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Pulling electric wirePulling overhead conductor |
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Electric
supply trailer Trailer carries hardware needed to install electric lines Resource pdf: electric-conductor-grips.pdf power-line-surge-arrestor-DF.pdf Utility-Wire-and-Cable.pdf water-meters.pdf Overhead-wire-types.pdf arc-protective-clothing.pdf power-line-tools.pdf Jumper-clamps.pdf Composite-insulators.pdf Power-line-tool-catelog.pdf Lineman-slang-dictionary.pdf |
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4-drum
Puller Puller sits back away from freeway Pre-assembled 2x8 wood deck is laid to prevent sinking in the mud after frequent rains In the south Texas region, wood decks are used by oil seismic crews etc, and construction of all types Wet soil is also low resistance to ground... the wood deck adds measure of safety for me working with electric cable Dense clay soils as shown here are also less resistant to ground. The less resistance the ground has, the greater conductivity. Less resistance is good for grounding each pole, but damp dense salty soils also make the risk higher for construction cranes working on new freeway. The potential field that develop around an electricified machine is much broader and more more dangerous over wider area. 4 ropes ... each rope attached to a spool The ratio of the distance to the first structure and the height to the first stringing sheave should be three to one (3:1) Correct tension must be kept on the wire during pulling so the wire is not damaged Tensioner is located on other side of highway,,, and keeps correct tension on the wire as it is being pulled across... too little tension and the line drops... too much tension and the line can splay (the cable strands spread apart) Resource Overhead installation guide |
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Puller Puller has 4 spools of rope. Rope is run up to sheaves (pulleys) on the pole, and then over to wires on other pole. Ropes are tied to wires on other pole. Puller pulls the ropes and wire from pole to pole |
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Puller and two poles: Each pole is on opposite side of freeway With 4 ropes ... ropes start at the puller, ... and then up to sheaves (pulleys) mounted on the pole. ... then the ropes lay across live high voltage wires in this instance. ... freeway is closed briefly early Sunday morning ... men run the ropes across the highway. .. they tie ropes onto wires. ... the wire on other side are on 4 spools. ... there are 3 large Hot wires and 1 smaller Neutral wire ... puller pulls the rope and wire back across the freeway ... over the top of the hot wires . ... the men secure new wires to insulators on the pole. .. both sides of freeway are finished.. 2 minutes ... freeway open few minutes later ... wire cannot be left in the sheaves longer than 24 hours or it can damage the conductor .. ... the puller and wire must be |
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Ropes, pole and cable blocks or sheaves (pulley) | ||||||
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Sheave
or cable block attached to pole 4 sheaves are attached to side of pole The ropes loop over the sheaves The width of the sheave is based on the width of the wire. The sheave cannot be too narrow that it damages the shape of the wire |
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Pole on
other side 4 sheaves are attached to side of pole The wires loop over the sheaves, waiting for the rope to be tied. Once the rope is tied to wire, the puller brings the wire across the freeway. The tensioner is located on other side of freeway. Tensioner makes sure there is not too much slack in the wire, not too tight that the puller bends the wire. A shield has been added over the top of live hot wires on other side, in event a wire drops from above |
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Neutral
/ static wire and hot wire The power company is installing 3 Hot wires and 1 Neutral wire. This is required for distribution of electric power When the Neutral wire is located on top of pole, it is also called a static wire. Static wire is defense against lightning strike, and catches the excess voltage and redirects it to ground. Neutral is always smaller than Hot wire. One reason is economy. Wire size and material is a balance of cost and performance For example, copper wire might be a better conductor for transmission and distribution... ... but copper wire is too expensive, and too heavy and too soft for long spans between poles. Aluminum-covered steel wire is strong and relatively inexpensive, and it performs the job, so it is better choice than copper. Resource: 3-phase electric: power plant to end user |
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Aluminum
wire and aluminum-alloy steel wire Freshly cut wire has dislodged some of the strands.... strands are splayed open This design of stranded wire is called concentric round, since each strand is the identical, each is round, and cable is round. Air space between strands can be reduced by compacting aluminum into trapezoidal shape for smaller wire size. This is example of #600 aluminum wire. The number of strands on wire in photo is 37, and .775" in diameter. Overhead wire can have 70-127 strands and 2.3" or more in diameter, and made from a variety of aluminum alloys. Household wire can be 7-19 strands and less than 1/4" across Wire size and material is a balance of cost and performance For example, copper wire might be a better conductor for transmission and distribution... ... but copper wire is too expensive, and too soft for long spans between poles. Aluminum wire is relatively inexpensive, and it performs the job equal to copper, so it is better choice than copper. Zinc coated and aluminum coated steel wire is used where temperatures exceed 200° F Resource pdf: Ampacities-of-overhead-conductor Overhead-Installation-Guide 4_overhead_conductors Mechanical-Design-of-Overhead-Lines Advanced-Conductors-for-Overhead-Transmission Design-overhead-distribution overhead_conductors1 Overhead-aluminum-conductor |
