Why do powerlines usually come in groups of three?
It is called three-phase electric power. Think of alternating current as waves in water. For each cycle, you start with the wave at the neutral position (no current flowing). The wave moves up to the maximum height and then down to the neutral position again. Then down to the lowest point, and back up to neutral, to complete the cycle.
In a three phase system, the alternating current in the wires are out of sync, so that when one wire is at the neutral position, the other two are not. This provides continuous power for large motors. It also allows the production of a rotating magnetic field, which gives you a very powerful motor.
The three phase system also lets power companies send more power with less material in the conductor. That saves on copper, and means less weight for the wires to support.
three phase electric power
We have read your answer but still have questions. :-)Lots of complicated stuff to explain in one photo caption.
I think we understand the need for 3 to provide continuous current. If you didn't have 3, it would "flicker" right? But where exactly is the "3"? Are you talking about wires? If wires, we see 6. Is each set of wires considered a "set"? Thus making the 3? In these sets, one is a "go" and one is a "come"?
What are the two higher wires that are barely visible? Do they carry current? Or do they serve just as airplane catchers. Just kidding.
The Andrews
Re: three phase electric power
Great questions. Your house probably only uses one phase, and yes it does flicker, although too fast for your eyes to detect. High power lines are usually in threes (in the case of this photo, two sets of three). There are two wires for each phase here, because the lines are carrying a LOT of power. Instead of making two entire sets of towers, it is easier to use more wires. Why not use one big wire? Because bigger wires are heavier, and the wire has to support its own weight without breaking.
The two higher wires are grounded, and serve as lightning protection. A lightning strike will usually (but not always) hit the upper wire, instead of blasting the powerlines.
I hope this helps.
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