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Transmission & Distribution: Insulators

This Exhibit Contains 15 Items
1
Glass electrical insulator, ca. 1880

Glass electrical insulator, ca. 1880

Item 74833 info
Maine Historical Society

Most of Maine’s electrical grid is wired on utility poles; only urban areas such as Portland and the cities of Auburn-Lewiston have significant underground systems.

What is on the poles? The three wires at the top are distribution wires—they carry electrical power from the local substation to the customers.

These wires, which operate at 12,470 volts, are mounted on porcelain insulators to prevent the current from "leaking," which would waste it or create a hazard.

The insulators and distribution wires are mounted on a wooden crossarm. Insulators are used in other parts of the system as well.

Insulators are made of a variety of materials and come in an array of special shapes, each intended to provide a particular function.


2
Provo-type electrical insulator, ca. 1897

Provo-type electrical insulator, ca. 1897

Item 74830 info
Maine Historical Society

This style of glass insulator was originally made in 1898 for the Telluride Power Transmission Company in Provo, Utah, which used it to construct a long high voltage line.

It proved unreliable at high voltage, but worked well at lower voltages, and remained a popular technology for 22kV transmission lines throughout the United States until porcelain multipart insulators were developed.


3
Pin-type electrical insulator, ca. 1897

Pin-type electrical insulator, ca. 1897

Item 74827 info
Maine Historical Society

This insulator, a type made in late 1896 and early 1897 by the Imperial Porcelain Works of Trenton, New Jersey, was used in the Sanford area.

It was an early porcelain insulator and proved so popular that the plant could not keep up with the demand and quality suffered.

By the 20th century, however, porcelain replaced glass as the most common insulator material.


4
Pin-type telephone line insulator, 1888

Pin-type telephone line insulator, 1888

Item 74829 info
Maine Historical Society

This "toll style" telephone-line insulator was installed as part of the Old Orchard Beach Fire Department alarm system sometime between 1890 and 1920.


5
Open-end strain insulator, ca. 1900

Open-end strain insulator, ca. 1900

Item 74837 info
Maine Historical Society

These insulators were nicknamed "egg strains" because of their shape. This insulator works under compression, the guy wires pulling through the center of the insulator rather than outwards from the ends.

The crossed wire grooves also allow the guy wires to remain connected should the insulator break.


6
Porcelain multi-part electrical insulator, ca. 1912

Porcelain multi-part electrical insulator, ca. 1912

Item 74831 info
Maine Historical Society

This insulator is constructed of three parts: the upper dome with the saddle at the top and the two conical skirts at the bottom.

Insulators such as this one were used on high-voltage transmission lines of up to 69,000 volts.


7
Break-strain insulator, ca. 1915

Break-strain insulator, ca. 1915

Item 74835 info
Maine Historical Society

This strain insulator, used on the support structures for overhead electric railway lines, was found in the Rockland area.

Strain insulators are used on guy wires supporting utility poles or radio antennas to break the electrical path and prevent short circuits or grounding.


8
Pint-ype insulator, ca. 1916

Pint-ype insulator, ca. 1916

Item 74828 info
Maine Historical Society

Pin-type insulators similar to this Lapp #6183 are still used on utility poles today.

This "pin-type" insulator has a socket in the bases that screws onto threaded wooden or metal "pins" mounted on the utility pole.


9
Pintype electric insulator, ca. 1916

Pintype electric insulator, ca. 1916

Item 74823 info
Maine Historical Society

The threaded pin-type insulator was patented in 1865.

Earlier insulators were secured to the pins by various means such as padding with burlap, or perhaps sticking down with tar.


10
Electrical insulator pin, ca. 1917

Electrical insulator pin, ca. 1917

Item 74824 info
Maine Historical Society

The pin is part of a type of electrical insulator.

The insulator with the pin (that screws into the base of the porcelain insulator) was patented in 1865.


11
Westinghouse #104 insulator, ca. 1920

Westinghouse #104 insulator, ca. 1920

Item 74834 info
Maine Historical Society

This type of insulator is sometimes called a "side-tie" insulator, and may have been used for either domestic service distribution or telephone and telegraph lines.

This insulator was recovered from a pole in Westbrook.


12
Ball-strain insulator, ca. 1920

Ball-strain insulator, ca. 1920

Item 74836 info
Maine Historical Society

Nicknamed the "Johnny Ball," this insulator is made of a composite material containing asphalt, shellac and asbestos.

Strain insulators are used in the guy wires supporting utility poles or radio antennas to break the electrical path and prevent short circuits or grounding.


13
Electrical insulator, ca. 1930

Electrical insulator, ca. 1930

Item 74825 info
Maine Historical Society

This insulator is coated with a composite material containing particles of mica, a mineral also used to insulate early toaster elements, fuses, and switches.


14
Rubber pin-type insulator, ca. 1930

Rubber pin-type insulator, ca. 1930

Item 74826 info
Maine Historical Society

Rubber insulators were a common replacement for glass pin-type insulators on telephone lines between 1930 and 1980.

In some areas, the glass insulators had proved tempting targets for thrown rocks or gunfire.


15
Pony insulator, 1933

Pony insulator, 1933

Item 74832 info
Maine Historical Society

Alexander Graham Bell invented twisted-pair telephone wiring in 1881 by to stop interference of electrical and telephone lines on the same utility poles.

The Hemingray No. 10 "pony" insulator was developed to accommodate this new wiring system, with square grooves set close together and a thicker, sturdier construction than earlier communication insulators.

The No. 10 soon became the standard communications insulator.


This Exhibit Contains 15 Items