Why doesn't everything use high voltage power?

[Mark R]

Using a higher voltage means you can use a lower amperage. The lower the current flow, the less energy is lost to heat in a resistive substance (copper). Thus, this is why transmission lines are several tens of thousands to hundreds of thousands of volts (and kiloamps of current). Over a long stretch the savings are very, very pronounced.

Fixed.

Big power lines (in excess of 100 kV) carry currents in the thousands of Amps range. Now that's BULK. Think about it - if you need to carry the power from a big nuke station (2 x 10^9 Watts) at 500 kV - that's 4000 A (which would be divided into multiple phases). But still, that's over 1 kA per phase, for a single plant. If you've got a cluster of plants, or a multi-unit plant, then the currents can be a lot higher.

The current is so high, that the wires get too hot to touch (that's why birds don't sit on the power conductors on high voltage lines - they only sit on the safety ground wire). Typically power lines are designed to operate at wire temperatures of about 150-250 F. There are new high-tech carbon fiber cored power cables, which are designed for upgrading power lines, which can operate at 300 F (and they have lower resistance too) significantly increasing the power handling capability of the power line - although they don't do anything for the efficiency.

 

[ussfletcher]

Fixed.

Big power lines (in excess of 100 kV) carry currents in the thousands of Amps range. Now that's BULK. Think about it - if you need to carry the power from a big nuke station (2 x 10^9 Watts) at 500 kV - that's 4000 A (which would be divided into multiple phases). But still, that's over 1 kA per phase, for a single plant. If you've got a cluster of plants, or a multi-unit plant, then the currents can be a lot higher.

The current is so high, that the wires get too hot to touch (that's why birds don't sit on the power conductors on high voltage lines - they only sit on the safety ground wire). Typically power lines are designed to operate at wire temperatures of about 150-250 F. There are new high-tech carbon fiber cored power cables, which are designed for upgrading power lines, which can operate at 300 F (and they have lower resistance too) significantly increasing the power handling capability of the power line - although they don't do anything for the efficiency.

They aren't sending all of that through one line, they spread it out quite a bit.

 

[disappoint]

There are new high-tech carbon fiber cored power cables, which are designed for upgrading power lines, which can operate at 300 F (and they have lower resistance too) significantly increasing the power handling capability of the power line - although they don't do anything for the efficiency.

Given I^2*R is heat loss, how is lowering the R not going to affect efficiency? Perhaps not as much as lowering the current, but certainly, it will have some affect.

 

[Mark R]

Given I^2*R is heat loss, how is lowering the R not going to affect efficiency? Perhaps not as much as lowering the current, but certainly, it will have some affect.

The idea is that they increase the current, and accept much higher I^2.R losses (because the cables can tolerate it).

Because losses are proportional to I^2 they increase faster than the current - so the net result is that efficiency is reduced, but more power is transmitted. It comes down to cost - the power company is prepared to waste more power, if it's cheaper to waste the power than to build new towers to hold heavier cable.

 

[DrPizza]

What gets you is the overall power dissipated into you, that's why static electricity can be incredibly high voltage but harmless. The static electricity has a fixed amount of charge built up, and one that charge is gone no more current can flow. This is the same reason why high voltage tasers and capacitors aren't particularly lethal.

I think more appropriately, it's energy that dissipated; power is the rate at which it is dissipated. Also, high voltage capacitors can certainly be lethal.

AC or DC doesn't matter (lightning is DC and that kills people just fine), what matters is that the current goes across your chest (such as holding a live wire in one hand, and being grounded on the other side).

Actually DC is slightly safer than AC at the same voltage.

very true!

I can't figure out what you were trying to say in the post prior to this. People are using a certain amount of power. You, the electric company, have to provide that power. You can provide that power with a low voltage and high current, or you can provide that power with a high voltage and low current. Since over a given length of conductor, there is a fixed resistance, tis better to have a higher voltage than current, because the higher the current, the greater the energy lost to heat in the wire. That seems to be what you said "very true" to here, but seemed to dispute in the post before it.

 

[Special K]

If you treat the wire as a resistor, that V refers to voltage drop across the wire, not the voltage being sent.... So yes you could use that V, but it's not the 220V we're talking about. It's a little harder to determine that I suppose?

