Guy-wire

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A yacht's mast is supported by shrouds and stays - nautical equivalents of guy wires. Schema-greement-TETE.png
A yacht's mast is supported by shrouds and stays - nautical equivalents of guy wires.

A guy-wire, guy-line, or guy-rope, also known as 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 thin vertical mast supported by guy wires is called a guyed mast. Structures that support antennas are frequently of a lattice construction and are called "towers". One end of the guy is attached to the structure, and the other is anchored to the ground at some distance from the mast or tower base. The tension in the diagonal guy-wire, combined with the compression and buckling strength of the structure, allows the structure to withstand lateral loads such as wind or the weight of cantilevered structures. They are installed radially, usually at equal angles about the structure, in trios and quads. As the tower leans a bit due to the wind force, the increased guy tension is resolved into a compression force in the tower or mast and a lateral force that resists the wind load. For example, antenna masts are often held up by three guy-wires at 120° angles. Structures with predictable lateral loads, such as electrical utility poles, may require only a single guy-wire to offset the lateral pull of the electrical wires, at a spot where the wires change direction.

Contents

Conductive guy cables for radio antenna masts may disturb the radiation pattern of the antenna, so their electrical characteristics must be included in the design.

Uses

Closeup of anchor end of three guy-wires used to support the KVLY-TV mast in North Dakota, the tallest guyed mast in the world. Each guy is one member of a set of three that is located radially around the tower KVLY-TV tower, North Dakota 019.jpg
Closeup of anchor end of three guy-wires used to support the KVLY-TV mast in North Dakota, the tallest guyed mast in the world. Each guy is one member of a set of three that is located radially around the tower
Guywire.jpg
Guy-wire supported mast.
KBRC antenna tower guy wires.JPG
AM antenna tower with guys attached through strain insulators at 120° angles

Sailing

The guys supporting a sailboat mast are called "standing rigging" and in modern boats are stainless steel wire rope. Guys are rigged to the bow and stern, usually as a single guy. Lateral guys attach to "chain plates" port and starboard attached to the hull. Multiple guys are usually installed with spreaders to help keep the mast straight ("in column"). Temporary guys are also used on a sailboat, a fore-guy is a term for a line (rope) attached to and intended to control the free end of a spar. On a modern sloop-rigged sailboat with a symmetric spinnaker, the spinnaker pole is the spar most commonly controlled by one or more guys.

Utility pole guy-wires

Utility poles are buried in the ground and have sufficient strength to stand on their own; guys are only needed on some poles to support unbalanced lateral loads due to the utility wires attached to them or to resist ground movement. Guys are particularly needed on dead-end (anchor) poles, where a long straight section of wire line ends, or angles off in another direction. To protect the public against faults that might allow the cable to become electrified, utility guy cables usually either have a ceramic strain insulator ("Johnny ball"), or a fiberglass guy strain insulator inserted near the top, to ensure that any dangerous voltages do not reach the lower end of the wire accessible to the public. The lower end where the cable enters the ground is often encased in a length of yellow plastic reflector to make it more visible, so that people or vehicles do not run into it.

In urban areas where the ground area around the pole is restricted, a variation called a sidewalk guy is often used. In this type the guy line extends diagonally from the top of the pole to a horizontal spar brace extending out from the middle of the pole, and from this it continues vertically to the ground. Thus the bottom part of the guy is vertical and does not obstruct headroom, so a sidewalk can pass between the pole and the guy.

An alternative to guy-wires sometimes used on dead-end poles is a push-brace pole, a second pole set at an angle in the ground which butts diagonally against the side of the vertical pole.

Antenna mast guy-wires

Electromagnetic fields from the antennas complicate the design of guys that support mast antennas. Conductive metal guy-wires whose lengths are near to quarter wavelength multiples of the transmitted frequency can distort the radiation pattern of the antenna. This also applies to guy wires of neighboring masts or metal structures situated nearby. To prevent this, each guy wire is divided by strain insulators into multiple sections, each segment non-resonant at the transmitted wavelength. Cylindrical or egg-shaped porcelain "Johnny ball" insulators (also called "egg insulators") are usually used. Non-conductive guys of Kevlar fiber (Phillystran) or extruded fiberglass rod are frequently used to not disturb the radiation pattern of the antennas. The strength and low stretch properties of Kevlar fiber approaches that of steel. However, Kevlar is very susceptible to ultraviolet degradation so it is enclosed in a UV resistant plastic sheath.

