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Described as the "largest most complex machine ever built,"
this page covers commonly visible parts and functioning of the electric grid from generation to end user.
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Names of parts on electric pole Described as the "largest most complex machine ever built," this page covers commonly visible parts and functioning of the electric grid from generation to end user. |
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Lineman's Books Practical application and terminology/ not mathematical Buy from my affiliate links Lineman's electric book Overhead conductor Understanding Bonding and grounding Understanding National Electric code Wiring Simplified Wiring a House Power generation by Singh 3-phase power generation book Electric Power generation books Home wiring books |
 Larger image Another image with coal pile Night image of WA Parish Power plants are rated by megawatt MW output, or 1000 kW or 1,000,000 watts (watts = power) or 1,000,000 VA (volt x amps = watts or power). 1 MW can supply power to 400-600 homes. Or 200 homes on hot summer day, since air conditioners (loads) are pulling more amperage, but also because high heat reduces the amp-carrying capacity of power lines, transformers, solar panels etc. How much amperage does house use Amp rating of power lines A gigawatt GW is 1 billion watts = 1000 megawatts of power What is power factor Power factor and solar Up to 5% of a conventional power plant (synchronous ac rotating machine) generation can be used to operate plant .... to power the electromagnet, to run the pumps needed to circulate water used for cooling, etc. Resource: Power-Plants.pdf The 3,653 Megawatt WA Parish power plant site read more has coal fired (steam) generation where burning coal is used to boil water into steam using a boiler, and the steam explosion is used to accelerate a turbine that spins an electromagnet located inside a generator. Thermal efficiency or megawatt thermal rating of coal generation is about 33% ... with 67% 'waste' heat that can be used as heat source etc. Read See image of coal plant Image of large heat pump water heater Parts for coal plant .pdf WA Parrish also has gas fired generation (as secondary fuel) where burning gas accelerates a turbine that spins the generator. Gas generation has fewer emissions than coal (when methane releases are not considered read), and is considered "quickest to sync and reach full load for daily and seasonal intermittence," and uses "less water per megawatt-hour generated than coal-fired counterparts.'' Emission chart Power plant types .pdf Advancements have shown that coal generation can also be responsive to intermittence (including the unpredictable on-and-off of renewable generation). Note that stop and
start operation (ramp-up and turndown)
reduces efficiency per MW of power, increases maintenance, and shortens
life of turbines, generators, bearings etc as metals expand and
contract with the heat caused by operation. Manufacturers are improving
this aspect where possible.
Thermal generation from coal, atomic power ... oil, NG, LNG, LPG, hydrogen, gasified coal, ethanol, syngas, biodiesel, alcohol, kerosene, steel mill gasses, etc image ... plus hydroelectric installations ... accelerate a turbine ... and the turbine rotates the generator to produce electricity. Read more |
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 Larger imageAnother image Another image Another image Another image Steam turbines are designed for various uses, including to spin a generator to produce electricity. How it works: Water is boiled into steam using coal, atomic power, exhaust from gas turbine etc. The steam explosion releases massive energy that is used to rotate the turbine, and turbine spins generator. Read more Read more https://www.powermag.com/ |
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 Larger imageAnother image Another image Trailer-mounted turbine and generator Gas turbine aero-derivative gas turbines Single-cycle turbine. Simple-cycle gas turbine SCGT. Read Gas turbines are designed for many uses, including to spin a generator to produce electricity. The gas turbine is basically a jet engine. How it works: Filtered air is sucked into the compressor and fed into the combustor where expanding gasses from ignited fuel cause the turbine to rotate at high speed. Gas turbines rotate at 3600 rpm (for 60 Hz markets) or 3000 rpm (for 50 Hz) are made for wide variety of generating capacities, ranging from 35,800 hp to 345,600 hp, and are regulated for NOx emissions, with 30-40% thermal or fuel efficiency. Source Manufacturers are working to reduce CO2 emissions, for example by making turbines adaptable to burn hydrogen, biofuels etc, and injecting amounts of water into the combustion where it produces a mini steam explosion etc, helping to accelerate turbine without using gas. Too much water will cause cooling and loss of power. Single-cycle
turbines are typically used for peaking generation and
to compliment intermittent generation from renewables, skewing the
overall efficiency and CO2 production attributed to renewables. Peaking
plants come online fast to meet shortfalls, and then turn down when
demand spike ends.
"Efficiency of a turbine at part load can be substantially below the
30-40% efficiency at full-power," while continual stops and starts
degrade a turbine more rapidly ... causing more non-recoverable losses and
more maintenance to repair recoverable losses. Gas turbine failure modes .pdf
Read advancements in turbomachinery
Combined gas and steam (COGAS) Combined cycle gas turbine (CCGT) Designed for continual operation or baseline power generation. Advances have produced the economical Combined Cycle Power Plant where 800-1,000°F exhaust heat from one or more gas turbines (topping cycle) is recaptured and used to boil water into steam (heat recovery steam generator HRSG). The steam is used to heat buildings etc, or to rotate a steam turbine (bottoming cycle) that spins a 2nd generator (double-shaft configuration image) ... or to run a shared generator (single-shaft configuration image). A combined cycle, with both gas and steam working together, can have 50-63% thermal efficiency, depending on ambient air temperature, contaminants in air, humidity, elevation, fuel type, age of turbine, condition, degradation etc. Image Image Video: combined gas and steam Video combined cycle Chart with cost comparison Thermal efficiency is
not same as total efficiency.
"Total efficiency is defined as the sum of the net electricity
generated divided by total fuel input to the system." Total efficiency
is lower percent than thermal efficiency depending on factors such as
degradation of equipment, temperature, humidity, type of fuel,
start-and-stop losses, transformer losses, electricity used
for cooling pumps and electromagnet etc..