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Conductor
examples Different conductors are chosen for different applications Illustration is general depiction of materials and not exact numbers of strands or types of cores or shapes of wire configuration. Choice of conductor is always a balance of electrical efficiency and cost of materials Galvanized steel wire surrounded by aluminum wire is used for long spans. ACSR ACAR Steel wire is strong, but a poor conductor. The aluminum wire carries most of the electricity. The 'skin effect' causes most of the current to flow close to the surface of the wire. The wire that is pulled across the freeway on this job is #795 steel core surrounded by aluminum, 37 strand, .89" diameter For shorter spans, up to 50 meters, with high load demand, all-aluminum wire is used. AAC AAAC For rural areas with few customers, price of conductor becomes important issue. Galvanized wire is often used. Galvanized steel is a poor choice of conductor for areas with high load Overhead conductors can last at least 40 years Resource Types of overhead conductor |
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Hot
wires on this distribution line are .775"
in diameter Looking at power lines while standing on the ground, they look small. But up close, they are large, heavy-duty wires... These particular wires are on a distribution line serving several neighborhoods, sewer treatment facility, cell phone towers, and small businesses including fast food, gas stations, a small assembly plant etc. |
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Hot wires Each transmission and distribution pole has 3 hot wires and one neutral |
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.774"
diameter wire The key head is 1-1/16"/ 37-strand aluminum overhead conductor |
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Wire
ties and wire Wire ties are used to attach the wire to the insulator at each pole. Wire ties are prefabricated for each wire size Rubber insulator is inserted on the wire or on the tie to prevent wire from touching insulator. Insulators are made from variety of materials including glass. When viewing electric repair trucks and supply trailers on the road, you can see the pre-fabricated ties hanging on back of vehicle |
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Next
day: New overhead conductors across freeway The line tension and sag must be calculated. Wind load, ice load, expansion caused by temperature, clearance above road, elongation-over-time, age, number of hours exposure to loads.... each is a factor. This installation in South Texas is subject to hurricane force winds, 50 miles from the coast. Each wire has a rating based on maximum conductor strength when energized Resource: Conductors for overhead transmission wires |
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Hot from
North side of freeway attaches to South side Suspension clamp is tightened against wire using 4 bolts. Wire is bent downward. The bend in wire adds a mechanical resistance to slippage of wire The bend also pulls the Hot wire away from the insulator. The Hot wire is connected to Hot wire on pole. Suspension clamp is connected to insulator. Insulator is bolted to steel pole Long suspension spans use aluminum-coated steel wire or steel cored aluminum ACSR Aluminum wire will sag more than steel wire over long spans. Steel coated aluminum wire is used. The steel carries mechanical strength while aluminum strands carry bulk of current Poor conductivity of steel makes it a poor choice for long distance transmission of high voltage. Galvanized steel is used in rural areas with few customers on the line because it is less expensive. |
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Insulators Strain and suspension insulators are same ... when installed to carry horizontal load, they're called strain, and when insulator hangs down to carry a load below, it's called suspension. Photograph taken in Houston Texas during construction of new towers. The old tower was being dismantled and wires disconnected. The insulators we about 6' long, and connection for wires indicated 2" conductor. |
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Neutral connection at top of pole :Neutral from pole north of freeway, tied to Neutral line on south pole using 2 compression fittings Neutral connected to top cap insulator using side tie |
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| Additional wiring | |||||||
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Electric
supply trailer carries additional rolls of wire Various sizes of wire for installation at homes and businesses. The supply trailer is used each day for variety of jobs. For example there is a length of triples wire that is used for home installation and repair |
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Distribution
pole assembled on ground Poles are delivered without hardware, and dropped in location where each will be set Linemen install hardware on each pole Each type of pole is assembled to specification. For example the polymer riser (insulator) must be set at specific distance from bottom of pole, and from each other. The distance from polymer riser to pole is specified. The number and location of guy wires. The size and application of ground wire. Wood poles are used for spans up to 50 meters. Wood poles rot underground after 20-25 years Generally not used for voltages higher than 20 Kv Resource: Mechanical design of overhead power |
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Distribution pole assembled on ground | ||||||
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Top of power pole A shackle insulator has been added to pole. This is a type of strain insulator that lets linemen install a short line to another pole for local service |
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Guy wire connection | ||||||
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Power
