Re:Continuing frequency deviation in the Continental Europea...
by amluto on Wednesday March 07, 2018 @12:52PM
(#16538230)
Having thought about this before, here's how I think it works. The relevant effect isn't the speed of light per se -- it's the phase velocity v of 60 Hz AC power transmission, which is indeed reasonably close to c. If you have a power line of length l running East to West and the phase on the Western end lags by 2pil/v, then an electromagnetic calculation will show that power is moving Westward [1]. If the western phase leads, then power flows Eastward. If the phase is the same everywhere, then no current or power flows.
This is actually quite handy. When demand locally exceeds supply, the phase will lag (this is how generators work), and power will flow toward the excess demand.
More advanced grid operators use various devices to intentionally shift the phase to control the flow of power. [2]
[1] Actually calculating this is surprisingly complicated. You can integrate the Poynting vector; you can model the inductance and capacitance of the line, calculate the current, and use P=I*V; or you can probably do it in several other ways. You might even be able to model it as little packets of energy moving along at the group velocity.
[2] This ability is important for economic and engineering reasons. Imagine you connect two cities with two parallel, competing transmission lines. One has 100 MVA capacity, and one has 10 MVA capacity, but they have the same impedance. (This is a bit farfetched, but capacity is related to impedance, heat dissipation ability, and the ratings of whatever equipment is at the ends of the lines.) Without some kind of active control, to much power will flow through the 10 MVA line and it will fail.
This is actually quite handy. When demand locally exceeds supply, the phase will lag (this is how generators work), and power will flow toward the excess demand.
More advanced grid operators use various devices to intentionally shift the phase to control the flow of power. [2]
[1] Actually calculating this is surprisingly complicated. You can integrate the Poynting vector; you can model the inductance and capacitance of the line, calculate the current, and use P=I*V; or you can probably do it in several other ways. You might even be able to model it as little packets of energy moving along at the group velocity.
[2] This ability is important for economic and engineering reasons. Imagine you connect two cities with two parallel, competing transmission lines. One has 100 MVA capacity, and one has 10 MVA capacity, but they have the same impedance. (This is a bit farfetched, but capacity is related to impedance, heat dissipation ability, and the ratings of whatever equipment is at the ends of the lines.) Without some kind of active control, to much power will flow through the 10 MVA line and it will fail.