DIYbanter - View Single Post

Bruce in Bangkok[_5_]

On 15 May 2008 05:20:27 GMT, wrote:

In alt.engineering.electrical Michael Moroney wrote:

| Phil, did you see daestrom's excellent explanation how they use an
| inductor to prevent a dead short but in a way such that the inductor is
| virtually not there during normal operation (counterflowing currents)?

I believe I missed that.

| If these tap changers are rather expensive, I'm wondering what those
| pole pig "voltage regulators" I mentioned are. I thought they were just
| tapped autotransformers.

Sounds like they may be more of a voltage selector.

One set of transformers I saw once had a voltage selector which also revealed
the voltage to me. Even those these huge things were well guarded behind a
chainlink fence with barbed wire on top, I could clearly read the instructions
on the voltage taps. It listed 5 or 6 different voltages in the 4160 volt
range (I believe that was a middle one). The secondaries were a thick bundle
of insulated wires not on insulator standoffs, so obviously LV, possibly 480V
or 208V. These were 3 single tank transformers in roughly the design style
of a pole pig (round tank) with a control panel on them with the tap control
and some gauge I guessed may be temperature (but I could not see it clear
enough at the distance I was at to be sure). The instructions did indicate
that the transformer must be de-energized (not just unloaded) when making the
change. So I'm guessing they were just to compensate for variations in the
delivered voltage. These transformers were about 1 meter wide and 2.5 meters
high, each (3 of them). I did not see any reference to a kVA rating. They
were also very old looking (pre-WWII). They were humming.

All distribution transformers, sometimes called "pole pigs", that I
have seen had some sort of voltage adjusting system, usually referred
to as taps. Usually they are an actual bolted "tap" and you open the
transformer and set the output voltage by making the proper tap
connection when the transformer is installed and frankly it is usually
ignored thereafter.

The other "cans" you often see on poles are capacitors used to adjust
the power factor on some secondaries.

Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)