Gas turbines and gas engines (shown below), etc are designed to operate 25-30 years or more, so the capability of burning multiple fuels gives 'flexibility to continue operating plant (with hydrogen, ammonia, synthetic methane, gasified coal, methane releases from old coal mines etc), even in a decarbonized world.' .... Siemens is planning to make all their turbines capable of burning hydrogen (and other available gasses) since hydrogen produces no CO2, and is absolutely clean fuel while "electrolysers that produce hydrogen has risen greatly read Cummins pdf, and the cost of renewable electricity to power those electrolysers is falling." IEA 2021 Cummins, manufacturer of engines etc, suggests that hydrogen will be better allocated to run vehicles and not for generating electricity. Resource: Manual |
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 Larger imageReciprocating gas engine This is a massive and very loud V18 cylinder piston engine with approx 40% efficiency. Also called, simply, gas engine. The gas engine is often used to power ocean-going vessels, and can be used to spin a generator to produce AC electricity. The gas engine can be set up to recapture and reuse exhaust heat, improving efficiency. Like gas turbines shown above, the piston engine can come online quickly (20 minutes) from a cold start to meet intermittence from renewables, can be repaired to help maintain efficiency, and are usually designed to burn different types of gasses, including the methane content of natural gas. |
 Larger imageLarger image Another image Another image Generators come in different sizes depending on requirement. Generators produce AC electricity. They can be water cooled, air cooled, hydrogen cooled etc ... made to be powered by gas or steam turbines etc, ... made with different MW output ... available for 50 Hz or 60 HZ (hertz, cycles, frequency, or number of back-n-forth oscillations per second of electrons in alternating current) depending on country. The Siemens generator shown in image above is spun by gas turbine seen in background. The large size of generator plus listing by Siemens as 26,000 volt suggest this generator is for continuous baseline generation, and not intended for fast ramp up and turn down to compliment intermittent renewables. Generally, generators run with 96-99% efficiency, and are repairable. For example, the central stem or rotor of a generator can be replaced along with bearings etc to provide longer life and updating. .  |
 Generating alternating currentThe grid delivers alternating current (AC) to homes and businesses. Solar and wind generation must be converted into same voltage and frequency AC power before being dispatched to the grid. All appliances, computers etc are rated for AC power as shown on product label. ''At the center of nearly all conventional (coal, oil, gas, atomic, hydro) power stations is a generator, a rotating machine that converts mechanical energy into electrical energy by creating relative motion between a magnetic field (north and south pole magnet) and a conductor (coils A B C).'' In general, with coal, oil, gases, atomic, hydro powered generators, the electromagnet inside generator spins past 3 coils (or windings) of wire that are spaced exactly 120° apart inside the generator. Or more exactly, the rotor rotates inside a stationary stator, like a large electric motor. See image of hydroelectric generator Video Resource pdf Another resource .pdf Alternating current: As the electromagnet passes each coil, the coil becomes energized with a pulse of electric power that reverses each time the north and south poles pass. Back and forth, the electrons race down the coil and out onto a wire, momentarily stop and then race back the other direction, creating what is called alternating current. While voltage rises and falls with the momentary halt and reversal of electrons, the action happens so fast that the average voltage is always above zero and functions as a level voltage. Frequency The electrons make a complete cycle, there and back, 60 times per second in the Americas and 50 times per second in rest of world. This is called Hz, hertz, frequency, or cycles. Frequency is monitored closely so multiple power plants (solar, coal, gas, hydro, wind etc) can safely dispatch along the same transmission line without damaging generators, equipment etc, and so end users receive stable, predictable power. Target range for 60 Hz power is 60.1 Hz and 59.9 Hz. 3-phase transmission: 3 Hot wires and a Neutral leave the generator: A wire is connected to one end of each of the 3 coils, and those 3 wires leave the power plant and become the 3 Hot wires found in 3-phase power that is transmitted across the grid. Each of the 3 Hot wires is called a phase. The other ends of the 3 coils are joined together to form the Neutral wire that travels with the Hot wires, and is bonded to the ground rod array located under the power plant and switchyard, and is bonded to a ground at each tower, pole, substation, and installation along the way. See image The 3 Hot phase conductors and Neutral are electromagnetically coupled at the generator, thus helping the Neutral wire act as a shield against lightning, reducing magnitude of surge, as long as Neutral is grounded at each pole. 4-wire, 3-phase with 3 hot wires and a neutral is most efficient method for transmitting electric power. Out of phase: Energizing the Load: Since the generator magnet passes each coil at a different moment, each Hot wire carries electrons that are 'out of phase' with electrons on the other Hot wires, and also out of phase with the Neutral. When out of phase wires are connected to a load, the electrons oscillate back n forth between each wire, going back and forth through the load and energizing the load. |
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 BatteriesStorage of power via batteries, and power generators of all type, have 2 basic measures: Energy capacity or how much power is generated or stored, and Power capacity or amount of power that can be dispatched or released to grid.. Types of Batteries 'The success of renewables is reliant on long-duration energy storage' using electrochemical batteries (BESS battery energy storage systems), pumped hydro (PSH), compressed air (CAES), hydrogen fuel production etc. Read Read Cars, motors, machines etc can use flywheels (FES) to store energy. Gravity batteries (mechanical battery) can be used inside skyscrapers etc. Storage comparison by type 2020 Note that storage of hot water at each home etc is example of thermal energy storage (TES). Connect AC water heater to low voltage DC Connect AC water heater to high voltage DC Electrochemical batteries According to EIA in 2021, the US has '1.6 GW of utility-scale electrochemical battery capacity that is expected to increase 4-fold by 2022.' Image Battery manufacturing has increased worldwide as technology works to develop higher density materials (including solid state batteries) that will deliver lower cost per kilowatt hour at same time the world strains to provide enough minerals (and food, water etc). Read Peak electric
consumption (maximum usage on hottest day) in US in 2020 was about 800
GW per hour,
and expected to increase with economic growth, government mandates for
'all-electric' homes and buildings, plus manufacturing goals for
electric vehicles, higher global temperatures etc.
Using 2021 for
example, the 1.6 GW energy capacity of electrochemical batteries in US
would equal .2% of total power needed for 1 hour of
800 GW peak, or equal to .12 minutes of electric consumption before all
battery capacity would be depleted. Calculation Afterwards,
batteries would need to be re-charged before dispatching another 7.2
seconds out of a 24 hour day. If battery construction could be afforded
and sustained 1000 fold, to 1600 GW, it would supply 120 minutes, or 2
hours of a peak day in the US. Usage of power is less than
peak most days, but continually growing.
