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Electrical Insulators

How It's Done: Electrical Insulators


You’ve definitely seen them, and you've probably wondered what they are. They have an odd, cylindrical shape, like a stack of teacups or discs, attached to utility poles or high voltage transmission lines. These are insulators, and Andy Shwalm knows a thing or two about them.

Andy is the technical director of the oldest insulator manufacturer in the U.S. Located in Victor, New York, Victor Insulators has been in the business since 1893 and still ships about 10,000 tons of product per year. Andy explained what insulators do and demonstrated the precision and craft that go into manufacturing these essential pieces of our electrical infrastructure.

This interview has been edited for clarity.

The Importance of Insulators

Overhead power lines are insulated by air. It’s the air gap around them that prevents electricity from flowing or arcing from the lines to somewhere you don’t want it to go. What an insulator does is to maintain that air gap.

Without insulators, we wouldn’t be able to transmit electricity from where it’s generated to where it’s used. You wouldn’t have electricity for air conditioning, running the lights or charging your phone.

An insulator needs to be totally nonconductive, and it needs to withstand the voltage without ever breaking down. And the shape of the insulator is important. The shape is designed to have a lot of creepage – that’s the distance along the insulator’s surface from the conductor end to the ground end. Having a large creepage distance prevents arcing that would flash over the insulator. And the shape also helps prevent the accumulation of rainwater, snow or dirt that can interfere with the insulating properties.

The Raw Materials

We’re using raw materials, which are quite literally dug up out of the ground, to make a finished product. There are three kinds of materials that we use. We get them as powders.

The main group is clays, which provide the plasticity. Then there’s the fluxing agent, which is feldspar, basically decomposed granite. Then there’s the filler material. We use two different fillers, silica sand and aluminum oxide.

When we mix these materials and fire them in a kiln, what's happening is that the feldspar and the clays react to form a glassy phase, and that glassy phase surrounds the filler particles. Ultimately, the fired porcelain is a glassy phase with filler particles of either silica or aluminum oxide embedded in it.

Mixing the Clay

For porcelain to happen, we need to mix the materials as finely and completely as we can, which means using a very large amount of water. We mix it into something that looks like a milkshake. At this point it’s about 50% water by weight.

Then we need to take most of that water back out. We filter-press it back down to about 16% to 18% water. That gives us a stiff clay.

We also need to get the air out of the clay. We run it through a vacuum extruder, which shreds the clay up under a vacuum and recompacts it into a cylinder.

These cylinders can be shaped on a lathe or other turning tool. For some shaping processes, we need to dry the clay first. We dry it very slowly. If it dries too fast it will crack, like a mud puddle heating up in the sun.

Firing the Cylinders

Porcelain is an odd material because it doesn't exist naturally. To make it exist, you need to put a tremendous amount of energy into it. It requires chemical reactions that don’t want to happen.

Heat is what drives those chemical reactions forward. The kilns fire at about 2,300 degrees F, and our products are in there from three to six days.

All the heat energy that goes into making porcelain is also one of the reasons it’s such a good insulating material. It takes so much energy to make it, and it takes just as much to unmake it. That’s why you can dig up a Ming vase that’s hundreds of years old and still intact.

The composition of porcelain also makes it nonporous, which is important for us. You can put one of our insulators in a tub of water and leave it there for 50 years – it will absorb absolutely no moisture. This is critical for insulators because moisture and electricity do not mix.

Controlling the Dimensions

We add metal fittings to some of our insulators. For example, a switch manufacturer might want to install the insulator on his product, so we would need to put metal fittings on it.

During the assembly stage, we need to ensure the dimensional integrity of the insulator. It sounds easy to say, “I'm just going to cement two metal caps on a piece of porcelain,” but there are requirements for the orientation of the caps, the length of the insulator, the parallelism of the caps. There are a bunch of characteristics that need to be maintained, so the process is not that simple. We need to control all the critical dimensions.

Testing and Shipping the Product

Every single insulator is tested prior to shipment to ensure its integrity. Some of the testing is very simple. We flash over the insulator at ultra-high frequency or three to five minutes at 60 cycle frequency, just to ensure there are no defects. Other products, such as large station posts, we’ll mechanically test at about 50% of their rated strength.

Porcelain is somewhat fragile, so packaging is very important, both for handling the product and protecting the product. One of our real costs is packaging. We’re always working on how we can adequately protect the product in an efficient way.

The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.