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Posted by TKM on June 23, 2008, 2:12 pm
>>Joe wrote:
>>
>>> On May 18, 1:04 am, letter...@invalid.com wrote:
>>>
>>>>In rural areas I often see on power poles these things that look like
>>>>small transformers, which are not near any buildings. They are on the
>>>>primary lines, which I understand are generally around 15KV. These
>>>>look similar to the transformers used by homes and buisnesses, except
>>>>they are smaller, particularly smaller in diameter. They only have
>>>>two insulators on the top. They hang on a pole. The wire coming to
>>>>that pole enters one of the insulators, the wire leaving that pole
>>>>(going to the next pole) is on the other insulator. In other words
>>>>they are in series with the wires and on the HOT side. The ground
>>>>wire (lower on the pole) is not affected at these poles, it just
>>>>continues on.
>>>>
>>>>What are these things for? What do they do?
>>>>
>>>>I should mention that I have seen THREE of them on poles that furnish
>>>>3phase power (4 wires with the ground). Each of the 3 wires goes to
>>>>one of these things.
>>>>
>>>>Thanks
>>>
>>>
>>> They are power factor correction capacitors. Every long service line
>>> must have these at predetermined intervals to keep the current and
>>> voltage in phase. In industrial plants some distance from a
>>> substation, machines like welding rigs will even have built in
>>> capacitor power factor correction to reduce current draw. Visit any
>>> power company supply yard and you will see the capacitors stored with
>>> the switches and distribution transformers. You may find a friendly
>>> engineer in the office to explain the deal for you. HTH
>>>
>>> Joe.
>>
>>If they are in series with the lines, they are not power factor correction
>>capacitors. To be power factor correction capacitors they would have to
>>be
>>connected line to line or line to neutral.
>
> That final paragraph -- could someone explain them in a bit more detail?
>
> Thanks,
>
> David
>
Power factor-correcting capacitors are usually rectangular metal boxes
fastened on a cross-arm near the top of the pole.
Is there a small loop on the devices in question? If so, the device is a
switch/fuse that is designed to open the line at that point. The utility
crew has a long insulated pole that hooks on to the loop so they can operate
the switch from the ground or bucket truck.
If there is no loop, I'll guess that the cylinder is a lightning arrestor
that will short the high voltage from a lightning strike to ground.
TKM
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