Compare MW rating of gas turbine vs batteries For example compare 50 MW gas turbine generator vs 50 MW battery installation. Both appear to offer same power, but the gas turbine generator has a much higher power capacity and can deliver 50 MW of continuous electric power, 24 hours a day. While a 50 MW battery installation can deliver 50 MW once and then must be re-charged. Note that neither source would be clocked-out at maximum, nor have 100% efficiency. Batteries are not designed to power the entire grid Batteries can be charging and discharging throughout day as renewable output varies. They can respond quickly to "balance momentary differences between electricity demand and supply, and frequency." They can be used to store power for later in day when prices are favorable. Typically, batteries are used to level (smooth) intermittent dispatch and avoid curtailments of solar panel generation due to solar causing irregular grid frequency etc. battery-applications.pdf What is power factor Power factor and solar "Overall, batteries are expected to help utilities avoid need for load shedding." Source Battery limitations Electrochemical batteries (both Flow or long flow batteries and higher density Lithium Ion or Li-io) have high efficiency, and are good at keeping grid frequency stable, but are expensive (all costs are energy). Read Lithium Ion batteries discharge in 1-4 hours, are prone to catching fire or starting fire, cannot be installed in fire area, have finite lifespan (5-15 years), have power drop-off with higher elevation and at temps over 104°F, with steep decline as temperatures rise, and total loss at 131°F image from GE. Note also that power cannot be stored indefinitely inside a battery. Read Read more |
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 RenewablesPie chart image on right shows worldwide electric production 5 months of 2021, and comes from OECD In 2021, renewables (Hydro, wind, solar) generated about 29% of world production, while Fossil Energy (FE) generates 53%, and nuclear contributes 17%. Image Image Image Image Wind, solar and hydroelectric rely on weather to produce electricity. Weather is unpredictable, making it a poor choice to meet reliability goals, if intent is to supply power to all users ... particularly since batteries cannot energize the grid nor meet current usage nor sustain growing demand. Renewables are experiencing a building boom as costs, media promotion, investors seeking long-term pay-out and science push government and business toward the “sustainable development scenario” (SDS) outlined by IEA. Forecasts show that challenges are present: Chart Article Read |
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 Nuclear power is reliable and has been used for decades to generate electricity and to propel military ships and submarines.Advancements in lower-cost small nuclear reactor (SMR/ producing <320MW) and microreactor technologies .... for example GE Hitachi BWRX that does not require electric pumps, or X-energy mobile reactor for the military, or X-energy's 320-MWe Xe100, or Westinghouse AP1000 AP300 with no moving parts, or thorium reactors etc, ... are being deployed and/or developed to provide '24/7 carbon free' baseline power. Read Read Read "Renewable energy supplemented by nuclear is cheaper than renewable supplemented by long-term battery storage." Nuclear is statistically safe, but has disadvantages. Nuclear requires water for many designs, some designs can continue generating power after shut-down, and the threat of nuclear waste is real, but the threat of CO2 is here, while nuclear waste (SNF) is generally considered a threat in several hundred or thousand years. Read | |
| Reliability and jobs Unlike wind and solar (inverter-based) generation that must be changed into matching voltage and frequency as conventional thermal generation. the coal, nuclear, hydroelectric, and gas turbine plants require large number of employees to keep plant operational, including welders, trainloads of coal, bulldozer operators, gas pipelines etc. Few workers are needed once solar and wind farms are established and connected to grid. Job losses from
closing coal and other thermal generation plants etc are offset by
growing need for workers to upgrade and automate the grid,
upgrade substations and distribution, with better energy forecasts,
improved batteries, etc, plus build new transmission lines to keep up
with the building boom in solar and wind.
However, as demand increases, and the grid becomes more complex, and increasing amounts of intermittent renewables and DERs and microgrids come on-line, the challenge shifts to grid reliability ... specifically to maintain stable frequency and keep voltage "within ±10% of nominal at all points across the grid." Keep in mind the grid is cris-crossed over millions of square miles, with millions of poles and transformers and customers ... comprising a system that might not be fully mapped at the local distribution level in 2021. Read The grid must hold voltage steady/ Load shedding Power (wattage) is equal to volts x amps. Voltage is the force that pushes amperage or current of electrons across the wire. By design, in normal conditions, average voltage remains level while amperage rises and falls, with more amperage flowing when more loads are turned on. Even though power plants are interconnected, each power plant can only energize a certain distance or area. If several power plants go offline, or demand exceeds supply, or main transmission lines suffer cascade of failures etc, then power must be shut off (load shed) to some customers so voltage levels can be maintained for remaining customers. Video 2003 failure Video 2021 Texas failure In a simplified version of events that ignores the role of frequency etc, if voltage drops
below nominal, then your 115 volt refrigerator and 240 volt AC cannot
run without damaging the motor.
