phases

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Besoeker3 said:
I'm glad it is simpler for us UKIPERs. Domestic is single phase 230V. Industrial is 3-phase 400V. Job done!
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But when your part of the world was being electrified, Edison's 110V was a legacy system. The AEG choice of 220V then was better/a improvement. But to use absolutely terrible English, it ain't gonna change. :D
 
paulengr said:
The neutral is a phase conductor. It is conducting amps. It is only “zero Volts” because we always measure Voltage with respect to another point. And guess what happens if the utility loses the neutral? Same as a phase conductor…some circuits are affected, some aren’t.
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And that "other point" we read zero volts to is "ground". We read that because we intentionally ground that neutral, NEC tells us that is the conductor to be grounded when it is present in the system, otherwise one could ground any conductor of the system, and that is kind of what happens on systems with no neutral, such as two wire systems or three phase three wire delta systems.
 
norcal said:
But when your part of the world was being electrified, Edison's 110V was a legacy system. The AEG choice of 220V then was better/a improvement. But to use absolutely terrible English, it ain't gonna change. :D
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Was there ever two phase systems (real two phase systems and not just any combination of two ungrounded conductors with a grounded conductor) across the pond?
 
paulengr said:
Ok so what about motors over say 400 kW where you need to go to higher voltages?

And I wouldn’t say it’s that easy. RCDs aren’t used in many parts of the world and neither are loop tests,
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Not a problem. We have used 690V, 3.3kV, and 11kV.
 
Some may find it interesting that virtually all digital communications products today use 90° 2-phase for modulating and demodulating the signals. That includes, 3G, 4G, & 5G cellphones, Wi-Fi access points, fiber and cable modems, digital broadcast TV and satellite TV, etc. Instead of 60 Hz, the carrier frequency is often in the GHz range, but the modulated signals can be represented as vectors on the same "complex plane" that we use for polyphase power systems. It's just that they wiggle around a lot faster. ;)
 
synchro said:
Some may find it interesting that virtually all digital communications products today use 90° 2-phase for modulating and demodulating the signals. That includes, 3G, 4G, & 5G cellphones, Wi-Fi access points, fiber and cable modems, digital broadcast TV and satellite TV, etc. Instead of 60 Hz, the carrier frequency is often in the GHz range, but the modulated signals can be represented as vectors on the same "complex plane" that we use for polyphase power systems. It's just that they wiggle around a lot faster. ;)
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Not the same. Say we have a single carrier signal (not OFDM) such as 8x8 QAM. We pick ONE amplitude and phase angle from a large list of choices like these diagrams:


Now the interesting thing is let’s say I start with a carrier and I only amplitude modulate it. So say I have a choice of 0 or 180 degrees phase angle and 4 possible amplitude levels giving us 8 possibilities. If we take a second signal of the same design but 90 degrees offset and add them, we get 256 QAM but the modulator circuit has two parallel paths. The output is still both amplitude and phase modulated but now with 256 possibly phase angles and amplitudes. It’s not that two phases exist. It’s just a mathematical convenience of the complex algebra involved. In OFDM we add together multiple frequencies at once. The spectrum looks nothing like QAM but again we are modulating both amplitude and phase angle but looking at it from this perspective is messy at best.

This is very different from power transmission where we never add phases except rotations in phase shifting transformers. At best OFDM is sort of related to harmonic analysis.
 
synchro said:
Some may find it interesting that virtually all digital communications products today use 90° 2-phase for modulating and demodulating the signals.... Instead of 60 Hz, the carrier frequency is often in the GHz range, but the modulated signals can be represented as vectors on the same "complex plane" that we use for polyphase power systems. It's just that they wiggle around a lot faster. ;)
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paulengr said:
Not the same. Say we have a single carrier signal (not OFDM) such as 8x8 QAM. We pick ONE amplitude and phase angle from a large list of choices like these diagrams...
The output is still both amplitude and phase modulated but now with 256 possibly phase angles and amplitudes. It’s not that two phases exist. It’s just a mathematical convenience of the complex algebra involved. In OFDM we add together multiple frequencies at once. The spectrum looks nothing like QAM but again we are modulating both amplitude and phase angle but looking at it from this perspective is messy at best.

This is very different from power transmission where we never add phases except rotations in phase shifting transformers. At best OFDM is sort of related to harmonic analysis.
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I'm well aware of the details and implementation of single carrier QAM and multicarrier QAM such as OFDM in communications systems, and have participated in the design of several mixed-mode integrated circuits to implement QAM in transmitters and receivers. My point is that QAM is modulated onto a carrier for a transmitter, and also demodulated from a received QAM signal, using a pair of double-balanced mixers that are fed with local oscillator outputs that are phase shifted from each other by 90°. See the link below. The instantaneous value of the I and Q baseband signals represent the magnitude of the in-phase and quadrature components of the signal. The constellation of symbol points in the I/Q plane such as in 256 QAM that you mentioned above are the value of the of the modulated signal at the point in time that the signal is sampled. The path that the modulated signal vector takes in between these symbol points and the speed with which it moves influences the occupied bandwidth, and so appropriate baseband filtering is applied to minimize this bandwidth.
Multicarrier modulation like OFDM does not need additional RF mixers and local oscillator frequencies to implement it with today's technology, because the bandwidth of the baseband data converters and digital signal processing is adequate to do it all digitally.
By the way, I've also designed Cartesian feedback integrated circuits to linearize digitally modulated RF transmitters using a quadrature modulator in the forward path, and a quadrature demodulator in the feedback path.

My point in bringing this all up is not to say that power transmission is the same as quadrature amplitude modulation, but that 2-phase local oscillator signals at 90° are pervasive inside of the digital communication products we commonly use. I thought it might be interesting to mention that 2-phase has other applications than just in power distribution.

https://www.faststreamtech.com/products/qam-modulator-and-demodulator/
 
You haven't fully understood this subject until you read all 1259 posts in this thread. Note I got the last word. 😄

Sin(x+180deg) = sin(-x)
(only applies to ideal center-tapped single phase).

Some utilities call a 3-wire 120/208 service single-phase. That's probably the most wrong it gets on this subject, but nomenclature is nomenclature.
 
Ok... so just to add some fuel to the fire.....

If a 'device' is powered from two hots (phases?) & does not have a neutral connection.......is that device single phase?

(I vote that it is, since the device only sees one sinewave (ie. the potential difference BETWEEN the two hots))
 
AdrianWint said:
Ok... so just to add some fuel to the fire.....

If a 'device' is powered from two hots (phases?) & does not have a neutral connection.......is that device single phase?

(I vote that it is, since the device only sees one sinewave (ie. the potential difference BETWEEN the two hots))
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This is one the aspects that divide some on this.

To the load, yes there is only one 180 degree voltage wave.

To the rest of the system yes there is still voltage differential of 120 degrees between each "phase conductors" in reference to the neural point, until you complicate this with high leg delta systems where they now call one point "neutral" though it isn't technically neutral to the whole system.
 
AdrianWint said:
(I vote that it is, since the device only sees one sinewave (ie. the potential difference BETWEEN the two hots))
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This is how I was taught to count phases - ignore any neutral as it is no different than any tap on a multi voltage winding.
 
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