Understand Power Loss in a Wire Through V, I and R

[kuwerty]

I would be grateful if anyone could clear up my confusion with this relatively simple concept. It has been bugging me for 3 years now and I've never had a clear answer from my teachers.

Consider a power line transmitting electricity:
Power loss in the wire = I²R = VI
To reduce power loss I am told you are to reduce the current...

However when you reduce the current (say 10x) you must increase the voltage 10x.


I = V/R therefore Power can also be written as V²/R
If you are increasing the voltage Power loss is anything but decreased?

 

[berkeman]

I would be grateful if anyone could clear up my confusion with this relatively simple concept. It has been bugging me for 3 years now and I've never had a clear answer from my teachers.

Consider a power line transmitting electricity:
Power loss in the wire = I²R = VI
To reduce power loss I am told you are to reduce the current...

However when you reduce the current (say 10x) you must increase the voltage 10x.


I = V/R therefore Power can also be written as V²/R
If you are increasing the voltage Power loss is anything but decreased?

The power lost in the line is VI where the V is the voltage DROP across the wire, not the total AC voltage that is being transmitted down the line. The voltage that you get at the end is Vin - Vdrop, so the losses are Vdrop * I, or just I^2 * R.

 

[zgozvrm]

To reduce power loss I am told you are to reduce the current...

Basically, the concept you're missing is that the same power can be delivered at higher voltages, at lower amperes.

Electricity is delivered through wires at a higher voltage than necessary for a couple of reasons:
- Since the power remains the same, more volts means less amps. High amps requires larger wires than low amps. Smaller wire costs less and weighs less, so supports don't have to be so bulky which, in turn, saves on material thus saving even more money.

- Without going into great detail, low amperage transmits more "easily" than high amperage. Think of a small water pipe. It can deliver water efficiently up to a certain point. Once the flow (compare to amps in a wire) reaches a high enough level, friction loss begins to make a more noticeable effect (think voltage drop). This "friction" accounts for some loss in power, therefore running electricity at a higher voltage reduces that effect.