A lesson in voltage and amperage, please

[Perplexed]

I did, just not explicitly. I mentioned the equal and opposite rotating magnetic fields of single phase requiring special starting means to lock the rotor with one of the fields vs the singular rotating magnetic field of a 3 phase, and all of that was off topic, really, to the OP's question. But the OP seems to be broadly curious about most aspects of electricity, so hopefully he did not mind.

I don't mind at all! I appreciate all the input. I've learned quite a few things about electricity in this thread - as well as being dazed and confused about other things

 

[Matt_Jr]

I don't mind at all! I appreciate all the input. I've learned quite a few things about electricity in this thread - as well as being dazed and confused about other things

I know just enough to really confuse me... hmmm.... is that good or bad ?

 

[TRR]

One other thing I haven't seen mentioned is that household 120v circuits normally have a breaker of either 15 amps or 20 amps. So the most power you're going to be able to get is 120v * 20a = 2400 watts. (Yes I know there is a 30 amp breaker at HomeDepot, but normally it's 15 or 20 and more likely 15 amp breaker.) So to get more power, one has to go to 240volts and (I think) the most you can get from a plug is 50 amps before you have to hardwire the machine to the wall. Has anyone seen a plug for more than 50 amps?

 

[crazyal]

Yes there are plugs that can handle more than 50 amps but they are not found in the home. I use some at work that can handle several hundred amps.

 

[Transit]

We are getting in deep here. We are talking about a formal AC engineering power course. Not something to be explained here to a budding novice.

As for power transmission at 1 kHz in a transformer, you are overlooking other SYSTEM losses in the overhead cross country lines and power station generators. Overall concept, as line frequency goes down, 60, 50, 25 Hz, so does the losses.

As for 3 phase power, it may be split into 3 120 volt circuits or 3 two phase 240/120 circuits.

Watts [volts x amps, real power] is power that dose something useful, it heats, moves something, makes a sound. But with machinery that has IRON in it, motors, transformers, generators, you buy, volt-amps [apparent power] from the power company because that is what they MUST generate and the part that you get to use to do something useful is WATTS. The part that is missing may be likened to be an effect factor.
Now all the talk about motors and phases are adaptations of these basics, case by case. Again we are talking engineering school, break out the slide rules and brush up on your trig.

 

[BobRip]

The devices needed to start single phase motors (capacitors, extra windings, relays and starting switches) tend to be fairly unreliable. Hence the three phase motors are much more reliable and longer life. Also the smoother rotational torque helps with mechanical reliability. When you have a million dollar machine down for a $10 capacitor you appreciate the advantages of three phase.

 

[638]

One thing that hasn't been mentioned, a 3 phase motor can be reversed by changing any two of the three input wires.

 

[Redneck in training]

In Europe has three phase power is standard. It has something to do with population density. The power consumption as well as number of users per area of the land is quite high. In other words to deliver the power is more effective using three phases while the cost is spread over many users.
Each phase is 220V against Neutral or 380V phase against another phase.
Motors can be wired either 3 X 220 (Y) for softer start or 3 X 380 (delta) for more power.

 

[Mace Canute]

But with machinery that has IRON in it, motors, transformers, generators, you buy, volt-amps [apparent power] from the power company because that is what they MUST generate and the part that you get to use to do something useful is WATTS.

Not quite correct. As far as purchasing power, it all depends on how the customer is metered. AFAIK, ALL residential meters are WATT meters. Commercial/industrial meters can be either, depending on the policies of the electrical utility.

 

[BobRip]

Not quite correct. As far as purchasing power, it all depends on how the customer is metered. AFAIK, ALL residential meters are WATT meters. Commercial/industrial meters can be either, depending on the policies of the electrical utility.

That is my understanding.