Ah, good point. The V does refer to the voltage dropped across the line itself, not the voltage at the source. I was digging through my transformer notes and found the following 2 equations:

Np*Ip = Ns*Is
Vp/Np = Vs/Ns

p is the primary coil, s is the secondary coil.

Basically if you want to increase the secondary voltage of the transformer (i.e. a step-up transformer, which is what we are doing to the power before we transmit it across the lines), you will decrease the current.

 

[Matthiasa]

If they really wanted to improve efficiency without affecting safety, they could upgrade from 60hz to something higher like 120hz or even higher than that. I mean just comparing 240v 50hz and 120v 60hz tends to be around the same efficiency, which should say quite a lot about how frequency affects efficiency.

Changing frequencies changes how devices operate far more then changing voltages.
The ratios would stay the same bumping up voltage assuming you don’t reach breakdown points for the parts.(for non active parts)
Changing the frequencies doesn’t do that so nicely, when your inductor starts to act like a open circuit, or your resistor starts acting like an inductor or antenna.

It would also change reflection stuff within the line though other stuff stays the same but yeah.

/hopes stuff was remembered semi correctly

 

[Gibson486]

I think more appropriately, it's energy that dissipated; power is the rate at which it is dissipated. Also, high voltage capacitors can certainly be lethal.


Actually DC is slightly safer than AC at the same voltage.


I can't figure out what you were trying to say in the post prior to this. People are using a certain amount of power. You, the electric company, have to provide that power. You can provide that power with a low voltage and high current, or you can provide that power with a high voltage and low current. Since over a given length of conductor, there is a fixed resistance, tis better to have a higher voltage than current, because the higher the current, the greater the energy lost to heat in the wire. That seems to be what you said "very true" to here, but seemed to dispute in the post before it.

DC can be safer than AC in terms of arc flash, but it is not true in terms of electrocution. It does not matter anyways, however because high power DC is reserved for few applications.

As for the latter question....

You cannot just come out and say higher voltage leads to lower current. That is incorrect. 480V over 2 100 ohms is greater than 120V over 100 ohms.

As for supplying and receiving power, yes, higher voltage will lead to lower amperage, but only because that is what the product is designed for. If a product takes 1400 watts, it will take 1400 watts. In that case, power consumption is limited to what is needed and higher voltage will lead to lower current.

In terms of supply power, the resistance of a line dictates what the maximum current will be. The way things are designed is by what load they expect. Whether it be 120V 1 phase, or 1440KV 3 phase, they all have one thing in common, there will be a voltage drop. If the line is long enough, the voltage drop will be so big that they will need to bump the wire size up to compensate.

 

[olds]

wow, how old were you? sounds a great thing to do while saying "hey guys, watch this!"

I was 20.

 

[soydios]

Misconceptions abound in this thread.

Lemme try and clear some up:
1) It is more efficient to transmit power long distances at high voltage and low current than low voltage and high current. The heat losses in an electrical line result from current conduction, not voltage, so less current results in less loss.
2) Higher voltages are more dangerous and harder to handle because they arc farther and produce more current and power when short-circuiting through material of a given resistance. A high-voltage electric motor requires much more insulation than a low-voltage one to prevent arcing.
3) Yes, it is the current that kills you if you are electrocuted, but higher voltage across a given resistance, i.e. your body, results in a higher current. No matter how hard you try, a 1.5-volt AA battery won't electrocute you because the voltage cannot produce enough current through your body. For a different reason, static electricity won't kill you either, because the current source of the accumulated charge cannot produce enough current, even at thousands of volts. Several thousand volts across your heart, though, will produce enough current to kill you. Hence the several hundred volts in household use.
4) Most electric devices operate at low voltages. An alkaline battery cell produces about 1.5 Volts. A Nickel-Metal-Hydride battery cell produces about 1.2 Volts. A lead-sulfuric-acid battery cell produces about 2.0 Volts. A lithium-ion or lithium-polymer battery cell produces about 3.7 Volts. Most chips are built to run at 5 Volts or 3.3 Volts. Extremely low voltage chips like the latest CPUs are built to run at only a little more than 1 Volt.

 

[ShawnD1]

yes, but working in the industry, I can tell you that a 10A breaker will not always trip at 10 Amps.

