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About ten years ago I moved to a new area, and my house is only about two miles from what appears to be a pretty major regional power distribution station. A set of lines (six wires, two circuits) comes in from the hinterlands and splits into branches that feed substations farther down the line. Some interesting hardware behind those fences. I've been curious to know just what voltage they're handling on those lines. Can you tell, at least roughly, the voltage carried by the lines from the type of insulators that hold them? I saw a show on the History Channel the other day about linemen who use helicopters to service energized lines, and they mentioned that the 345 KV line they were working on used insulators with 18 "bells." They said two of those were overkill, and that 16 would be the bare minimum to withstand the voltage. Since the feeder lines I see have insulators with 8 bells, and assuming the rule is to have 2 extras, then that would make the proportional voltage for those lines about 130 KV. Does that make sense? What are the common voltages used to distribute power? I see (on wooden poles) lines held with insulators that look like a single knob (these directly feed transformers that feed homes and businesses), others that stand about 6" tall (one line of these seems to feed a substation a few miles from the secondary distribution station near my home). I also see poles with insulators over a foot long (I'd guess a good 18"), set quite high. These also feed substations. I could go on and on with questions here. How about this one: What are the devices that look like transformers, with two high voltage terminals on them, that connect one power wire to another (same phase)? They are inserted in series with the circuit, sometimes manual knife switches are mounted in parallel with them (which always seem to be in the open position). Some of these are BIG, some are the size of smallish coffee cans, but none of them appear to have primary and secondary wires, just the two terminals. No control wires, either. I assume the physical size is related to their KVA ratings. They are almost always installed in sets of three to serve all three lines of the circuit. Could they be transformers? If so, for what? They insulators on each side of them are the same size. That's enough for now! Thanks, Bert, for having this very cool page.
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