depends on your reference as to what "in phase" means. The definition is fundamental. The reference is key. Think about how you define your zero degree reference with a generator shaft and what you would have to do with the outputs from windings with a 180d orientation difference.

When using the neutral as the reference, the polarity is inverted, and resembles, but is not the same as, a 180-degree time shift.

The fascination with time shift again. We have a steady-state source. The underlying discussion revolves around two voltages with a 180d displacement. With a common generator shaft the time distraction goes away.

If a person is standing, and does an about-face, they have made a 180-degree change, but that has nothing to do with time.

Time between positive peaks is different. As evidenced by the time difference in positive pulses in a multi-phase converter. You are using a different voltage system configuration.

The D.C. analogy is suitable for this discussion, because the absolute polarity does not matter as long as both batteries are reversed.

The DC analogy does not work well because you are using static components with fixed voltage relationships to represent a time-varying system that has a continuous phase change and varying voltages.

If the two halves of a center-tapped secondary were genuinely out-of-phase, the line-to-line output would be zero volts.

Absolutely incorrect. That is equivalent to saying a 120 deg system has a line-to-line voltage of 120v instead of 208v.

 

[wwhitney]

OK, as a mathematician, let me observe the following:

For a function f(x): R -> R, the operations N(f)(x) = -f(x) and S_t(f)(x) = f(x + t) are two different operations. [I would call the first negation, and the second a shift of argument by t.] For the particular functions g(x) = Acos(wx+B), for any values of A, w, and B, it so happens that N(g) = S_pi/w(g). Thus when looking only at such functions g, it is impossible to tell if an operation or physical relationship corresponds to N or to S_pi/w.

Therefore if we want to distinguish between the two possibilities, we have to look at a broader range of input functions. For an arbitrary input waveform to a single phase transformer with center-tapped secondary, what is the relationship going to be between V_L1,N and V_L2,N? Is it going to be consistently V_L1,N = N(V_L2,N) or consistently V_L1,N = S_t(V_L2,N) for some value of t?

Cheers, Wayne

 

[Carultch]

OK, as a mathematician, let me observe the following:

For a function f(x): R -> R, the operations N(f)(x) = -f(x) and S_t(f)(x) = f(x + t) are two different operations. [I would call the first negation, and the second a shift of argument by t.] For the particular functions g(x) = Acos(wx+B), for any values of A, w, and B, it so happens that N(g) = S_pi/w(g). Thus when looking only at such functions g, it is impossible to tell if an operation or physical relationship corresponds to N or to S_pi/w.

Therefore if we want to distinguish between the two possibilities, we have to look at a broader range of input functions. For an arbitrary input waveform to a single phase transformer with center-tapped secondary, what is the relationship going to be between V_L1,N and V_L2,N? Is it going to be consistently V_L1,N = N(V_L2,N) or consistently V_L1,N = S_t(V_L2,N) for some value of t?

Cheers, Wayne

V_L1,N = N(V_L2,N), would be most correct in the general sense of an arbitrary waveform.

The voltage differences add up to the total voltage on the secondary coil, and measured from the center tap, are equal and opposite.

Suppose you define V1 = 4, V2 = 8, and define N to be the midpoint of V1 and V2. The meaning of zero is arbitrary, as it is differences that will matter. Thus N would equal 6. Observe that V2-N = +2, and V1-N = -2.

Now generalize this problem.
N = (V1 + V2)/2
V1n = V1-N
V2n = V2-N

V1n = V1-(V1 + V2)/2
V2n = V2-(V1 + V2)/2

Test the relationship that voltages relative to N are equal and opposite.
V1n =?= -V2n
V1-(V1 + V2)/2 =?= -(V2-(V1 + V2)/2)
V1-(V1 + V2)/2 =?= (V1 + V2)/2 - V2

V1 =?= 2*(V1+V2)/2 - V2
V1 =?= V1 + V2 - V2
V1 = V1

 

[winnie]

Okay, how about this one:

Vector representation of values in AC circuits is one of the 'tools of the trade'. It is used to represent voltage, current, impedance, and a host of other values.

Such representation has its limits of applicability, for example sometimes limiting use to a single frequency sine wave.

The vector representation of sine wave phase clearly covers all 4 quadrants of the plane, 0 to 360 degrees. 180 degrees of phase is _different_ from 0 degrees of phase.

Weather two separate circuits with a 180 degree phase difference 'count' as two separate phases depends upon the application.

If you application is making a rotating magnetic field, then such a pair of circuits is a single phase.

-Jon

 

[jaggedben]

...

For a function f(x): R -> R, the operations N(f)(x) = -f(x) and S_t(f)(x) = f(x + t) are two different operations. [I would call the first negation, and the second a shift of argument by t.] For the particular functions g(x) = Acos(wx+B), for any values of A, w, and B, it so happens that N(g) = S_pi/w(g). Thus when looking only at such functions g, it is impossible to tell if an operation or physical relationship corresponds to N or to S_pi/w.

Therefore if we want to distinguish between the two possibilities, we have to look at a broader range of input functions. For an arbitrary input waveform to a single phase transformer with center-tapped secondary, what is the relationship going to be between V_L1,N and V_L2,N? Is it going to be consistently V_L1,N = N(V_L2,N) or consistently V_L1,N = S_t(V_L2,N) for some value of t?

Cheers, Wayne

:thumbsup:

 

[buffalonymann]

Nope.
If you have the same load across each of the L-N 120V legs the current in the neutral will be zero.

:slaphead: well now, I see you haven't read or maybe comprehended my previous statements, in them I had explained why there is no current on the neutral. when you have two equal loads across l1-n and l2-n you've created a series circuit and the current is found on l1 and l2. this is simple to verify

I also explained why only the imbalance shows up on the neutral - the remainder is a series circuit across the 240. wouldn't it be great if the currents just disappeared like you think they do....electric bill would be zero

 

[buffalonymann]

How much can we complicate the simple? Egad! My opinions and observations, in no particular order:

We don't have to use the neutral as a reference; if we did, we'd never be able to make line-to-line voltage measurements.

If using L1 as the reference, nobody would argue there is a phase or timing issue when measuring to N or L2.

What changes when using N as the reference is instantaneous polarity, nothing else. The only thing shifted is probe location.

A dual-secondary transformer with the secondaries in series is electrically identical to a center-tapped secondary.

To function correctly, two secondaries must be wired "in phase" when wired in parallel, as well as when wired in series.

When using the neutral as the reference, the polarity is inverted, and resembles, but is not the same as, a 180-degree time shift.

If a person is standing, and does an about-face, they have made a 180-degree change, but that has nothing to do with time.

The D.C. analogy is suitable for this discussion, because the absolute polarity does not matter as long as both batteries are reversed.

If the two halves of a center-tapped secondary were genuinely out-of-phase, the line-to-line output would be zero volts.


Comments welcome.

What amuses me is that electricians understand this simplicity, but those claiming to be engineers do not. It tells me they don't even know what they looking at with a scope:jawdrop:

 

[buffalonymann]

To exchange enegy requires both an electric and magnetic field (voltage and current).

The cross product produces the Poynting Vector and shows the direction of energy flow.

current is not a magnetic field
current is the resultant work performed due to emf