Why? Two reasons. 1) Lower volts reduces the magnetic field needed to spin rotor. Motor slows down and overheats. 2) Volts and amps are inversely proportional. If volts drop, then loads will draw more amps to meet the amount of watts (power) shown on product label. Wires are rated by amperage, and are generally not oversized (larger wire carries more amperage but costs more). Exceeding the amp rating means too many electrons are moving through the matrix (atomic structure) of the conductor (wire), causing more resistance from wire which causes heat which overheats design parameters of wires, motors etc... affecting substation relays that will trip off ... and can affect power plant generators that will automatically shut down to avoid damage. |
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 Larger image Another image Another image Image shows Vertical transmission structures or Steel lattice towers with .. with switchyard and coal-fired power plant in background. "The switchyard delivers generated power from the plant to the nearest grid or transmission line.'' The lines shown in this picture are estimated to carry 220,000+ volts (220kV) en route to Houston and surrounding area. EHV or extra high voltage, is roughly defined as 345,000– 765,000 Volts. UHV or ultra high voltage is > 800,000 volts. HVDC or high voltage DC 100,000+ VDC is 'more efficient for long distance transmission over 300 miles' because lower line loss, but requires costly converter stations to change DC (direct current) into AC (alternating current). Image Multiple power plants (of any type: solar, coal, gas, etc) can be connected to a single transmission line via substations, and each source of power must deliver same voltage, and each helps hold voltage steady along full length of line. Result is wide area is supplied power at specified voltage level. The plant includes "generator step up transformers, grounding transformers, substation buses, main substation transformers, tie lines and points of interconnection." Resources: Transmission-Structures.pdf Transmission-Structures-811.pdf Difference-between-single-phase-and-3-phase.html |
 Larger imageOriginal image Helical Rod Spacers hold the double-bundled wires apart from each other while stabilizing the lines. Double bundled wires are a simple way to transmit twice the power, and are typically found on higher voltage transmission lines Parts needed for transmission, such as insulators, wire, bolts, assemblies etc are rated by voltage and strength. Resources: Overhead-Installation-Guide.pdf Mechanical design of overhead power lines Hubbell suspension support .pdf |
 Larger imageAnother image Power line corridor Another image 3-phase transmission ''Transmission structures support the phase conductors and shield wires of a transmission line.'' (Phase conductors are Hot wires and shield wire is the Neutral). -Power lines and towers are designed to withstand load factors such as heat, ice and high wind. Image shows Vertical transmission structure which is one type of 'Steel lattice tower 'Steel lattice towers (vs wooden and concrete) are used for the highest voltages.'' It takes 3 wires for a 3-phase line or 3-phase circuit. "Towers can carry one or more circuits, depending on the design (e.g., single-circuit vs. double-circuit towers)." Image above shows a double-circuit tower. "For voltages up to 200 kV, a phase is typically a single conductor (3 wires total per circuit). For voltages over 200 kV, bundled conductors are often used to increase the current, or amp carrying capability of the line and reduce power loss caused by heat. Bundled conductors consist of two or more conductor cables connected by spacers. 220-kV and 500-kV (220,000 and 500,000 volt) lines often have two conductors per phase (6 wires total per circuit).'' Source Transmission-Components-Fact-Sheet.pdf |
 Larger imageExample single circuit, horizontal configuration, self-supported lattice tower w/ approximate dimensions Illustration shows a single-circuit transmission with 3 bundles of hot wire or phase conductors that are suspended 119' above ground. Building a horizontal lattice tower is 'cheaper than building Vertical transmission structures' shown above, but horizontal can be limited to a single circuit, while vertical towers carry 2 circuits. Each conductor bundle is suspended 32' away from other bundles using an assembly with V-string suspension insulators. Insulators hang downward when power lines travel straight forward (suspension insulator) .... or are installed horizontal when power lines make a turn or come to deadend (strain insulator). The steel towers are flexible and bend with loading. Problems can occur if footings sink unevenly. Concrete and steel poles are being used more often today for transmission since they are more attractive than lattice towers, except poles are limited by their ground line moment ... reference the amount of force that causes them to break. Lattice towers are stronger than and more versatile than single poles. Power line design is done via computer program today, unlike earlier times when designs were calculated for each tower. Source with more terminology Transmission-Structures.pdf Resources Cost comparison transmission towers Cost comparison transmission construction |
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3-phase
Transmission Vibration dampers are added to each line as it nears a suspension point. Dampers are used to reduce line movement caused by wind loading. Note that parts and assembly are done by men using tools. Building, repairing and updating the grid is labor intensive, so each part must be carefully engineered and then installed correctly to ensure decades of service. Other protections include armor rods installed where the wire is held by the suspension clamp. ''ARMOR RODS are designed to protect cable against bending, compression, abrasion, and flash-over. They are also used to repair damaged aluminum-based conductors and restore the conductors' mechanical strength and conductivity.'' Resource: Vibration dampers Hubbell damper-armor rods-line-protection.pdf Armor rods .pdf Transmission line repair manual |
 2 Conductor Horizontal I-String Materials for power line assemblies vary by need and include: Polymer, Toughened Glass Galvanized Forged Steel, Steel, Galvanized Ductile Iron, Aluminum, Aluminum Alloy Larger image |
3-phase
Transmission Suspending dual wires from transmission tower Image shows Assembly for suspending a two conductor bundle from a transmission tower. The dual wires are held 18" apart using two suspension clamps attached to a yoke plate. Transmission wires are protected from damage using armor rods and vibration dampers. The assembly is designed to move and sway with wind load encountered by all overhead electrical installations. Resources: Hubbell damper-armor-rods-line protection.pdf Hubbell-suspension-clamps.pdf Hubbell-suspension-assemblies.pdf Hubble yoke plates Transmission connectors .pdf MPS_transmission-catalog-web.pdf |
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Note that parts require a
man or men to
install and tighten
