Berkshire Insulator Gallery

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How transmission line insulators are assembled and disassembled.

I have been asked several times how large transmission line suspension insulators are assembled and disassembled.  Many visitors who see strings of these up close for the first time are amazed at how flexible the strings are and that there doesn't appear to be anything holding them together.  And some people when they first pick up a string (if they are strong enough to do that) are afraid they are going to fall apart on them.  They also don't understand how they can insulate the line with the metal caps and pins all connected together.

Here is a string of 6 small blue porcelain insulators.

Short string of insulators

The way these insulate is the porcelain is between the metal cap and the metal pin.  Normally in modern insulators the cap is crimped onto the outside of the porcelain or glass and the ping is cemented into a hole in the bottom.  The rest of the porcelain or glass is there to provide a longer distance for current to try to flow from the cap to the pin than the short distance through the insulator material.

Short string of insulators

This shows a few short stacks of insulators in my holding area.  All of the glass and the white porcelain are firmly locked together... believe it or not.  The large angles on some of the stacks show you just how much room there is for movement between insulators even when they are locked together.  In all cases i have seen there is not quite enough movement for the two insulator's glass or porcelain to touch.  This limits how many you can stack vertically like this.  I have found that you can only stand up 2 or maybe 3 in a stack, beyond that they may want to tip over.  Also some of them have longer pins that prevent them from sitting flat on a hard surface.

Here is a shorter string of 2 that i will take apart and put back together. 

Short string of insulators

These are all the tools that are needed... a long screwdriver and a crescent hammer.

Short string of insulators

Under the hood there is only 1 moving part.  What looks like a big bent up cotter pin is all that holds two insulators together.  When it is in the locked position it looks like this.

Short string of insulators

And in the unlocked position it looks like:

Short string of insulators

An important note, when collecting these, don't remove the pin, or try to straighten it... it is meant to have all those bends and should never have to leave the insulator.  The hump in the ping on the picture above is what keeps the pin from moving out when it is in the locked position.  The spread of the ends of the pin on the inside of the cap keeps the pin from coming all the way out, and also is what prevents the insulators from slipping apart.

Ok, here are the two dirty insulators locked together.

Short string of insulators

You are looking down the shaft of the long screwdriver.  The screwdriver is positioned on the end of the cotter pin.  It is hard to see but when you look at these closely the key to them staying together is that the cotter pin is just big enough to prevent the pin from the top insulator from slipping out the slot in the bottom one.

Short string of insulators

Give the screwdriver a sharp rap with the crescent hammer and the pin pops out to the unlocked position.  WARNING, don't just pull out the screwdriver, grab hold of the metal cap first to prevent it from falling down and hitting the inside of the top insulator's glass or porcelain and damaging it.

Short string of insulators

The two insulators are now apart.  To put them together you just turn the bottom one over and slip it over the pin of the top one.

Short string of insulators

Position the screwdriver on the end of the cotter pin and give it a rap with the crescent hammer again, and the pin snaps into the locked position.

Short string of insulators

The insulators in the above example are some of the easy ones because the pin is exposed and you can get the screwdriver on it to punch it in and out.  Some of them are not so easy though.  The set below has longer glass skirts so you can't get the screwdriver into place directly.

Short string of insulators.

See in these dirty ones that the pin is hard to get to because of the longer glass skirt.

Short string of insulators

In this case you work on the back of the pin and make use of the crescent hammer as a fulcrum to pry the pin gently out of the cap.  Be careful that you don't smack the inside of the glass with the crescent hammer.  If you are in the field and don't have a crescent hammer you can substitude a small branch or second screwdriver, just something to give you a bit of a lever to pop the pin out to unlock it.

Some other tidbits on hardware.

Short string of insulators

This is a piece of hardware that would hang from the bottom insulator in a string to support the hardware that holds the wire.  The cotter pin on the left side works the same as the one on the cap of an insulator to lock the hardware to the bottom of the string.  Note that it is still free to rotate and tip to line up with the hardware below it.

Short string of insulators

This is one that goes in the top of a cap to hold a string onto a tower arm (here it just attaches to a different kind of insulator.  Some people would think this is bent and damaged, but this is the way it is designed.  The bend lets the insulator string hanging below it move freely in all directions without trying to bend the arm above it.

 



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