The individual sections of conductive guys can develop large charges of static electricity, especially on very tall masts. The voltage caused by this static electricity can be several times larger than that generated by the transmitter. In order to avoid dangerous and unpredictable discharges, the insulators must be designed to withstand this high voltage, which results at tall masts in over-dimensioned backstage insulators. At each backstage insulator, a lightning arrestor in the form of an arc gap is required for the purpose of over-voltage protection in case of lightning strikes. The insulators and arrestors must be maintained carefully, because an insulator failure can result in a mast collapse. Egg insulators have the porcelain in compression and if it fails, the end loops of the guy wires are still intertwined.

Cylindrical strain insulator of type used on utility pole and antenna mast guys. Johnny ball strain insulator.JPG
Cylindrical strain insulator of type used on utility pole and antenna mast guys.

AM radio broadcast towers are often fitted with insulators at the mast base and the RF energy is fed at that point. Some are also insulated at the center for feeding the RF energy at that point. Wire rope guys are frequently used and segmented with insulators at several points. Extensive lightning protection is required for insulated towers.

On antennas for long-wave and VLF, the guys may serve an electrical function, either for capacitive lengthing of the mast or for feeding the mast with the radiation power. In these cases, the guys are fixed without an insulator on the mast, but there is at least one insulator in the guy if necessary. If guys are used for feeding the mast with high frequency power it is often possible to use a grounded mast. The power to the guys is fed via wires running from a tuning unit to the feed point on the guys.

Crane tag lines

When operating a crane, guy wires, known as tag lines, may be connected to unwieldy payloads, allowing ground crew to control rotation and swaying while maintaining a safe distance.

Firefighting

Guys can be used to raise an extension ladder in a technique called a church raise.

Anchors

In ground-anchored guys, the structure which attaches the guy-wire to the ground is called an anchor . [1] The anchor must be adequate to resist the maximum tensile load of the guy wires; both the dead load of the tension of the wire and the maximum possible live load due to wind. Since the guy wire exerts its force at an angle, the anchor has both vertical and lateral (horizontal) forces on it. The anchor relies on the lateral shear strength of the soil to resist the forces from all of the guys attached to it. Several types of anchor are used:

Dead man anchors

Concrete dead man anchor for radio tower guy lines in Britain Guyed mast anchor.JPG
Concrete dead man anchor for radio tower guy lines in Britain

In this type, a hole is excavated and an object with a large surface area is placed in it with the guy wire attached, and the hole is backfilled with earth or concrete. [1] In the historical form of dead man anchor, a log is buried horizontally in a trench with the guy attached perpendicularly to its center. Modern forms are the plate anchor, in which the guy is attached to a rod with an eyelet extending from the center of a steel plate buried diagonally, perpendicular to the angle of the guy. In the concrete anchor, a diagonal rod with an eyelet extending in the guy direction is cemented into a hole filled with steel reinforced concrete. A sufficiently massive concrete block on the surface of the ground can also be used as a dead man.

Screw anchors

This type consists of a rod with wide screw blades on the end and an eyelet on the other for the guy wire. It is screwed deep into the ground, at the same angle as the guy, by a truck-mounted drill machine. These are commonly used as guy anchors for utility poles since they are quick to install with a truck mounted hydraulic powered auger drive.

Expanding anchors

A rod with a pivoted blade on the end is driven into the earth. [1] When the guy wire is attached and tensioned, its force pulls the blade open, "setting" it into the soil. These are often used by the military for rapid mast installations.

Grouted anchors

These are used in both soil and rock. [1] A hole is drilled at the angle of the guy. A steel anchor rod with an eye is inserted, and the hole around it is filled with a liquid grout consisting of concrete and an expansion agent or a structural epoxy. When the grout hardens or expands, the anchor is secure.

Guyed structures

Historically, guyed structures have been some of the tallest man-made structures in the world. There are also many structures which consist of a free standing bottom and a guyed top. These are either partially guyed towers or additionally guyed towers, the latter of which may be used temporarily to support tall buildings during their construction.