bolts. Suspension clamp 3-phase transmission Overhead conductors are exposed to wind and other conditions that can damage the wire. To prevent damage, utilities install vibration dampers, armor rods, and in this example, a suspension clamp with helical cushion to absorb movement while protecting the wire. ''Suspension clamp with helical cushion is designed to provide enhanced conductor support and protection." "The rubber inserts are assembled directly onto the conductor and are held in place with the helical rods. The clamp assembly is then bolted around the helical wrapped rubber supporting inserts to compete the install.'' |
| Parts Ball eye, ball clevis, socket eye, socket tongue, socket clevis, socket thimble, anchor shackle, twisted shackle, Anchor shackle, Bow shackle, Chain, and D Shackles, twisted strap, clevis eye, eye chain link, chain link, clevis tongue, extension link, U-bolt, adjusting plate, yoke plate, turnbuckle  Pole-and-Line-Hardware.pdfSuspension clamps .pdf Transmission connectors .pdf Power-pole-parts-and-specifications.pdf Suspension clamp U
bolt type
Strain clampsPreformed armor grip suspension clamp Strain clamp for ACSR, AAAC, steel wire Hydraulic compression type Deadend bolted type |
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 Larger image Another image of corona rings/ estimated 500,000 Volt Another image/ estimated 500,000 volt tower "Unlike ceramic insulators, polymer insulators have relatively shorter life." |
3-phase
Transmission Corona ring/ Corona shield For HV high voltage >220kV ".. corona ring or corona shield is used at the HV end fitting for improving the electric field and potential distributions and then for minimizing the corona discharges'... protecting insulators from corona degradation. 2006 Corona-effects.pdf' Hubble corona rings pdf Note that wires, suspension clamps and end fitting are all electrified up to beginning of insulator. Electrified parts create electric field that can jump or arc to nearby objects. The insulator is designed to stop elecrtricty from arcing or shorting to steel pole. When polymer insulators are "exposed to intense electric fields, insulation failure and loss of hydrophobicity (ie water should not be able to penetrate surface of insulator) may occur." "These problems are caused due to non-uniform electric field distribution along the insulator, which tends to intensify the electric field on the sheds nearest to the phase terminal (connection of conductor and insulator). Non-uniform electric field distribution can be minimized using suitable (correct design, size, and placement) corona rings." |
 There
are "36 different shed profiles for composite insulators. There
are four
categories for the 36 profiles depending on number of different shed
diameters within each
unit: .... Category 1.) alternating one large and one small;
2.) one
large, two small; 3.) one large, one medium and two small; and 4.) one
large, one medium and four small." |
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3-phase
Transmission Vertical Bundle Suspension. Larger image  |
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Larger image 3-phase Transmission Vertical Bundle Suspension on newly rebuilt transmission line. Image shows 6 hot wires (or phase conductors) in 2-wire bundles, making this a single-circuit transmission line with 6 Hot wires and one Neutral wire at top of pole where it is called a shield wire because it shields the power line from lightning strike damage. Hot wires can be bundled in twos, threes or fours to increase the amp-carrying capacity of the circuit. Polymer line post insulators support wire and insulate it away from pole. The 3 line post insulators are aeach ttached to a metal base that is bolted into the side of a spun concrete pole. Each base is connected to the ground wire that starts at the Neutral wire at top of pole and terminates at a ground rod located at bottom of pole. Image of ground connection |
 Larger imageOriginal image Another image 3-phase Transmission Horizontal line post insulator made of fiberglass compound with silicone polymer sheds attaches to spun concrete pole with a base fitting or gain that is made to match diameter of pole. Bundling Yokes are suspended from the line post insulator via a Y-clevis. "Bundling yokes can vary in width, 2-1/2" to 4-1/4" and length 9"-12"-18". Image shows 18" Armor rods are installed to protect wires at the point of suspension. The double-bundle wire and lack of corona ring suggest that voltage is at or near 220kV. Resource: Line post insulators pdf Each spun concrete pole has a nameplate with specifications such as weight, height, serial number etc. See ''Prestressed (or spun) concrete poles are more durable than wood or steel poles and more aesthetically pleasing." "The reinforcing inside concrete poles consists of (a) spiral wire cage to prevent longitudinal cracks and (b) high strength longitudinal strands for prestressing. The pole is spun during manufacturing to achieve adequate concrete compaction and dense smooth finish. A concrete pole typically utilizes a high strength concrete. Standard concrete poles are limited by their ground line moment capacity (breaking off at ground level). Concrete poles are much heavier than steel or wood poles. Their greater weight increases transportation and handling costs. Thus, concrete poles are used most cost-effectively when there is a manufacturing plant near project site.'' Each spun concrete pole has an embedded label showing weight, height, date of manufacture, serial number etc. Example |
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| Porcelain insulator vs silicone rubber insulator | |
 Larger imageOriginal image 3-phase transmission Steel tower near downtown Houston lays on the ground after being replaced with concrete poles. Each porcelain suspension disc is designed for voltage rating 11KV or 11,000 volts each disc. Insulator voltage range can be from 10KV to 1000KV. Image shows two sets of dual porcelain strain insulators, each string about 8' long. "A porcelain insulator consists of a number of porcelain discs connected in series by metal links in the form of a string. Insulators are assembled with other metal parts to provide the means for non-rigidly supporting electric conductors." Insulator types Note the flexibility of the string, to absorb effect of wind on the conductors (hot wires). Larger image The steel towers were replaced by concrete poles, and porcelain insulators were replaced by newer type, lighter weight composite or polymer insulators. Toughened-glass-insulator.pdf Failure-of-High-Voltage-Porcelain-Insulators.pdf |
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Insulators
can be divided into two types: the heavier, more expensive,
longer-lasting porcelain
insulator vs newer type, lighter weight, cheaper silicon
rubber insulator." "Polymeric composite insulators consisting of core fiber reinforced polymer insulators covered with polydimethylsiloxane (PDMS) housing are now replacing conventional ceramic insulators especially for high-voltage outdoor (above ground) power transmission lines due to specific advantages," and so "more countries are choosing the silicone rubber insulator vs porcelain." Advantages-polymer-vs-ceramic-insulators.pdf Resources: Porcelain-Suspension-and-Struts.pdf Orient-suspension-insulator-definition.pdf Toughened-glass-insulator.pdf 2018 Degradation-and-stability-polymer-insulators.pdf 2006/ polymer-vs-glass-insulator.pdf |
 1991,
