Re: What are these power pole transformers for?
- From: bud-- <remove.budnews@xxxxxxx>
- Date: Sun, 18 May 2008 11:13:55 -0500
Steve B. wrote:
What are these things for? What do they do?
Here's an answer from our family electrical inspector...
Steve B.
"Oil circuit breakers and/or re-closures…
95% of things in series (on power lines) are some type of switch.
Often you will see they also have a fuse in parallel to them (but
open)..the fuse is in series with the power line also.. the fuse is
there, to be manually closed, in the event the C/B goes bad or needs
servicing.
Because of the voltage, if the breaker needed to open, especially
under "fault" (short) the amperage it needs to break might be
thousands of amps, therefore , the operation is all contained in a
canister filled with non-conductive oil. The contacts opening in oil,
without air, prevents flash & damage to the C/B.
They could be re-closures or a combo beaker/re-closure. Re-closures
are critters that, as their name says, reclose the line. They are set
for a certain amount of times (usually 3) so if something happens like
a squirrel gets on the transformer, the squirrel shorts, the breakers
opens, light go out.. the "blast" at the transformer ends with the
squirrel flying, clearing the "fault". The re-closure, in a preset
time, closes the line back minimizing the outage.
A little longer answer:
Imagine rural distribution starts from a point with distribution wires going out like a tree. If you have a fault at some point you want minimal disruption of the distribution. Everything downstream from the fault would be disconnected and everything else would be on.
You could put fuses at 1 mile, 2 miles, ... from the feed point to isolate the fault. The problems is that a fault at 5 miles is likely to blow the fuses at 4 miles, 3 miles, 2 miles, 1 mile. The outage is not minimized.
A method commonly used is to put "sectionalizers" at 1 mile, 2 miles, 3 miles. At the source is a "recloser". On a fault, the recloser opens.
If there was fault current at the 3 mile sectionalizer, the fault is beyond that sectionalizer and when the recloser opens that sectionalizer will open.
The recloser then closes. If there is still a fault the recloser opens again. If there was fault current at the 2 mile sectionalizer it will open. The recloser connects again....
Sectionalizers 'count' the reclosures and open depending on how they have been set, which depends on how many sectionalizers there are to the recloser. After the closest sectionalizer would have opened, if there is still fault current the recloser stays open. The result is only the minimum required part of the system is killed.
Sectionalizers always open when the circuit is dead so they don't have to open on fault currents. That means they can be pretty small. That is probably what you saw.
Reclosers do open on fault current - multiple times. They have to be quite large, more like a refrigerator or larger.
You need a sectionalizer (and recloser) in each hot wire. With 3 phases on the pole you need 3.
--
bud--
.
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