Wiring question

That doesn't change phase. But now that I think of it, they do make phase converters using a motor and a generator.

"DJ Delorie" wrote: (clip) My primary motivation, other than to have some fun on a Friday, is to keep people from confusing single-phase house current with the original two-phase (4 wire, 90 degrees) AC invented by Tesla. This

If you look at two voltages on an oscilloscope, and see one reaching its positive peak while the other is reaching its negative peak, is one 180 degrees out of phase with the other? According to your thinking, it depends on the source. If its coming from a center-tapped transformer, it's not a phase difference, but a polarity reversal. If it's coming from generator windings that are positioned on opposite sides of the stator, it would be a 180 degree phase difference.

Suppose its coming out of a black box?

DJ Delorie wrote in news: snipped-for-privacy@delorie.com:

In true Usenet-Wreck-ElectricityThread fashion! :)

Since you said "positive peak" and "negative peak", no. Had you said "most positive" and "least positive", yes.

I think the answer depends more on stuff other than the signals themselves. If you measure between the signals, and the result isn't the simple subtraction of the two signals, it's a phase difference.

What if you had a 120VAC signal, and a 12VAC signal of opposite polarity? Are they out of phase? What about 120VAC and a -12VAC signal of opposite polarity (the signs cancel and you get the "same" polarity)? Good thing it doesn't matter in practice. Of course, if it *did* matter in practice, it would be because of a measurable difference, and then the answer would be obvious ;-)

My scope has an "invert" switch that further confuses the issue.

Then it doesn't matter. Usually it's a matter of definition, not evidence. On the schematic, the signals would be labelled relative to the circuit's common ground, and as to whether they were defined by voltage or phase. It matters a lot more when the shape of the signal is asymmetric (like a pulse or ramp). An inverted pulse is *way* different from an out of phase pulse.

In the case of house current, since we *do* use the 240VAC voltage offering, the definition is one of voltage, not phase. You use all of the voltage, or half of it. If you had three phase power, you couldn't add the three voltages up to get a single 3x voltage, so the definition is one of phase. You normally have three phase power because you're taking advantage of the phase differences, not the range of voltages you get.

"Yes"

| ====>I would still like to know if the cat in the black box is | alive or dead? *TIC*

"No"

"Leif Thorvaldson" wrote: I would still like to know if the cat in the black box is alive or dead? ^^^^^^^^^^^^^^^^ Unless you know of a third possibility.

This is what the blink tag is for:

Schroedinger's cat is not dead!

No there isn't. It's *been*done*. many times, many ways. google for "quatrature amplitude modulation", for a _relatively_ easy-to-understand example.

============================== Technically true, but in practice, a wye primary can be used with a delta secondary allowing, when rectified, a 12 pulse output rather than the 6 pulse of either the dellta/delta or wye/wye. This feature is used in X-ray generators to achieve near DC levels at the X-ray tube.

Ken Moon Webberville, TX.

Ken

I don't doubt that X-ray machines have special transformers in them for their needs. But for distribution transformers a wye primary and a delta secondary is very common, as is a delta primary and a wye secondary. The determining factor on whether the primary is going to be wye or delta is the actual line voltage and the nameplate rating on the transformer. For example, we have a 12KV 3 wire primary that is 12KV phase to phase and

The determining factor on whether the secondary is going to be delta or wye is the voltage that you want to serve. If you are going to serve a

Note: to serve a 120/208V service we must pull the lids off the transformers and parallel the secondary coils inside.

So by stocking 12KV 120/240V transformers we can use these in both primary systems and serve 120/240V 3 phase, and 120/208V 3 phase and

Next week we'll be covering VARS (volt amps reactive) captive reactance and inductive reactance, circulating current, fault current, third harmonic overvoltage, and ferro-resonance. :)

Don