LAPP insulatorsTwo men connect flexible porcelain insulator to a rigid strut insulator Note weight of insulator with 16 porcelain discs. The connectors are installed as much as possible while the pole is on the ground before pole is lifted in place. 2021, many installations and upgrades today use less expensive, lighter weight polymer insulators. Note that the grid requires strong, skilled men who perform the same high risk installation, pole after pole, until project is complete. While the poles, parts and wire can be manufactured by computers and robots, the actual field installation requires a labor force that can assemble parts to specification. The grid is put together with nuts and bolts that are tightened by men. Source Porcelain-Suspension-and-Struts.pdf |
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 |
High
voltage tools Buy: High voltage tools Electrician tools kits Klein tools Tools kits |
| Neutral/ Shield and Grounding and lightning | |
| Dead end towers are
used where a transmission line ends; where the transmission line turns
at a large angle; on each side of a major crossing such as a large
river, highway, or large valley; or at intervals along straight
segments to provide additional support. A dead-end tower differs from a
suspension tower in that it is built to be stronger, often has a wider
base, and has stronger insulator strings." Source "Dead-end towers are used where a transmission line ends; on each side of a major crossing such as a large river, highway, or large valley; or at intervals along straight segments to provide additional support ...or where the transmission line turns at a large angle (as shown in pictures below). A dead-end tower differs from a suspension tower in that it is built to be stronger, often has a wider base, and has stronger insulator strings." Source Other types of structures include Tangent, small angle, large angle, strain, plus deadend Source  Larger image Stafford Texas  Larger image Another-image |
3-phase 2-circuit
Transmission/ Neutral
and Grounding The grid carries 3-phase power that is delivered via groups of 3 hot wires (phase conductors) that are accompanied by the Neutral. The Neutral wire is visible at the top of the steel tower where it is bonded (connected to) the steel tower and subsequently to the ground or earth. The wire at top each pole or tower goes by different names and has different functions. It is called a static wire because it is bonded to the grounding rod located at bottom of each pole, and will discharge the build-up of static charge that occurs naturally in the environment. For transmission towers, the line is called the ground in most resources because it is bonded to the ground rod, giving a low resistance pathway to earth.\ It is called a shield wire or shieldwire because it 'shields' or protects the grid from lightning strike by deflecting the energy at downward angle away from the phase conductors, at same time it directs excess charge into the ground rod. A shielded line is vital for grid reliability. For consistency and simplicity, this website (perhaps erroneously) refers to the wire at top of both transmission towers and distribution poles as a Neutral wire. At the end user location, the distribution pole carries a Neutral that is needed for many commercial 3-phase transformer configurations and voltages, and needed for many single-phase household and commercial voltages. Across the entire grid, the Neutral (or static wire, shield wire) is bonded to the ground at each tower, pole, substation, and user location. This forms a giant array of grounding that stabilizes the grid from lightning and overvoltages that are safely absorbed into the earth to minimize damage. "Due to its magnetic coupling with the phase conductors, a periodically grounded wire reduces the magnitude of surges induced by nearby strokes and may improve the lightning performance of a distribution line." |
 Another
imageAnother image Another image Electricity is often described as a flow of charged particles between unequally charged materials. Insulating materials including air will stop the flow of particles until the charge becomes great enough to overcome the insulation. When different temperature air masses collide, the opposing movement of air (or shear) can strip lighter-weight, negatively-charged electrons away from heavier-weight, positively-charged protons, causing pockets of charged particles to gather in the clouds. Each pocket carries a charge that is 'unequal' with the charge on the ground. read The result is a buildup of electrical potential to the point where the flow of particles (positive or negative read) will pass through the insulating effect of air via a cloud-to-ground lightning bolt. The lightning will often strike highest point like a tree, hilltop, or power line, releasing massive electric power. The shield wire or static wire or system neutral located at the top of transmission and distribution poles etc is directly bonded to a ground wire or rod, that is driven into the earth. This ground wire gives the lightning a low resistance path to earth thus reducing damage to poles, conductors, transformers etc.  The amount of lightning per area of a storm is generally referred to as the Ground Flash Density. If the lightning carries more energy than the ground wire can absorb, there can be a flashover onto the conductors, or hot wires. The flashover can cause substation breakers and relays to activate and shut down the line. To prevent this, areas that experience frequent thunderstorms and high flash density might need arresters that protect insulators from 'lightning induced flashover.' Image Resource: Porcelain-Suspension-and-Struts.pdf Failure-of-High-Voltage-Porcelain-Insulators.pdf |
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| Transmission vs Subtransmission vs Distribution | |
 Larger imageAnother image Electric poles transformers folder Rosenberg Texas 3 categories of power lines: Transmission-level voltages are usually considered to be 110 kV and above. Lower voltages such as 66 kV and 33 kV are usually considered sub-transmission voltages. Voltages less than 33 kV are usually used for distribution. 1) Transmission lines (not shown in image) might be 270,000 to 500,000 (775-500-270 kV) volts. Generally transmission is anything over 115 kV. Voltages are measured Hot-to-Hot, also called the line voltage ... contrast with Hot-to-Ground phase voltage which is line voltage divided by square root 3. Read 2) Subtransmission lines might be 69,000 Volts (110-69-33 kV), and travel from substation to local substation and are located higher off the ground than local distribution lines. Transmission and subtransmission make up the bulk power system. 3) Distribution lines travel from local substation to each home and business, and are much lower to the ground and carry less dangerous 12000+ volt, measured between hot wire to hot wire ... and 7200 volts (7.2 Kv) measured between hot wire to ground. "The distribution voltage classes for most utilities can be 5 kV, 15 kV, 25 kV, and 35 kV." Voltages are determined at local substation transformer and vary depending on local demand, distances etc. |
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 Note
that the commercial three-phase
transformer bank
is connected to the distribution lines, drawing a hot wire from each of
the 3 lines, with each transformer also connected to the Neutral wire.