pole tool: Cant Hook Linemen use ordinary tools: drill, wrench, stapler They also use specialized tools such as the tool shown (cant hook) that is made specifically to roll the pole, or keep it from rolling. They use climbing spikes and safety belt when ascending and descending pole. |
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Cant Hook | ||||||
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Standoff
for ground wire Extra length of ground wire looped back in toward the pole will be attached to Neutral wire at top of pole |
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Standoff
for ground wire Each wooden pole on the distribution grid has a ground wire that travels down the side of pole. Standoffs are used to keep the ground wire away from hot wires And help prevent possible arcing from the hot to metal parts on the pole and then to ground. Once the ground is below the height of the hot wires, the ground wire is attached directly to pole. Bottom of pole, the ground wire enters the soil Resource: 3-phase electric Household electric service Why you need ground Formulas-for-Ohms-law |
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Standoff for ground wire with ground wire attached Extra wire will be connected to Neutral wire at top of pole |
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Neutral
compression connection to ground wire Every pole has a ground wire. The ground wire always connects to Neutral Then the ground wire runs down side of pole to the soil when a ground connection is made Each ground is based on type of pole, height, location, type of soil etc Neutral wire runs from pole to pole across the entire grid. Ground wire is connected to neutral using a compression coupling. before installation, both conductors are cleaned with wire brush and coated with inhibitor |
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Ground
wire runs full length of pole. Here is the connection point between the copper ground wire and the aluminum-coated steel wire that runs to top of pole On some pole, the copper wire is used for full length of ground. In this instance, the aluminum-coated steel or aluminum wire is used since it is cheaper. The bare copper wire is #6. Copper can never be installed above the aluminum to prevent copper salts from washing down on aluminum. |
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Ground
at bottom of power pole: Butt coil Depth of pole into ground is determined by engineers during planning stage Once the pole is set in the soil, the weight of pole helps the ground make contact with soil Using a coil of wire on the the bottom or butt of the pole is common technique. Using a butt plate is another method. A butt coil is made from the #6 copper wire that is stapled to side of pole. The copper wire is coiled on the bottom, and pieces cross each other to maximize contact. In addition to the coil, a ground rod is also driven into the soil to depth that is specified by engineer. Depth of ground rod is based on resistivity and dampness of soil. The ground must reach soil that is permanently damp... and below the frost line This installation is done in a damp Texas coastal region with clay soil. Dense soil such as clay has less resistance to ground than dry rocky soil. The best soils are dense, non-frozen, clay. The worse soils are loosely compacted gravel with a permafrost. Grounding specifications vary by soil, type of pole, voltage, etc. Resource: Why you need ground |
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Ground wire | ||||||
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Ground
wire runs full length of pole Neutral wire from top of pole is connected to copper ground wire near bottom of pole. A ground wire can come off the Neutral at any point. Purpose of the ground wire is to provide safe earthing of any overvoltage. Purpose of the Neutral wire is to connect all Neutral together across the grid back to the main generator. The purpose of the Neutral-ground system is to connect all grounds together into one array of earth connection that will absorb overvoltages, protect against lightning, assist circuit breakers, and stabilize the electric grid.... basically 'balance the equation.' CAUTION... a ground wire might be energized... touching or disconnecting the ground is extreme danger. This applies to power line at distribution pole, transmission towers, and ground connections in your home.. Resource: Why you need ground |
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| Connect electric wire to insulator | |||||||
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Top cap Top cap is one type of insulator used to keep wire away from pole. Wire can be attached to top of cap, or on side Top cap is type of insulator used to keep wire from touching the pole Insulators are required to withstand mechanical and electrical stress. Electrical stress is caused by line voltage... failure is caused by a crack or puncture and flashover. Higher voltage/ the greater the cost of insulator Over 33Kv, a suspension insulator is used instead of a pin type insulator Resource: Mechanical design of overhead power |
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Top cap and side tie Top cap sitting on disturbed soil near freeway construction. Prefabricated tie partially om the cap Tie has rubber insulator to hold wire away from insulator |
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Wire,
side tie, top cap. Same image as above, photoshopped. with photo of Neutral wire |
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Connect
electric wire to insulator Simulation of connection using photoshop. The tie wire is wrapped 1 turn around cap Rubber insulator forms a barrier between wire and cap Tie is twisted around the wire. |
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Neutral
connection Compare with images above: Neutral from pole north of freeway, tied to Neutral line on south pole using 2 compression fittings Neutral connected to top cap insulator using side tie |
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 Contactors/ relays |
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