Everything you need to know about high voltage glass insulators

A high voltage glass insulator is an element designed to support and insulate high voltage electrical conductors in electrical energy distribution and transportation systems. It is composed of a tempered glass disc that can have different shapes depending on its function and specific application, to which a metal cap and pin are attached that allow the insulators to be joined forming insulator strings. These insulators are essential to maintain the integrity of the electrical system and prevent short circuits or electrical shocks.

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• It is designed to withstand high voltages.
• It can have different shapes depending on its function.
• It is essential for the integrity of the electrical system.

Each insulator model is defined by a series of parameters defined by the manufacturer and can be seen in the catalogue or on the drawings of each insulator, and which must comply at least with the minimum or maximum values ​​required by the different applicable standards The main parameters include the mechanical (mechanical breaking load), the dimensional (coupling standard, diameter, creepage distance and pitch), the geometric (shape of the insulator profile) and the electrical ones (electric withstand voltages for puncture, dry and wet power frequency, and lightning impulse withstand voltages). For each power line project, the required chain parameters must be properly calculated, and the most appropriate insulators must be chosen for each case.

• Mechanical parameters
• Electrical parameters
• Dimensional and geometric parameters

Proper installation and maintenance of high-voltage glass insulators are essential to ensure their optimal operation and prolong their lifespan. The installation process typically involves securely fastening the insulators to support structures using appropriate hardware and tools for the specific environment. Additionally, in highly polluted environments, regular inspection procedures should be followed to detect excessive contamination, and corrective measures should be taken as necessary to prevent premature failures.

• Secure fastening to support structures.
• Regular inspection to detect excessive contamination.
• Proper maintenance to prolong lifespan.

High-voltage glass insulators are primarily made of high-quality tempered glass, which is capable of withstanding significant mechanical and thermal stresses, while also enduring high levels of electrical tension without damage.

In addition to glass, complementary materials such as cast iron, forged steel, cement, and stainless steel are used for the fastening fittings. These materials are designed to withstand adverse environmental conditions and ensure the stability and durability of the insulator throughout its lifespan.

For very high contamination environments, the SILGLASS® solution adds a thin layer of room temperature vulcanizing (RTV) silicone to the glass surface of the insulator, which imparts hydrophobic properties, adding performance benefits against contamination.

• High-quality tempered glass.
• Metallic materials for the fittings.
• Cement as a fastening element for the components.
• RTV silicone coating for SILGLASS® insulators.

Contamination, such as the accumulation of salts, dust, or other natural or artificial elements, combined with moisture on the surface of glass insulators, can significantly affect their performance and effectiveness. This contamination can lead to a decrease in the dielectric strength of the insulator chain, increasing the risk of electrical arcs and shocks. On the other hand, excessive contamination without taking mitigation measures can potentially accelerate the aging of insulators due to corrosion.

• Decrease in the insulation capacity of the chains.
• Increased risk of electric arcs.
• Potential accelerated aging of insulators.

To mitigate the effects of pollution, several measures can be taken. First of all, the type of contamination that affects the line must be studied (sources, characteristics of the contaminant, etc.) and the severity of the pollution at the location must be determined. You must choose the appropriate insulator profile for each environment (standard, anti-pollution, aerodynamic…), design the chains with sufficient specific creepage distance. Also install adequate protection against corrosion (sacrificial zinc ring, standard or reinforced galvanization). And in extreme cases, minimize leakage current by applying RTV silicone creating a hydrophobic layer to the insulators.

• Analysis and study of contamination
• Proper selection of the profile of the insulators and the creepage line of the chains
• Protection against corrosion
• RTV silicone application

High voltage glass insulators are subject to specific standards or technical specifications that regulate their design, manufacturing and testing. These regulations may vary by country but are usually guided by the standards established by the International Electrotechnical Commission (IEC) or the American National Standards Institute (ANSI). These standards provide detailed guidelines on the quality requirements that insulators must meet to ensure their suitability and reliability in high voltage applications.

• Standards for design, manufacturing, and testing.
• International standards such as IEC and ANSI.
• Quality requirements.

In addition to glass insulators, there are porcelain insulators and polymer insulators.

Glass insulators, like porcelain ones, are cap and pin insulators or chain insulators that are coupled together to form insulator strings, whereas polymer insulators are single-piece elements.

