Loose neutral

[don_resqcapt19]

230722-21212 EDT

don_resqcapt22:

Your understanding of multiple phases is incorrect. Your approach would flunk you in an elementary course in a basic college AC circuit class.

Do you have available a scope with at least two vertical channels, and a single shot time based channel. The horizontal channel would be a linear sweep vs time, and the vertical channels would be the signals you want to look at vs time.

The horizontal channel is triggered by a signal. This trigger is usually selected from one of the vertical channels, the AC line, or an external source. Also the horizontal sweep can come from an external signal, an internal sweep generator, and the internal linear time sweep can be repetitive, synced or free running, or single shot. single shot would be triggered from some source.

Best to operate under battery mode, or open the EGC path in the AC power cord.

For 60 Hz tests as a starter it is good to use 2 mS or 5 mS time base per major division. Use 10X probes if you are going to look at 120 signals.

Connect the scope common to the center tap of your source voltage.

Label the transformer output terminals, the hot ends, as A and B, and the center tap as N.

Connect the scope common to N.

Connect scope external sync to A with appropriate attenuation. This makes the scope sync common to Channel A. Connect scope probe 1 to A, and adjust sync phasing so that left most half sine wave, relative to sync point, is positive on the screen. Some scopes allow you to adjust the sync start point to the right of the left side of the display.

If you can do this report back.

.

Thank you for your assessment of my knowledge, it has the same value to me as what I paid for that assessment

 

[gar]

230813-2059 EDT

don_resqcapt19:

Many of your comments appear to be correct, but you are entirely wrong in you thinking about the signals from a centered tapped single phase transformer.

You probably don't have a two or more Y channel scope. If you had one of these, then you could look at actual waveforms vs time.

Without such instrumentation you can still do experiments with an AC voltmeter that will demonstrate the same information.

Suppose you get a transformer with two equal voltage secondaries.

If you wire these secondaries in series one way you get twice the output voltage of a single secondary. If you try to connect the two hot wires you will get big sparks and blow an input fuse.

If instead you reverse the polarity of one secondary winding so both windings are in phase, then you can parallel the two windings with virtually no sparks, and you won't blow an input fuse.

In both cases the same maximum power can be transferred from input to output, just at different voltage levels.

.

 

[GoldDigger]

That is right, my thinking was bad in that way as well. But the concept of putting loads on both A and B to see the imbalance is valid. They definitely need to be different resistances though.

And the easiest way to get the two loads to have different resistances is to have one load be infinite resistance and just move the other load from one line to the other to complete the test.
A voltage drop on the loaded side can result from either a high resistance hot or a high resistance neutral. The definitive indicator of a high resistance neutral is that the line to neutral voltage increases on the unloaded side.

 

[GoldDigger]

"one is the inverse of the other,or a 180 degree phase shift"

one is the inverse of the other, or an APPARENT 180 degree phase shift

as I stated before, in a balanced system, the two are impossible to distinguish, one from the other.

I disagree, and I assert that the two are impossible to distinguish when the applied voltage is a single frequency sine wave rather than a complex wave form.

For a complex wave form, the concept of a 180 degree phase shift is ambiguous. Individually phase shifting each component sine frequency by 180 will yield a different result from applying a time offset equal to 1/2 the period of the fundamental frequency.

 

[don_resqcapt19]

230813-2059 EDT

don_resqcapt19:

Many of your comments appear to be correct, but you are entirely wrong in you thinking about the signals from a centered tapped single phase transformer.

You probably don't have a two or more Y channel scope. If you had one of these, then you could look at actual waveforms vs time.

Without such instrumentation you can still do experiments with an AC voltmeter that will demonstrate the same information.

Suppose you get a transformer with two equal voltage secondaries.

If you wire these secondaries in series one way you get twice the output voltage of a single secondary. If you try to connect the two hot wires you will get big sparks and blow an input fuse.

If instead you reverse the polarity of one secondary winding so both windings are in phase, then you can parallel the two windings with virtually no sparks, and you won't blow an input fuse.

In both cases the same maximum power can be transferred from input to output, just at different voltage levels.

.

what ever you say!

 

[gar]

230821-1734 EDT

don_resqcapt19:

It is not what I say, but what you can experimentally demonstrate for yourself.

Find a small transformer, like 100 to 200 watt capacity. This should have two separate secondaries of equal voltage and current rating. This provides a means to connect the secondaries in series or parallel.

First, connect the secondaries in series. This means the two voltages are additive. Thus, a voltage measurement across the two unconnected leads is 2 times the voltage of a single secondary. Short the 2 unconnected leads together, and you will get big sparkes, and high current running thru the secondaries, and blow a primary fuse.

