Power line overload

How do the 3 trip line fuses work? Can lightening hit a line and cause a surge by itself? My question is really......What does 3 trip protection offer? Is that so that just a lightening strike will not blow the fuse? Is the line given 3 tries to be sure there is a fault like a tree on the lines or a downed line?

How does the fuse keep count?

Reply to
Terry
Loading thread data ...

I think you mean reclosers, not fuses. Fuses do not count anything. They blow. Reclosers can open and close multiple times. Has little or nothing to do with outages and everything to do with the fact that 70 to 80 percent of faults on overhead lines are temporary.

Charles Perry P.E.

Reply to
Charles Perry

They aren't really fuses, they are electronic or electromechanical devices that count the number of times that the upstream reclosing circuit breaker trips. After the requisite number of cycles (current dropping to zero) within some time period occurs, they drop open. They open on a dead circuit rather than interrupting a fault as a fuse would.

What lightning really does is to create an ionized path between a conductor and ground through which the power supply voltage itself can continue to flow as a fault.

just a lightening strike will not blow the fuse?

Lighting strike or other momentary faults are cleared and reclosed by allowing the upstream breaker one quick trip to save lateral fuses. If a persistent fault occurs on a branch circuit downstream of a actual fuse, the subsequent breaker operations are slower, giving the fuse a chance to blow. If that doesn't clear the fault, the sectionalizer will cut the circuit in half after the third trip. If the fault was beyond the sectionalizer, the breaker can close and energize the good half of the circuit.

or a downed line?

With something like an electromechanical ratcheting mechanism in the old days. Electronically in modern units.

Reply to
Paul Hovnanian P.E.

|> Is the line given 3 tries to be sure there is a fault like a tree on the lines or a downed line? |> |> How does the fuse keep count? | | With something like an electromechanical ratcheting mechanism in the old | days. Electronically in modern units.

How would those be reset? Suppose there were, hours or days apart, more than one lightning induced temporary fault that only needed one open cycle to clear? Would they gradually add up? Or is there some means to manually reset if it didn't lock out at 3 so it won't add up? Or is it not worth the trouble and just take the 3rd lightning hit on the chin?

Reply to
phil-news-nospam

Forget lightning. Think any temporary fault. And yes, the old reclosers reset after a certain amount of time. They were hydraulically controlled. There were hydraulic timing circuits. You changed orafices to get different timing and number of operations to lockout. If I remember correctly, the reset time was preset. Keep in mind all of these times were somewhat variable since they depended on the viscosity of the oil.

Charles Perry P.E.

Reply to
Charles Perry

|> |> Is the line given 3 tries to be sure there is a fault like a tree on |> the lines or a downed line? |> |>

|> |> How does the fuse keep count? |> | |> | With something like an electromechanical ratcheting mechanism in the old |> | days. Electronically in modern units. |>

|> How would those be reset? Suppose there were, hours or days apart, |> more than one lightning induced temporary fault that only needed one |> open cycle to clear? Would they gradually add up? Or is there some |> means to manually reset if it didn't lock out at 3 so it won't add up? |> Or is it not worth the trouble and just take the 3rd lightning hit on |> the chin? |>

| | Forget lightning. Think any temporary fault. And yes, the old reclosers | reset after a certain amount of time. They were hydraulically controlled. | There were hydraulic timing circuits. You changed orafices to get different | timing and number of operations to lockout. If I remember correctly, the | reset time was preset. Keep in mind all of these times were somewhat | variable since they depended on the viscosity of the oil.

If you had cases where the accurate timing was critical, you'd have other major issues to worry about than the precision of the recloser resets.

Reply to
phil-news-nospam

I think the basic idea is to open the circuit long enough to allow the arc (fault) a chance to extinguish itself without a chance for re-establishing a conductive path to ground or an adjacent conductor.

When I was a kid growing up in Illinois (a location with lots of big ass lightning storms), I always thought it interesting that we could predict the next lengthy blackout would be a long one if the lights at home flashed 3 times in succession. The reclosers were utilized with sectionalizers that I believe would count the different OFF intervals and drop out an isolated section of the line after 1, 2 or 3 openings of the circuit. Thus, you might loose part of a neighborhood, but the whole side of the town would still have power.

Apparently faults can be anything from trees falling on the lines to exploding transformers or sometimes when the winds picked up, the lines would swing into each other and start arcing which was really scary if you were just driving around.

One thing that I think has changed from the distribution line work I saw in the 50's and 60's is that back then, the conductors were usually a lot thinner gauge and seemed to be sagged a lot looser than they are today.

Beachcomber

Reply to
Beachcomber

| Apparently faults can be anything from trees falling on the lines to | exploding transformers or sometimes when the winds picked up, the | lines would swing into each other and start arcing which was really | scary if you were just driving around.

One thing that is fun to see is when the source of the mechanical energy swinging the lines is from one end, propogating the switch along the line. Then you can see the arc traveling down the line.

Reply to
phil-news-nospam

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.