The most important advantages of glass insulators over porcelain and composite or polymeric insulators are the following:

• Ease of visual inspection: A glass insulator, when it has a defect or is perforated, shatters completely, making it easily detectable with the naked eye from the ground without the need for expensive inspection systems. Even if an insulator shatters, both the mechanical and electrical properties of the insulator string remain almost intact (LGI guarantees a residual strength of the “insulator whose insulating part has shattered” of at least 80%, and the loss of leakage distance in the entire string is relatively small), so urgent action is usually not necessary. The insulator can be replaced later during the next scheduled maintenance operation. In any case, the annual rate of spontaneously shattered insulators is statistically very low with experienced and high-quality glass manufacturers, with less than 1 insulator shattered per 10,000 insulators in service.
• Greater durability: Glass insulators do not degrade and have a longer lifespan compared to others, especially polymer insulators. The lifespan of a glass insulator exceeds 50 years, often exceeding the expected lifespan of the electrical transmission line.
• High mechanical and electrical strength: Glass insulators are known for their higher mechanical and dielectric strength.
• Environmental advantages: Its longer lifespan, the fact that glass is a 100% recyclable material, and its manufacturing process having a lower environmental impact make glass insulators more sustainable than others.
  • Greater ease of inspection
  • Greater durability
  • High mechanical and electrical strength
  • Environmental advantages

The use of high voltage glass insulators can provide several environmental benefits compared to other types of insulators. For example, and unlike polymeric insulators, the expected useful life of a glass insulator is greater than 50 years, which usually exceeds the useful life of the line itself; This means that throughout the life of the line it is not necessary to renew the insulation, reducing the number of insulators that need to be manufactured and saving those associated resources.

On the other hand, glass is a recyclable material, which means that glass insulators at the end of their useful life can be recycled and reused instead of being disposed of in landfills. Additionally, glass insulators require fewer natural resources to manufacture compared to other materials such as porcelain, contributing to the conservation of natural resources and reducing the environmental impact associated with the production of electrical insulators.

• Longer lifespan than that of the line.
• Recyclable material.
• Lower consumption of natural resources.
• Reduction of environmental impact

By Dario DiMare

OK folks, I’ll be honest—I don’t even know where to begin. Asking me to write an article on insulators is like asking a grandparent to write an article on their grandchild. A zillion pages later and I am still writing.

I will start off with just a little bit about me. I started collecting insulators in . I was actually digging for bottles in Ashtabula, Ohio, where I was born and raised, when I dug up an insulator with an date on it. Nobody knew what the date meant, but we knew the insulator was old. I was 10 years old at the time. I looked it up in the libraries but found nothing.

My first insulator, dug in Ashtabula, Ohio in . CD 131 Brookfield, Patent July 25, . See below to learn about CD numbers.

Six years later, I lied to my mother about sleeping over at my best friend’s house. With a new driver’s license in hand, I jumped in my $50 Pontiac Catalina and drove 400 miles to Washington, DC, to look up the patent at the Library of Congress in the National Archives. Gas was about 50 cents a gallon, and I had one loaf of bread, one jar of peanut butter, a moving blanket, and a half-gallon bottle of water (which was glass back then). So, by stealing the peanut butter and bread from mom, filling the water up in the gas station bathrooms, and sleeping in the back seat of the car, the total round trip to DC and back cost about $30. It took a lot of Dr. Kilmer’s and blob top soda bottles sold to the antique shops to get the $30. The July 25th, date was the patent for screw threads in insulators. I still have the insulator.

Now having owned as many as 12,000, and having handled more than ten times that amount, with thousands of hours spent hunting and researching, I feel comfortable writing a little about insulators.

Here is some fundamental information about insulators.

What are insulators?

Insulators are non-electrical conducting objects, usually made of glass or porcelain, intended to insulate the current running in a wire from grounding out, especially in fog or rain. Most often they are mounted on wooden pins on the cross arms of poles. If they insulate properly, the electric signal or current will meet its final destination in a safe and useful manner.

What are insulators made out of?

Most insulators in the U.S. were made of glass or porcelain. There are some composite, gutta-percha, rubber, and even wooden insulators. I will be speaking primarily about glass insulators since they are my specialty (with the exception of very early telegraph insulators which were made of various materials including porcelain).

Materials: Telegraph insulators made out of glass, gutta percha, composition, wood, metal, and one of the earliest plastics ever made.

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Ramshorns: Very early ramshorn type insulators. The ramshorn itself is iron. They are set in glass, gutta percha, rubber, and composition.

Porcelain threadless: A very rare and diverse collection of threadless insulators made out of porcelain.

How old are insulators?

Glass insulators emerged in s America with the invention of the telegraph. The early telegraph insulators were mostly threadless, pin-type insulators. There were some glass blocks and ram’s horn types as well. The very first glass insulator, the bureau knob, was used by Samuel F. B. Morse on the line from Baltimore to Washington. The first electronic telegraph message in May of stated “What hath God wrought?”

Left: This is the first glass pin-type insulator first used in the s. CD 780, Bureau Knob. Right: The 780 and the glass blocks were the first insulators used on the telegraph and date back to the s. CD 780 and CD glass blocks.

The threadless insulators are kind of like pontil bottles, with a similar end date of about to when my buddy Louis A. Cauvet patented the threaded insulator. The threadless were also primarily used on telegraph lines, since the was not invented until , when Alexander Graham Bell said to his assistant, “Mr. Watson—come here—I want to see you.”