10A is the instant trip setting. They are supposed to begin a timed trip at 80% of this. This is why the maximum load on a 15A breaker is only 1440W (12A sustained current).

 

[AlienCraft]

Because Thomas Edison was able to persuade The Powers That Were at the time that Nicola Tesla was a wacked out Russian Freak-a-zoid, and that Edison's design for Electrical Power Distribution was the most practical.

 

[ussfletcher]

Because Thomas Edison was able to persuade The Powers That Were at the time that Nicola Tesla was a wacked out Russian Freak-a-zoid, and that Edison's design for Electrical Power Distribution was the most practical.

Totally incorrect.

Edison championed DC power, which is not effective for power transmission. For DC power to work, you utilize the forward flow of electrons (think like a garden hose) This creates a lot of excess heat and dissipates the energy very quickly (tens of miles)

Tesla and Westinghouse were involved with AC power, which works by shifting the polarity of an electric field to move electrons back and forth in essentially the same space, thus less energy lost.

All things considered, I'd say that Edison was the freak, he would electrocute animals like elephants with AC power in order to show how dangerous it is.

 

[AlienCraft]

Totally incorrect.

Edison championed DC power, which is not effective for power transmission. For DC power to work, you utilize the forward flow of electrons (think like a garden hose) This creates a lot of excess heat and dissipates the energy very quickly (tens of miles)

Tesla and Westinghouse were involved with AC power, which works by shifting the polarity of an electric field to move electrons back and forth in essentially the same space, thus less energy lost.

All things considered, I'd say that Edison was the freak, he would electrocute animals like elephants with AC power in order to show how dangerous it is.

oh. oops.

Got my stories mixed up.

<old burnt out, what can I tell you.?

 

[Mark R]

10A is the instant trip setting. They are supposed to begin a timed trip at 80&#37; of this. This is why the maximum load on a 15A breaker is only 1440W (12A sustained current).

A 10 A breaker will break 'eventually' above 10A (typically within 1 hour between 10A and 10.1 A).

The breaker will trip progressively faster as the current increases. Eg. 15 minutes at 10.5A, 1 minute at 19 A, 10 seconds at 30 A, 1.5 seconds at 60 A.

Breakers also have an 'instant' trip current. This is specified in addition to the 'current rating' of the breaker. A 'class A' breaker will trip instantly (0.01 seconds) if the current reaches 3x the rated current (30 A in this case). Most breakers are 'class B' which trip instantly at 5x the rated current (50 A in this case). 'Class C' breakers are available for special use (e.g. for industrial machinery with big motors, or heavy HVAC) which will not trip instantly until 7-10x the rated current.

However, it is strongly recommended that you not operate breakers above 80% of their rated current, because under high temperature conditions, breakers increase in sensitivity. E.g. at 50 C a breaker may begin to triggering at 80% of rated current. (Don't forget that breakers produce heat too - so on a hot day, a closed panel can reach significant temperatures).

 

[GodlessAstronomer]

All outlets are 240v here.

 

[Jeff7]

All outlets are 240v here.

Psh, yeah. New Zealand volts.

USA volts are so much better - they can make a REAL man out of you. "He who shall not be named" surely uses USA volts in his appliances, and you can see how awesome it's made him. :awe:

 

[GodlessAstronomer]

Psh, yeah. New Zealand volts.

USA volts are so much better - they can make a REAL man out of you. "He who shall not be named" surely uses USA volts in his appliances, and you can see how awesome it's made him. :awe:

You're right, with the current voltage exchange rates it hardly seems worth it to plug in my laptop these days. Damn voltconomy.

 

[WHAMPOM]

The higher the voltage, the more efficient the power transmission, right? So why doesn't everything use high voltage power?

Yes, I know I'm retarded for asking, but someone please take the time to answer in between guffaws! :awe:

What??? Do you mean 220 or three phase 'cause every high line out there is high voltage until it gets to your transformer where it get reduced to home voltage.

 

[Engineer]

I've been shocked by 110v at least a dozen times. I never died any of those times.
I've been shocked by 220 once and I didn't die then, either.

I have been shocked by 480V twice and it felt like I died both times! D:

 

[Gibson486]

I have been shocked by 480V twice and it felt like I died both times! D:

3rd times a charm