See also

Related Research Articles

Insulator (electricity) Material that does not conduct an electric current

An electrical insulator is a material in which the electron does not flow freely or the atom of the insulator have tightly bound electrons whose internal electric charges do not flow freely; very little electric current will flow through it under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors. The most common examples are non-metals.

Warsaw radio mast former radio mast in Poland

The Warsaw Radio Mast was a telecommunications tower located near the town of Gąbin, central Poland, and the world's tallest structure at 646.38 metres (2,120.7 ft) from 1974 until its collapse on 8 August 1991. It was the second tallest structure ever built, being surpassed as the tallest by the Burj Khalifa tower in the United Arab Emirates, completed in 2009.

Whip antenna type of radio antenna

A whip antenna is an antenna consisting of a straight flexible wire or rod. The bottom end of the whip is connected to the radio receiver or transmitter. The antenna is designed to be flexible so that it does not break easily, and the name is derived from the whip-like motion that it exhibits when disturbed. Whip antennas for portable radios are often made of a series of interlocking telescoping metal tubes, so they can be retracted when not in use. Longer ones, made for mounting on vehicles and structures, are made of a flexible fiberglass rod around a wire core and can be up to 35 ft long. The length of the whip antenna is determined by the wavelength of the radio waves it is used with. The most common type is the quarter-wave whip, which is approximately one-quarter of a wavelength long. Whips are the most common type of monopole antenna, and are used in the higher frequency HF, VHF and UHF radio bands. They are widely used as the antennas for hand-held radios, cordless phones, walkie-talkies, FM radios, boom boxes, and Wi-Fi enabled devices, and are attached to vehicles as the antennas for car radios and two-way radios for wheeled vehicles and for aircraft. Larger versions mounted on roofs, balconies and radio masts are used as base station antennas for amateur radio and police, fire, ambulance, taxi, and other vehicle dispatchers.

Transmission tower Structure used to support an overhead power line

A transmission tower or power tower is a tall structure, usually a steel lattice tower, used to support an overhead power line.

Guyed mast Tall thin vertical structure that is supported by guy lines

A guyed mast is a tall thin vertical structure that depends on guy lines for stability. The mast itself has the compressive strength to support its own weight, but does not have the shear strength to stand unsupported, and requires guy lines to resist lateral forces such as wind loads and keep it upright. Guy lines are diagonal tensioned cables attached to the ground, usually spaced at equal angles about the structure's base.

Derrick

A derrick is a lifting device composed at minimum of one guyed mast, as in a gin pole, which may be articulated over a load by adjusting its guys. Most derricks have at least two components, either a guyed mast or self-supporting tower, and a boom hinged at its base to provide articulation, as in a stiffleg derrick.

Dead-end tower

A dead-end tower is a fully self-supporting structure used in construction of overhead power lines. A dead-end transmission tower uses horizontal strain insulators at the end of conductors. Dead-end towers may be used at a substation as a transition to a "slack span" entering the equipment, when the circuit changes to a buried cable, when a transmission line changes direction by more than a few degrees, or just once in a while to limit the extent of a catastrophic collapse.

Utility pole Post used by public utilities to support overhead wires and related equipment

A utility pole is a column or post used to support overhead power lines and various other public utilities, such as electrical cable, fiber optic cable, and related equipment such as transformers and street lights. It can be referred to as a transmission pole, telephone pole, telecommunication pole, power pole, hydro pole, telegraph pole, or telegraph post, depending on its application. A Stobie pole is a multi-purpose pole made of two steel joists held apart by a slab of concrete in the middle, generally found in South Australia.

Overhead power line Above-ground structure for bulk transfer and distribution of electricity

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 suspended by towers or poles.

Blaw-Knox tower

The Blaw-Knox company was a manufacturer of steel structures and construction equipment based in Pittsburgh, Pennsylvania. The company is today best known for its radio towers, most of which were constructed during the 1930s in the United States. Although Blaw-Knox built many kinds of towers, the term Blaw-Knox tower usually refers to the company's unusual "diamond cantilever" design, which is stabilized by guy wires attached only at the vertical center of the mast, where its cross-section is widest. During the 1930s AM radio broadcasting stations adopted single mast radiator antennas, and the Blaw-Knox design was the first type used. A 1942 advertisement claims that 70% of all radio towers in the United States at the time were built by Blaw-Knox.

