Voltage around the world...

[Heliostat]

I have a sharply limited understanding about the technical details of electricity. I can't tell amps, volts, watts, etc. apart.

What's the advantage of using 230/240 volts instead of 110/120? North America uses the lower voltage, whereas most of the rest of the world uses the higher amount. Is there some significant difference between the two configurations, or is it just out of tradition?

 

[Corny]

A higher supply voltage decreases the amperage in the circuit. You can use cheaper, thinner wires with lower voltages, and you have less "leakage" when transporting the current over longer distances. So if you either have bad power grid or need to transport current through long overland distances a lower voltage might be preferrable.

 

[thermodynamics]

It's simply a difference in what we started with here in North America. Once a voltage is standardized at everyone uses it, it's really hard to change.

120 certainly works fine. We have the same high voltage transmission lines that are in the rest of the world. The difference is that the step down at the very end is lower.

Actually, here in the US at least, we have something called "split phase" for residential and light commercial use. It's a way of getting both 120 and 240 from the same power lines. In split phase, the two legs from the power company are 180deg out of phase with each other, so if you connect between the two line legs, you get 240. If you connect between ground (called "neutral" in this case) and one of the legs you get 120.

And to make things more complex, we also have 208V 3 phase, but that's usually only found in commercial buildings that have lots of motors.

 

[Corny]

Oh we have three phase alternating current here, too. 400V, 120° out of phase to each other. multiply with √ 3 = ~231 V for each phase.

 

[trawler69]

A higher supply voltage decreases the amperage in the circuit. You can use cheaper, thinner wires with lower voltages, and you have less "leakage" when transporting the current over longer distances. So if you either have bad power grid or need to transport current through long overland distances a lower voltage might be preferrable.

Actually going long distances you need a higher voltage to reduce the current and therefore the voltage drop and power loss so you use cheaper thinner wires with high rather than low voltages As power loss = Amps ^2 x Resistance and, keeping the wire size the same, doubling the voltage halves the current and reduces the power loss by a factor of 4.

While 110 volts is safer as you will never get much of a shock from it you do need thicker cables to carry the same power as the current is doubled. All power is generated and transmitted as 3 phase, it is only split into single phases out side the property or at the end of the street. Often houses next door to each other will be on different phases and so you could have over 415 volts between the lives (hot) of next door houses in the uk. 415 = 240 x sqrt 3. (Actually in the uk the "official voltage" is now 230, in fact it is almost always over 240 but it gives them leeway to drop it without penalty in the case of over demand) The split phase in the US is a way of getting a higher voltage for equipment that uses high power so wire sizes and currents can be kept low. Often fuse boards have two sides each side is 180 degrees out of phase with the other with 110v ccts being taken from centre tap to either side and high power being take from across the phases.

Yes I do work with electricity

 

[HenryReardon]

While 110 volts is safer as you will never get much of a shock from it you do need thicker cables to carry the same power as the current is doubled. All power is generated and transmitted as 3 phase, it is only split into single phases out side the property or at the end of the street. Often houses next door to each other will be on different phases and so you could have over 415 volts between the lives (hot) of next door houses in the uk. 415 = 240 x sqrt 3. (Actually in the uk the "official voltage" is now 230, in fact it is almost always over 240 but it gives them leeway to drop it without penalty in the case of over demand) The split phase in the US is a way of getting a higher voltage for equipment that uses high power so wire sizes and currents can be kept low. Often fuse boards have two sides each side is 180 degrees out of phase with the other with 110v ccts being taken from centre tap to either side and high power being take from across the phases.

Yes I do work with electricity

Many years ago, the father of my best friend was an electrician. He explained 3-phase this way.

Electric motors are kept spinning by a pulse of electricity. Every pulse keeps them going, but there is an almost imperceptible lag in the speed of rotation between each pulse.

When a motor runs on two phase, it receives a separate pulse from each phase.

When a motor runs on three phase, it get three pulses in very nearly the same amount of time - which makes the motor run more efficiently.

As he explained it, this was important for very large motors.

Hope I remember it correctly - it was a long time ago.

 

[trawler69]

Not a bad analogy. I look at it from the generator as a magnet passing 3 coils of wire in a revolution generating voltage in each one as it passes. In the motor the 3 coils generate a moving magnetic field that a piece of iron follows round. Somewhat simplistic but is effectively true. In a single phase induction motor a "starting system" is used to artificially create a rotating field, usually a capacitor and a second coil which creates a second phase 90 degrees from the primary phase. Once the motor is spinning this can be switched out as the momentum of the armature will keep it rotating in the same direction. If you power up a single phase induction motor without its starting circuit it will sit there and hum without turning until you manually give it a flick, it will then continue to rotate in whatever direction you flicked it. To reverse a 3 phase motor you simply swap 2 of the phases over so that the magnetic field appears to rotate in the opposite direction.

I am such a geek

 

[Heliostat]

You guys went a little over my head, but I think I got it now. So, tradition, efficiency, and capability for higher voltage (in the 240v countries) for big electric elevator (& such) motors. Thanks!

 

[trawler69]

Makes sense...

Now, One thing i'm not clear on however is how one can calibrate a quantum torpedo to pass through a ships sheilding system based on it's phase varience.... Perhaps you could enlighten us on this topic

The clever thing about the ships shielding system is that its absolute elevation varies in proportion to the phase of the moon and the time of day. The knack is to get the torpedo to deliver its quantum by calibration of the trajectorially coincident points. By careful adjustment of azimuth whilst taking into account inebriotically induced fluctuations of verticality. On successful completion it is advisable to asprinate the area whilst retreating under cover of quiltness until the concomitant throbbing subsides.