K8MHZ
Senior Member
- Occupation
- Electrician
I guess I misunderstood you. I thought that you were trying to say that there was more than one phase.
Sorry.....
Why is residential wiring known as single phase?
- Thread starter TimWA
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I guess I misunderstood you. I thought that you were trying to say that there was more than one phase.
Sorry.....
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
120130-1601 EST
K8:
Yes for #73.
How much does voltage vary at your home? Do you have any plots thru the day?
Not intended to have any bearing on this thread.
.
K8:
Yes for #73.
How much does voltage vary at your home? Do you have any plots thru the day?
Not intended to have any bearing on this thread.
.
kwired
Electron manager
- Location
- NE Nebraska
Listen up!
Listen up!
Hear! Hear! The Brit tells it right! Very succinctly too.
An understanding of trig would be helpful here. Wouldn't hurt to know phasor math as well.
``120Vrms @ 180 <-----0----->120Vrms @ 0
````````````````------------>240Vrms @ 0
``240Vrms @ 180 <------------
Listen up!
Hear! Hear! The Brit tells it right! Very succinctly too.
An understanding of trig would be helpful here. Wouldn't hurt to know phasor math as well.
``120Vrms @ 180 <-----0----->120Vrms @ 0
````````````````------------>240Vrms @ 0
``240Vrms @ 180 <------------
quogueelectric
Senior Member
- Location
- new york
Phase Craze....
Phase Craze....
Picture a single winding with a center tap intentionally grounded.... Now freeze in time when the voltage reaches +120v to ground/neutral/center tap +171 volts peak for 120v rms. The black lead of the dc meter is connected to the center tap/neutral the red lead reads +120v dc...... Now if you swing the red lead ALL the way over to the other side of the winding you will read -120v to Neutral/ground/center tap. Just like two batteries in series the voltage from -120 volts to +120 will add up to 240volts which is the voltage measured across the entire coil. What confuses many people is there is no time reference with a simple ac meter the a side of the winding is positive when the b side is negative making the voltages additive with reference to the entire coil. When you measure from the center tap you are effectively reversing the leads giving you a positive and a negative value to two batteries in series measuring with the black lead at the midpoint between the two batteries. Hence it is really NOT 2 phases just like 2 batteries in series are not 2 phases.
Phase Craze....
Picture a single winding with a center tap intentionally grounded.... Now freeze in time when the voltage reaches +120v to ground/neutral/center tap +171 volts peak for 120v rms. The black lead of the dc meter is connected to the center tap/neutral the red lead reads +120v dc...... Now if you swing the red lead ALL the way over to the other side of the winding you will read -120v to Neutral/ground/center tap. Just like two batteries in series the voltage from -120 volts to +120 will add up to 240volts which is the voltage measured across the entire coil. What confuses many people is there is no time reference with a simple ac meter the a side of the winding is positive when the b side is negative making the voltages additive with reference to the entire coil. When you measure from the center tap you are effectively reversing the leads giving you a positive and a negative value to two batteries in series measuring with the black lead at the midpoint between the two batteries. Hence it is really NOT 2 phases just like 2 batteries in series are not 2 phases.
But, if the two voltages are at different potentials wrt neutral, you can't reasonably say that they are in phase.
And if they are not in phase..........
quogueelectric
Senior Member
- Location
- new york
in phase
in phase
In phase to me means assigning a time reference which is moving forward unless the universe is expanding so fast that we are approaching the speed of light when time will come to a halt. However as for tomorrow unless the Mayans come back then by measuring both sections of the coil holding the meter leads red to black + to - they will read as two 120 volt sine waves with the same amplitude in exactly the same time I say TIME frame. Just as measuring two batteries in series. The voltage across the entire coil will be 240 and in the same phase /time reference because it is in fact the same coil. The two separately measured coil sections have to rise and fall in unison because they are the same coil.
in phase
In phase to me means assigning a time reference which is moving forward unless the universe is expanding so fast that we are approaching the speed of light when time will come to a halt. However as for tomorrow unless the Mayans come back then by measuring both sections of the coil holding the meter leads red to black + to - they will read as two 120 volt sine waves with the same amplitude in exactly the same time I say TIME frame. Just as measuring two batteries in series. The voltage across the entire coil will be 240 and in the same phase /time reference because it is in fact the same coil. The two separately measured coil sections have to rise and fall in unison because they are the same coil.
For me, and I suspect a great many others in this field, for two sinewave voltages to be in phase they need have equal frequency, cross zero at the same instant in time and have peak positive magnitude at the same instant in time.
Without that, they are not in phase.
T
T.M.Haja Sahib
Guest
The problem has arisen due to the wrong assumption that there is a reversal of the voltage vector from one set of outer conductor -neutral to the second set of outer conductor-neutral in a 120v/240v power system.In fact the two 120v voltage vectors are in phase.This can easily verified by checking the currents in the outer conductors:the two currents will be 180 degree out of phase!
quogueelectric
Senior Member
- Location
- new york
They do all of these thing that you are saying most people are reversing the leads of the measuring instrument because the winding is center tapped if you reverse the leads you effectively cause a 180 degree phase shift just as if you turn around you view a 180 degree different view but you are standing in the same spot.
If you measure wrt the centre-tap, the two voltages are phase displaced by 180deg as shown on my diagram in post #31.
That's what you would see on an oscilloscope.
T
T.M.Haja Sahib
Guest
Please see post#39
Have you measured the currents in two outer conductors and the neutral ?
What conclusion may drawn based on these currents?
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T
T.M.Haja Sahib
Guest
The correct potentials in your 'more usual arrangement'above is L1=240v(with respect to L2), N=120v(with respect to L2) and L2=0V.It does not matter 'N' is grounded or not.If they were in phase the neutral current double assume the same load on both windings. And you wouldn't have 240V end to end.
The more usual arrangement:
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With respect to what is it 0V?
I agree. And I not made any comment about grounding. It is irrelevant to this discussion.
T
T.M.Haja Sahib
Guest
I said 'potential'.The potential of' 'N' can be arbitrary,because only potential difference counts.
You comment on the "correct" potentials as L1 being 240V and L2 being 0V.
You could but I think it would more commonly be considered 120V-0-120V for obvious reasons in the application being discussed here.
T
T.M.Haja Sahib
Guest
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Back to the OP's question:
Back to the OP's question:
There are "phases" and "phase angles". A "phase" (noun) must be generated by its own generator. A "phase angle" (adjective) can be obtained with only transformers. For example, the 208V seen in the high leg delta configuration carries a 90 degree "phase angle" and is not a 4th phase. Likewise the 120V @ 180 seen on L2 is obtained from a transformer and is not a 2nd "phase", although the term is used loosely by some..
Back to the OP's question:
There are "phases" and "phase angles". A "phase" (noun) must be generated by its own generator. A "phase angle" (adjective) can be obtained with only transformers. For example, the 208V seen in the high leg delta configuration carries a 90 degree "phase angle" and is not a 4th phase. Likewise the 120V @ 180 seen on L2 is obtained from a transformer and is not a 2nd "phase", although the term is used loosely by some..
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