Why We Use High Voltage In Power Lines & some effects of it

High voltage power lines buzz and crackle with energy (You can hear it extra well while it’s foggy) and just like a tesla coil with a high voltage on it these power lines bleed energy into the air to ground. Moreover you can measure this. You can even hear it.


Materials:
Long thin fluorescent light bulb, multimeter, head phones, 2-3 foot (.5 to 1 meter) length of wire, High voltage AC power lines overhead.


Experimental steps:

 

  1. First off you need to find some high voltage AC (Alternating Current) power lines and position yourself under them. You will need the long haul transmission lines not the lower voltage ones that you typically see in neighborhoods. The correct ones will be high off the ground and usually have about 400Kv on the lines but can vary anywhere between 150Kv and 765Kv. The effects are much more obvious the higher the voltage.

  2. Even though I did this last in the video the easiest experiment to do is the one with the headphones. Take a set of headphones (cheaper ones actually work better because they aren’t shielded) and put them on. Then hold the plug end up above your head in the air. If you are in the US you should hear a hum matching 60Hz (oscillating 60 times a second) in most of europe the hum is at 50Hz but is still easy to hear.
  3. Next easiest is the experiment involving a fluorescent light bulb. This is only possible to see at night and works best if you let your eyes become dark adapted (hang out in the dark for longer than 10 minutes). Simply take a fluorescent light bulb (long thin ones work better) and hold it at one end pointing at the power lines. The excess energy from the power lines will flow down through the bulb and then ground out through you in the process the white powder on the inside of the tube will light up a bit. This effect isn’t the same as the higher voltage needed to excite the mercury vapor in the bulb like normal operation because the power (volts per unit time) is too low. If the power lines are not very high voltage you may be able to get a reaction by touching a length of wire to the top end, being careful not touch the top of the bulb at the same time to allow the bulb to reach to a slightly higher potential energy closer to the wire.

    WARNING: do not get too close, the specific distance varies depending on the voltage, but if you place anything close enough to the wires that the potential difference is greater than the breakdown voltage you will create a lightening bolt from the wires from the wire to ground through you. Most likely killing you. So…be safe.
  4. Next if you have access to a multimeter you can actually measure the voltages near the ground. Again it is easier to do this if you attach one end of the multimeter to a length of wire and hold this up above your head. The other end of the multimeter should not touch the ground since the conductors will make the whole multimeter the same voltage as the ground and may zero out your measurement (at least that’s what happened with me). Also be sure to use the AC detection option on your multimeter since it’s AC current in the wires anyhow. DC may show something but it will wobble about and you won’t get a clean reading. Also if you do not have autoranging on your multimeter you may have to change the range as I did.
  5. Next turn the multimeter to milliamps setting to measure the current. You should see that the amount of current is only barely detectable if at all. Even if you measured a relatively high voltage. That’s because the resistance is very high in the air.
  6. Lastly if your multimeter happens to have a frequency option (only some do) you can set it to that setting and measure directly the tone you heard at the beginning of the experiment.

If you have to do this during the day (say with a class) step 3 may be done by building a viewing box with a fluorescent light bulb inside it. Attach wires to the electrodes and extend these out the top and bottom of the box. In the side of the box cut a viewing window allowing you to look into the box and see the light.

Math:
While these are very fun experiments the fact that so much energy bleeds off from the use of high voltage one may ask why we use High voltage in the first place, and the reason is math. Loosely speaking the power companies have this problem to deal with.

 

P generated = P delivered - P loss

Since the power delivered to the end user is fixed by demand the goal is to make the losses, from resistance, as small as possible. So we need to look at how power can be represented by voltage (V), current (I) and resistance (R).

P = VI = I^2R

Substituting some of these in we can write the power delivered as Voltage times the current and we can write the power dissipated in the resistance of the wires as current squared times the resistance.

P = VI - I^2R

Now the current value is the same for both parts of the equation. Since the losses from resistance depend on the current squared if we can reduce the total current by half the losses get reduced to one quarter their previous value. However, if the power companies want to reduce the current they still have to keep the power delivered the same. So to reduce the current as much as possible while still keeping the same power delivered they have to increase the voltage by the same amount we decrease the current. In short more of the power generated gets to the end user if we make the voltage on the wires as high as possible while still remaining below the breakdown voltage of the insulation.

 

Wrap up:
This set of experiments is really fun and easy to do. We see power lines all over the place but the effects and costs of transmitting power this way are seldom discussed. Usually we are told about power generation and then taught about the AC current in the walls of the house with little or no mention of the power lines themselves. These experiments also provide a jumping off point for discussing losses in power delivery and the active inquiry into using DC instead of AC or moving our grid to a more distributed design rather than the power generation hubs we have today.

 

Linkography:

https://www.youtube.com/watch?v=aw6KfXMCZEs

http://www.bsharp.org/physics/transmission

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=941.0

https://www.youtube.com/watch?v=0D50Dcvzkr4

http://www.ucsusa.org/clean-energy/how-electricity-grid-works#.V2bTWpMrKRs

https://en.wikipedia.org/wiki/National_Grid_(Great_Britain)

 

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s