50 hz VS 60 hz and a 120 HZ question

Thanks to everyone for clearing this up for me. Thanks Karl

"john" wrote: There are many things to consider including idling at a stoplight with a gas engine while with a electric motor it is not using any electric. Also a motor can be a braking device and put power back into the batteries. No oil is needed for lubrication of the motor other than an ocasional shot of grease. (clip) ^^^^^^^^^^^^^^^ John, I am well aware of the advantages of electric and hybrid cars. I am trying to get a handle on HOW MUCH advantage they offer in terms opf air pollution. An electric car is not totally non-polluting. The electricity to run it comes from a power plant somewhere, connected the power grid. We know how much CO2 is released when a pound of fuel is burned. The comparison that needs to be made is, how much fuel does it take to run an automotive engine, vs how much does it take in a power plant to drive it the same distance? Some of the power fed into the grid is wasted as heat. How much?

Roughly half.

According to Jon Elson :

Hmm ... the universal motors would probably still work reasonable well -- mixers, hand-held electric drills, toolpost grinders and the like. But most induction motors would have to be replaced, or at least the start capacitance value changed (e.g. in single-phase lathes and the like), or the run capacitance values (in things like my air conditioning compressor and the associated fan, both of which use phase-shift capacitors -- to run what I think are actually three phase motors from single phase power.

For that matter (assuming that we are only talking about 120 Hz, not 400 Hz) -- four-pole three-phase motors running lathes and milling machines would probably handle the switch with only an increased speed as a result, though two-pole ones might risk centrifugal disassembly of the rotor. :-) For those which could handle the switch, we would probably have to change pulleys to keep the speeds reasonable -- or to hang a VFD between each motor and the new higher-frequency three phase, which would at least isolate the motors from the frequency change.

I'm glad that you covered the question about insulation -- it saves me the trouble, and makes me glad that I read the followups. :-)

As for the transmission lines, I notice that the high-tension three phase lines every few towers appear to interchange two of the three wires -- I guess making the equivalent of twisted pair wiring to minimize radiation by canceling from the other phase. I suspect that the interchanges would have to be redone to be closer together at a higher frequency.

Enjoy, DoN.

Once the air is ionized DC or AC will substain an arc. An inductive load on a DC circuit will cause arcing but a resistive load will be a lot less. Any high voltage device is costly... especially 3 Ø.

John

3-phase motors have another important feature - they always start in the right rotation IF the power company doesn't make changes and screw up the phase rotation at their end - and they're well aware of the need to not do that. Important for running elevator pumps and various lifts and hoists and machine tools...

The cost of a 3-phase breaker panel is only higher than 1-phase because of the increased materials costs - they have to have a more complicated to manufacture bussing system, a 1-Phase buss can be stamped and formed automatically.

And they don't sell as many of the panels, so the incremental manufacturing costs are higher. They can't just leave a production line cranking them out three shifts a day.

You only need 3-pole breakers on the 3-phase circuits - single phase loads would continue to get the same 1-pole and 2-pole breakers they always have.

It is no big problem to make a "split buss" panel for residential, it has been done in the past. The meter socket and Main Breaker were

3-phase, but the third 'C' phase only went to the first buss plug-in location to accommodate one or two 3-phase load breakers - the air conditioning and a "load to be named later". C-B-A-B-A-B-A-B...

If the house is fed with an 120V/240V Open Delta "High Leg" 3-phase system you don't /want/ the whole panel to be 3-phase. The High Leg is (208V?) to ground and any loads accidentally connected to it by the DIY homeowner will tend to "go splodey" in a spectacular manner.

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Don sez:

"As for the transmission lines, I notice that the high-tension three phase lines every few towers appear to interchange two of the three wires -- I guess making the equivalent of twisted pair wiring to minimize radiation by canceling from the other phase. I suspect that the interchanges would have to be redone to be closer together at a higher frequency."

Power lines interchanging location among themselves are part of a "transposition" scheme. All open wiring, be it power or communications, employs some sort of transposition. Open wire pairs with high frequency "carriers" are transposed at regular intervals in a scheme (crosstalk elimination) that protects them against other wire pairs on the same pole line, and protects other wire pairs from the carrier (s). The transposition scheme on a large open wire lead can be quite complex. It is closely related to common mode rejection of audio disturbances on balanced lines or the inputs of operational amplifiers.

A more apparent transposition is that found in communications cables. All the pairs are twisted at varying pitches throughout the cable and the locations of individual pairs is moved around within any individual group, or bundle, of wires within the cable. Bundles are twisted around each other.

Bob Swinney

"transposition" scheme. All open

Open wire pairs with

(crosstalk elimination)

other wire pairs

be quite complex. It

lines or the inputs of

pairs are twisted at

moved around within

twisted around each other.

In this instance, it's to equalise inter-phase and phase-earth capacitance and also phase inductance. Doesn't need to be done very often at all, but does need to be done once in a while.

Mark Rand RTFM

Are they getting lower transmission losses by eliminating the 'skin' effect of AC?

Wes