A strain insulator is an
electrical insulator
An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials—semiconductors and conductors—conduct electric current ...
that is designed to work in mechanical
tension (strain), to withstand the pull of a suspended electrical wire or cable. They are used in overhead electrical wiring, to support
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a tr ...
antenna
Antenna ( antennas or antennae) may refer to:
Science and engineering
* Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves
* Antennae Galaxies, the name of two collid ...
s and
overhead power line
An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-p ...
s. A strain insulator may be inserted between two lengths of wire to isolate them electrically from each other while maintaining a mechanical connection, or where a wire attaches to a pole or tower, to transmit the pull of the wire to the support while insulating it electrically. Strain insulators were first used in
telegraph
Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas ...
systems in the mid 19th century.
Description and use
A typical strain insulator is a piece of
glass
Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...
,
porcelain
Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises main ...
, or
fiberglass
Fiberglass ( American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cl ...
that is shaped to accommodate two cables or a cable shoe and the supporting hardware on the support structure (hook eye, or eyelet on a steel pole/tower). The shape of the insulator maximizes the distance between the cables while also maximizing the load-bearing transfer capacity of the insulator. In practice, for
radio antennas,
guy-wire
A guy-wire, guy-line, guy-rope, or stay, also called simply a guy, is a tensioned cable designed to add stability to a free-standing structure. They are used commonly for ship masts, radio masts, wind turbines, utility poles, and tents. A ...
s,
overhead power line
An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-p ...
s and most other loads, the strain insulator is usually in physical
tension.
When the line
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
requires more insulation than a single insulator can supply, strain insulators are used in series: A set of insulators are connected to each other using special hardware. The series can support the same strain as a single insulator, but the series provides a much higher effective insulation.
If one string is insufficient for the strain, a heavy steel plate effectively bundles several insulator strings mechanically. One plate is on the "hot" end and another is located at the support structure. This setup is almost universally used on long spans, such as when a power line crosses a river, canyon, lake, or other terrain requiring a longer than nominal span.
Strain insulators are typically used outdoors in overhead wiring. In this environment they are exposed to rain and, in urban settings, pollution. As a practical matter, the shape of the insulator becomes critically important, since a wetted path from one cable to the other can create a low-resistance electrical path.
Strain insulators intended for horizontal mounting (often referred to as "dead ends") therefore incorporate flanges to shed water, and strain insulators intended for vertical mounting (referred to as "suspension insulators") are often bell-shaped.
Hoover Dam
Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on S ...
Collectors
Other than their industrial use for which they are produced, strain insulators can be
collectable
A collectable (collectible or collector's item) is any object regarded as being of value or interest to a collector. Collectable items are not necessarily monetarily valuable or uncommon. There are numerous types of collectables and terms t ...
s, especially antique ones.
References
{{reflist
External links
US collectors club for glass insulators
Overhead power lines
Electric power distribution