The distribution transformers then supply power to local
business. Identify WYE or Delta on
commercial transformer banksThis is called 3-phase electric service. Distribution Transformers are required at each end-user location to convert high voltage distribution power into usable, safer, low voltage for homes and business. Because volts and amps are inversely proportional (when volts are reduced, then amps are increased), the safer lower voltage at home and business comes with higher amps. To solve problem of heat caused by higher amperage, correctly-sized wire and circuit breakers are required, and distance electricity can travel before voltage falls below nominal can be limited to a few hundred feet. See inside residential breaker box Because of the volt-amp difference, each home and business only draws a small number of amps off the distribution line. For example a 250 amp residential service with 250 amp main breaker. Suppose the home is drawing maximum 250 amp, it will only draw 8 amps off the 7200 volt distribution line. See calculation Since most homes are not drawing maximum amperage, each home might be drawing 1-4 amps off the distribution line. Transformers are used throughout the grid to raise and lower voltage. Distribution transformers located at each home and business are always connected to distribution lines, not to subtransmission or transmission lines. Distribution lines always come from a power transformer located at local substation, and never connect directly to higher voltage subtransmission. Likewise subtransmission lines do not connect directly to higher voltage transmission, but instead come from substation transformers. Local distribution lines can be less than a mile to more than 20 miles long. There are generally 3 categories for distribution: Radial, Loop, & Network (not discussed further). Resource: Design-overhead-distribution.pdf Mechanical design overhead lines pdf Electric-power-distribution-system-operation.pdf |
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| Upgrading subtransmission vs limited capacity of Wood poles | |
 Image shows wood pole with
single-circuit subtransmission with 3 hot wires and
1 neutralLarger image Original image Wood poles and crossarms are made from yellow pine, cedar, and spruce ... with yellow pine being the strongest. Wooden structures are economical to install vs steel and concrete poles, but are not as sturdy against load factors such as high wind and generally have shorter lifespan. Wood poles can carry single circuit subtransmission (with 3 or 6 hot wires and a neutral) 69KV, 115KV, 138KV, 161KV, 239KV ... but not carry higher voltages of 345KV and 500KV. Wood poles can carry a double circuit (with 12 hot wires and 1-2 neutrals) 69KV and 115KV only .... While steel poles and steel lattice towers can carry single and double circuits of all voltages. Source p12 Steel pole w 3 circuits Image shows porcelain insulators with 7 sections @ approximately 11 Kv each. Multiplying 7 x11 Kv each means the circuit can carry maximum 77 Kv or 77,000 volts, assuming insulators are not degraded from accumulated dirt or pollution, or suffered cracks etc. There is voltage potential between any Hot wire and any other Hot wire, called the line voltage. In this example, the line voltage must be less that 77 Kv, so the next lower standard voltage is 69Kv, 69,000 volts. There is also voltage potential between any Hot wire and the Neutral, called the phase voltage. Line voltage of 69Kv divided by square root 3 = 39.8Kv phase voltage. Read more The single-circuit subtransmission line shown in picture was replaced with heavier, stronger, taller spun concrete poles, and the insulators changed from porcelain-ceramic to less expensive polymer insulators. The 3 hot wires were replaced with larger diameter wires that were double-bundled (giving a single-circuit with 6 hot wires) to achieve higher amp carrying capacity, and the line voltage was increased from 69,000 volts to 200,000+ volts. Why use higher voltage? The grid is a balance of cost and function. Higher volts and lower amps means more force is pushing fewer electrons across the wire. This reduces heat loss and gives higher efficiency and lower cost, but also allows power company to use comparably smaller wires. Wires are rated by amperage, with larger diameter wires capable of carrying more amps. Smaller diameter wires weigh less and can be suspended from poles that are spaced farther apart... which reduces number of poles, cost of materials, and cost of installation. Other methods include, using aluminum conductor (wire) with steel strands inside the core for greater strength that allows longer span between poles, and using trapezoidal shape instead of round strands so conductor diameter is compressed see image... so end fittings are smaller and the conductor is less exposed to stress from sun, wind ice, etc. Note also that 3-phase, or the use of 3 wires per circuit, allows more amperage to flow along smaller wires vs single-phase that uses 2 wires instead of 3. This is the reason why 3-phase is more efficient for delivering power to end users and for running commercial motors etc than single-phase. Resources: Difference 3-phase and single-phase Cost comparison transmission construction .pdf |
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| Substation | |
 Larger imageAnother image 3-phase high voltage Power transformer at local substation Different voltages are achieved using transformers located at substations. High voltage transmission lines never touch or connect directly to subtransmission lines. Instead, they are connected via isolation-type power transformer located at a substation. Likewise, the subtransmission lines and lower voltage distribution lines are isolated from each other via substation transformers. For example, high-voltage transmission and subtransmission lines supply power to local substations where one or more power transformers convert high voltage into lower voltage distribution lines that carry around 12,470 volts. Distribution lines or circuits are the local power lines that are connected to 'telephone' poles and travel along streets going to local homes and businesses. The large cylindrical tank mounted on left side of power transformer contains oil for cooling the transformer. The upright insulators located on top of transformer are called bushings. Ordinarily, average voltage remains relatively unchanged throughout the day, while amperage (or number of electrons flowing along the line) rises and falls depending on the load, with more amps flowing when more loads are turned on. During high consumption periods, or peaks, the voltage is pushing massive numbers of electrons across wires and through the transformers. The increased flow of electrons encounters increasing resistance which acts like friction, causing heat across the grid. Transformers are rated by their KVA (power) capacity, and how much heat they can withstand, but also how fast they recover (cool) after a high-heat or peak event. Resource Recommended-losses for-power-transformers.pdf Large-Power-Transformers and-the-Grid.pdf Substations have voltage regulators (often built into transformers). So if transmission lines deliver voltage above or below standard voltage, the regulator will correct outgoing distribution voltage so local area will not suffer voltage irregularities. Read more |
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 Larger imageAnother image Another image 3-phase distribution Many poles leave substation transformers, traveling to each business and neighborhood Wires leaving a local substation branch off many directions on wooden poles, sending power to local homes and businesses. This is the source of 12,000 volt distribution. Follow power lines using google earth to reveal complexity of transmission and distribution networks. Poles leaving substation carry groups of 3-wires, always accompanied by Neutral. Distribution poles are generally wood, but can be steel or concrete, especially where wires are suspended across roads. Each pole has ground wire running down pole and into the ground. "Distribution substations contain many components, a few of which are power transformers, circuit breakers, and voltage regulators. The power transformers step down sub-transmission voltages (69 kV to 125 kV) to distribution voltages (2.4 kV to 19.92 kV). Circuit breakers, that shut down power during overloads on the line, are placed between the distribution circuits and low-voltage bus for substation protection during fault or surge conditions. Voltage regulators are installed on each distribution circuit if the power transformers are not equipped with automatic tap changing capabilities that enable bus voltage regulation.'' Source P13 Voltages generally stay the same across the incoming high voltage lines, but momentary surges can occur. Voltage regulators and tap changers automatically react to anomalies so that distribution voltage going to local homes and businesses remains stable, and doesn't experience the same surge. |
