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Thanks for the kind words - I'm glad you enjoyed the site. : Yes. However, the extra insulator segments are not really overkill, they are there to provide sufficient margin to prevent flashovers, nuisance tripping of circuit breakers, and potential service disruptions. Additional design margin is needed to prevent flashovers from relatively common situations such as overvoltage transients (circuit switching or lightning) or via suspension insulator segments that become leaky or defective (through physical damage, dirt, condensation, corona damage/tracking, or previous flashovers), Yes - your transmission lines are likely either 115 kV or 138 kV. In the US, some commonly used AC power "transmission" voltages are 69 kV, 115 kV, 138 kV, and 240 kV, while long haul bulk power transmission lines operate at 345kV, 500 kV, and 765 kV. "Distribution" voltages are lower - typically 33 kV and below. Older systems may run as low as 2.4 kV, but more commonly used voltages include 4.8 kV, 7.2 kV, 14.4 kV, 24 kV, 33 kV, and 69 kV. Thanks! Small devices like this are typically cutout switches or instrument/control transformers. However, if the devices ONLY have two terminals, they may be inductors. Unfortunately, I haven't seen these in power lines in our area so I can only speculate. Since they may be physically small and are connected in series with the 3-phase circuits, they are likely inductors. Lumped inductance is sometimes added in series to block high frequency signals (such as RF control/monitoring signals that are often used by utilities), but these are most often air core coils. Small inductors are also used to "slow down" high speed transients. These are used along with arresters for lightning and transient overvoltage protection. Also, inductive reactors are sometimes added in series to reduce the available fault current during a short circuit. Another possibility is that these are inductive voltage regulators - these can be bridged across by the parallel shorting switches to remove them from service. It's really hard to tell without seeing what they actually look like...
: Awesome website, Bert! Although I don't have a Tesla coil, I've always been
: interested in electricity and high voltage. Have played with NSTs, Model-T
: coils, Van deGraaf generators and other fun stuff. Love your Arcs &
: Sparks page, too.
: 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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