Radio masts and towers Tall structure designed to support antennas

Radio masts and towers are typically tall structures designed to support antennas for telecommunications and broadcasting, including television. There are two main types: guyed and self-supporting structures. They are among the tallest human-made structures. Masts are often named after the broadcasting organizations that originally built them or currently use them.

Mast radiator Radio antenna consisting of a vertical mast in which the mast structure is energized and functions as the antenna

A mast radiator is a radio mast or tower in which the metal structure itself is energized and functions as an antenna. This design, first used widely in the 1930s, is commonly used for transmitting antennas operating at low frequencies, in the LF and MF bands, in particular those used for AM radio broadcasting stations. The conductive steel mast is electrically connected to the transmitter. Its base is usually mounted on a nonconductive support to insulate it from the ground. A mast radiator is a form of monopole antenna.

T-antenna

A T-antenna, T-aerial, flat-top antenna, top-hat antenna, or (capacitively) top-loaded antenna is a monopole radio antenna with transverse capacitive loading wires attached to its top. T-antennas are typically used in the VLF, LF, MF, and shortwave bands, and are widely used as transmitting antennas for amateur radio stations, and long wave and medium wave AM broadcasting stations. They can also be used as receiving antennas for shortwave listening.

Monopole antenna type of radio antenna

A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the lower end of the monopole and the ground plane. One side of the antenna feedline is attached to the lower end of the monopole, and the other side is attached to the ground plane, which is often the Earth. This contrasts with a dipole antenna which consists of two identical rod conductors, with the signal from the transmitter applied between the two halves of the antenna.

Folded unipole antenna

The folded unipole antenna is a type of monopole antenna; it consists of a vertical metal rod or mast mounted over a conductive surface called a ground plane. The mast is surrounded by a "skirt" of vertical wires electrically attached to the top of the mast. The skirt wires are connected by a metal ring at the bottom and the feed line is connected between the bottom of the wires and ground.

An umbrella antenna is a capacitively top-loaded wire monopole antenna, consisting in most cases of a mast fed at the ground end, to which a number of radial wires are connected at the top, sloping downwards. They are used as transmitting antennas below 1 MHz, in the MF, LF and particularly the VLF bands, at frequencies sufficiently low that it is impractical or infeasible to build a full size quarter-wave monopole antenna. The outer end of each radial wire, sloping down from the top of the antenna, is connected by an insulator to a supporting rope or (usually) insulated cable anchored to the ground; the radial wires can also support the mast as guy wires. The radial wires make the antenna look like the frame of a giant umbrella – without the cloth – hence the name.

Strain insulator

A strain insulator is an electrical insulator 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 antennas and overhead power lines. 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 systems in the mid 19th century.

Austin transformer

An Austin ring transformer is a special type of isolation transformer used for providing power to the aircraft warning lights and other devices on a mast radiator antenna insulated from ground. In the Austin transformer the primary and secondary windings are separated by an air gap, so that the high voltage on the mast cannot get into the low voltage lighting supply wiring, causing safety hazards. It is named after its inventor, Arthur O. Austin, who graduated from Stanford University in 1903 and who obtained 225 patents in his career.

Earth anchor

An earth anchor is a device designed to support structures, most commonly used in geotechnical and construction applications. Also known as a ground anchor, percussion driven earth anchor or mechanical anchor, it may be impact driven into the ground or run in spirally, depending on its design and intended force-resistance characteristics.

In radio systems, many different antenna types are used with specialized properties for particular applications. Antennas can be classified in various ways. The list below groups together antennas under common operating principles, following the way antennas are classified in many engineering textbooks.

References

  1. 1 2 3 4 American Society of Civil Engineers, Subcommittee on Guyed Transmission Structures (1997). Design of Guyed Electrical Transmission Structures. USA: ASCE Publications. pp. 21–25. ISBN   0784402841.Cite has empty unknown parameter: |coauthors= (help)