Threaded insulators were then made by the millions and used throughout the world. Many of the glass houses that made bottles made insulators as well. The last glass insulators were made by Kerr in the early s. Yup, the same guys that made the fruit jars.

Left: This is a pair of transition insulators. Like with some bottles, there are both pontil and non-pontil bottles using an identical mold. These insulators have the same outer mold and only the plunger forming the threadless or threaded pin hole are different. CD 736 threadless and CD 135.5 threaded E.R.W.’S. Right: This is the last glass insulator ever made. How depressing! Waaaaaah! CD 155 Kerr.

What color are insulators?

Put very simply, insulators are made in every color that bottles, china, and windows were made in. Back then, in almost all cases, the color did not matter. A lot of insulators were made from “end of the day” glass; instead of throwing out the batch of glass at the end of the day, glass makers would fill up insulator molds and sell them by the hundreds. Appearance was not a big deal with insulators. I have a few “crystal” insulators made in Sandwich, Massachusetts. Imagine turning one of these babies up-side-down and drinking champagne out of them so you could fit in with the bigwigs?

The shelf above has the complete rainbow of color on it: red, orange, yellow, green, blue, and purple. Like bottles, aqua is the most common color, but some of the rarest insulators are aqua. A few insulators were factory-coated with carnival glass or a flashed amber. The most sought after colors are cobalt blue, yellow, 7-Up green, and purple. Some of the purple insulators were originally made clear, but due to the sun’s effect on the manganese in the glass, they actually turned purple.

What makes a “good” insulator “good”?

Like with bottles, there are many factors that make an insulator “good” or more desirable. Here are a few of the factors:

Condition is a big deal with most insulators. There are fewer mint condition insulators than bottles, due mostly to the industrial use. Rare insulators in mint condition command a premium.

Color is very important. A $10 insulator commonly found in aqua can fetch you $10,000 in a rare color. And there are a few cases like in the CD 701.6 where the aqua insulator is worth five times more than the dark green CD 701.6.

I just had to put this in. The manufacturer of this CD 121 is R. Good Jr. out of Denver, Colorado. Pretty hard to argue about this being a “good” insulator. Ha! CD 121 Good. 

Age also adds value. Most threadless insulators are worth more than threaded insulators. However, the ten most valuable insulators in the hobby are threaded. I am not being a wise guy, just being honest. 

Embossing is also a major factor. Having just common embossing can add value. Having a rare embossing can add even more value. The CD 150 Brookfield books for about $500, and the CD 150 Barclay books for $5,000!

Rarity obviously adds value. I know of some CDs where I am almost certain that fewer than a dozen exist. They may have made hundreds or thousands, but to my knowledge, very few have survived, and the ones that have are very difficult to find.

Desirability is the big wild card. Some insulators are just more desirable than others. This makes no sense when you look at statistics, numbers, color, or age. Some are just flat out more desirable. I know of about five or ten CD 100.2s and CD 100.6s. They are extremely rare, and yet the CD 141.9, of which I know of about 20 or 25, still fetches two or three times more on the market.

The 100.2 is extremely rare and books for several thousand dollars. The 141.9 is not nearly as rare and books for three or four times more than the 100.2. (Please be careful if buying a CD 100.2. The CD 100 is very similar looking, and the CD 100 is very, very common, and valued at one dollar or less.) CD 100.2 Surge and CD 141.9 Emminger’s.

What is a CD?

CD stands for Consolidated Design and is the numerical designation used to identify glass insulators. U numbers are used for porcelain, and M numbers are used for multi-part porcelain insulators. N. R. “Woody” Woodward invented the CD system in the early s. He was an early collector and researcher, solely responsible for categorizing all of the glass insulators in North America. He partnered with Marilyn Albers to assign CD numbers to the foreign glass insulators. There is some logic to the numbering system with simple pin type insulators starting at CD 100 and ending at CD 350; the threadless claiming the CD 700s; and some of the block types and more unusual shapes reaching the s. When listing an insulator for sale we usually state it as CD#, name, color, condition, and price.

For example: CD 731, Tillotson, aqua with bubbles, mint $0.00

I was asked by N. R. Woodward to take over the CD assignments for the insulator hobby, so now I am responsible for assigning any new CD. We have the National Insulator Association (NIA) at www.nia.org as our national association and Insulator Collectors On the Net ICON at www.insulators.info as a great collectors chat and web site. 

This is my favorite insulator which I dug up in New York in . Great condition and 1,444,444 seed bubbles, which I counted all by myself. CD 731 Tillotson.

If you have any questions about insulators, please feel free to contact me. Let me know your time limit, because I can ramble on forever about these stupid things. Happy collecting!

You can reach Dario by mail at Dario DiMare, 318 Main Street, Northborough MA . Give him a call with your insulator questions at (617) 306-. And, send your insulator mysteries and photos to .