Second, instead reverse the polarity of one secondary. Now read the voltage difference between the 2 unconnected leads, and the voltage difference will be near 0. Connect the 2 open leads together, and there will be little arcing, and you will not blow an input fuse.

This is clear cut experimental evidence of what happens.

.

 

[winnie]

I am looking at live video from Barcelona, Spain. The sun is high in the sky. I am also looking at live video from Honolulu, HI. The sky is dark. Is the time different in these two measurements?

Clearly if I measure L1-N and L2-N simultaneously using two channels of an oscilloscope, there is no time difference in those measurements. The measurements have been made at the same instant(s) in time.

However if the waveform itself is being used as your time reference, the L1-N and L2-N measurements are displaced in time. As I've said before, and others have said in this thread, the inversion which is the electrical basis of producing L1-N and L2-N is indistinguishable from a 180 degree time shift between the two waveforms, in the limit of a pure single frequency sine wave. However the mechanism for producing these two waveforms is an inversion, not an actual time shift.

Once could imagine a system where there is an actual time shift. If you compare an inversion system to a system with a time delay of 1/2 fundamental cycle, then you won't be able to distinguish a single frequency sine wave, but you will be able to distinguish any waveform which has 2n * fundamental frequency components.

-Jon

 

[don_resqcapt19]

230821-1734 EDT

don_resqcapt19:

It is not what I say, but what you can experimentally demonstrate for yourself.

Find a small transformer, like 100 to 200 watt capacity. This should have two separate secondaries of equal voltage and current rating. This provides a means to connect the secondaries in series or parallel.

First, connect the secondaries in series. This means the two voltages are additive. Thus, a voltage measurement across the two unconnected leads is 2 times the voltage of a single secondary. Short the 2 unconnected leads together, and you will get big sparkes, and high current running thru the secondaries, and blow a primary fuse.

Second, instead reverse the polarity of one secondary. Now read the voltage difference between the 2 unconnected leads, and the voltage difference will be near 0. Connect the 2 open leads together, and there will be little arcing, and you will not blow an input fuse.

This is clear cut experimental evidence of what happens.

.

That clearly proves my point that the windings in the center tapped transformer are not 180° out of phase with each other as the voltages are additive as in you first connection. You physically reversed the connection in the second case to make the voltages out of phase by 180 degrees to make it a subtractive connection.

 

[gar]

230823-1042 EDT

don_resqcapt19:

In general you seem to have a reasonably good understanding of circuit theory.

But in the case of the center tapped secondary you are wrong.

The terminology in AC circuitry theory where you have sine waves of the same frequency, phase, and amplitude, and you overlay one on the other "in phase" means that both waveforms will look identical. Furthermore if you parallel these two signals there will be no circulating current between the transformers.

A convention to indicate phasing of transformers is to put a "DOT" next to all the leads that have the same phase.

.

 

[winnie]

IMHO the concept of 'in phase' is somewhat context dependent. In some contexts, two waveforms with the same zero crossing times are in phase, in other contexts they are 'antiphase'. But two waveforms with a 180 degree phase difference are more closely connected than two waveforms with (say) a 120 degree phase difference.

Consider a stator coil in a motor. The wire enters a slot, exits the slot at the far end of the stator, travels around the periphery (the 'end turn'), enters a different slot from the far end of the stator, exits the slot at the near end of the stator, and then travels around the near side periphery back to the first slot. This continues for some number of turns, and then the wire finally exits the second slow and move on to a different part of the motor.

Current flow in the entire wire is (and must be) perfectly in phase. Yet in a very real sense the current flow in the first slot is 180 degrees out of phase with the current flow in the second slot. The 'net slot current' must be in opposite directions and thus must be perfectly out of phase.

 

[gar]

230824-0755 EDT

To make the discussion simple I assume we are dealing with a comparision of two sine waves of equal frequency, stable phase relationship, equal voltage and identical zero crossing times. If two waveforms have the same zero crossing slope, then they are "IN PHASE".. If one waveform has its zero crossing slope opposite the other, then the two waveforms differ by 180 degrees. It is just that simple.

.

 

[winnie]

Again I say that this is context dependent.

I absolutely agree that the two since functions you describe have a phase angle difference of 180 +- n*360 degrees.

But in the context of (for example) creating a rotating field in a motor, those two sine waves are 'in phase'.

Yet in the context of current balance on a neutral node, the two sine functions you describe are optimally 'out of phase'.

So I will stipulate a 180 degree phase difference for an inversion, but still claim that this is 'in phase' depending upon context.

Jon

 

[gar]

230824-1110 EDT

winnie:

In a motor or other electro-magnetic structure the direction of the resultant magnetic field from a coil will be dependent upon how the coil is connected, and/or the direction of winding the coil, or the direction of the current thru the coil.

.