| Local distribution lines/ wood poles/ underground vs above ground | |
 Larger imageAnother image Newly installed 3-phase 12,000+ volt distribution lines Air is the insulation This newly installed overhead distribution line has 7/8" diameter bare aluminum-alloy wire. The shine is not photoshopped, it is reflected sunlight in late afternoon on new aluminum wire before it has weathered and oxidized. Overhead wires are bare and have no insulation. Wooden poles have good insulating properties, and generally last 25 years before they are rotted beneath the ground and need replacement. Note that poles are not set into concrete since concrete holds in moisture which accelerates rot and reduces insulation properties. To ensure power does not arc to ground or other structures, high voltage wires are suspended in the air, using the air as insulator. The higher the voltage, the higher the wires are suspended to ensure safety. The pin type insulators on each pole keep bare wires away from poles and other wires. Insulators must have high mechanical strength to withstand loads such as wind and have high electrical resistance. 'Porcelain is most common material for this type insulator, but glass, steatite and other composite materials are used. Pin type insulators are used up to 11 kV (11,000 volts)' www.woodpoles.org Bare overhead wires are cheaper to install but don't last as long as insulated underground cables. Underground transformer vaults can be susceptible to flooding and water damage. Hubbell-underground-vaults.pdf |
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 Larger
imageAnother image Another image Another image Overhead vs underground The grid is a balance of cost and function. "Overhead line construction is less expensive (3x to 10x less expensive) than underground cabling for the same kVA (power) load. In rural or semi-rural areas, the sheer cost of underground cabling would make it impossible for customers to afford cost of supply. The downside is that overhead lines operate under continual mechanical stress with exposure to varying climatic conditions (wind, heat, ice, lightning etc). This results in progressive deterioration in time as a result of corrosion, mechanical wear and fatigue, timber rot, etc. All components must be periodically inspected and replaced" However overhead lines are easier to inspect for damage, and are rarely damaged by short-term overloads and catastrophic failures are rare." "Overhead systems are rarely as reliable as underground ones. The greater spacing of overhead line conductors generally results in higher system inductance (resistance over time) than for a cable system. This means an overhead line has a greater voltage drop than an underground cable of equal current-carrying capacity and hence cannot supply power over as long a distance as the underground equivalent. However the capacity of an overhead feeder can be readily increased by replacing it with larger conductors and/or increasing the voltage level. This flexibility is one big advantage of overhead systems." Source P18 Wood-distribution-pole-Design.pdf www.woodpoles.org Let's
suppose, if all homes in a neighborhood install solar panels. In
Hawaii, it was determined that just 50% of homes feeding PV-generated
power back to the grid on a good day posed problems that required
updating distribution lines and substation transformers. If a
neighborhood has underground distribution lines, then updating for
rooftop solar would be more expensive than above-ground distribution.
In this example, the cost of distribution improvements should be
included when calculating the value of rooftop solar.
Line
sag.
'Bare overhead conductors are able to withstand a lot of pressure and
high temperatures,' but lines will sag if they are carrying too many
amps (current of electrons), even if lines are thermally rated to
handle emergency loading. Lines usually have "thermal time constraints
that allow temporary overloading (5-20 minutes)," but if the problem is
not cleared quickly, then sagging lines can come into contact with
trees or with each other, causing outages. High currents can also cause
conductors "to anneal, which increases chance of a break happening. |
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| The grid/ Power plant switchyard to home | |
 Larger image of whole gridIn a simplified version of events, the illustration shows grid transmission from power plant to home. Homes and businesses require high-amp, low-volt power. The problem is high amperage causes heat loss during long-distance transmission. To resolve, transformers located at substations can raise and lower amps by raising and lowering voltage. Voltage and amperage are inversely proportional. When volts are reduced at substation transformer, then amps are increased. The result is low-amp 500,000 volt electricity is used for long-distance transmission. Higher amp, 69,000 volt subtransmission lines are used for shorter distances. And higher amp 12,000 volt lines are used for local distribution. For example, transformers at local substation reduce 69,000 volt subtransmission lines into safer 12,000 volts so it can be distributed along wires that are suspended nearer to ground and can pass close to trees. Residential single phase is achieved by taking one 7200 volt Hot wire (measured Hot to neutral) and a Neutral off the 3-phase 12,000 volt (measured hot to hot) distribution line to create 7200 volt single phase. The single 7200 volt Hot wire and Neutral are then connected to each of the residential transformers in the same neighborhood. |
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 Larger imageOriginal image Converting 12,000+ volt 3-phase lines into 7200 volt single phase ... pulling 1 Hot and a Neutral off distribution lines. When measured across 2 Hot wires, the line voltage is 12,000+ volts. When measured from any Hot to the Neutral, the phase voltage is 7,200. One Hot wire and the Neutral are used to supply power to neighborhood. Once the 7200 volt Hot and Neutral reach each home, the residential transformer will reduce the 7200 volt single phase into usable 120-240 volt single phase (also called split phase), ensuring that households receive safe, low volt, high amp power. Numerous homes will draw amperage off the same 7200 volt power line without overtaxing the line. That's because a 250 amp 120-240 volt residential service that is running at full capacity will pull a maximum 8 amps off the 7200 volt distribution line. Since few homes will be running at maximum, most will draw just a couple amps off the power line. Resources See calculation Ampacities of power lines Low volt, high-amp power works nicely because household 120-240 volt single-phase can be safely controlled by small switches, relays, cell phone chargers etc contained within steel and plastic enclosures, while the amperage (and heat) is controlled by circuit breakers (overcurrent protection) and then distributed to outlets, switches, clothes dryer etc using correctly sized wire to match amp rating of breaker. Resources: Line-post-insulators-Insulators.pdf See inside residential main breaker box Grounding 3-phase |
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| Larger image 3-phase 12,000+ volt distribution lines supply power to single-phase and 3-phase services Typical 3-phase distribution line follows alongside a road or street, and supplies both 3-phase and single-phase for all end users located along the way. Note the three phase service for the sewer station has 3 transformers, and it requires 4 wires to energize the 3 transformers .. pulling 3 Hot wires plus the Neutral off the distribution line, while each single-phase service for homes has 1 transformer, requiring 1 Hot and the Neutral. The same distribution line can supply power to multiple neighborhoods with each neighborhood pulling off a separate Hot wire in effort to keep the 3-wire 3-phase distribution lines 'balanced.' Balanced mean all 3 hot wires on the 3-phase distribution line will supply the same amount of power, and that one hot wire does not do more work than other two hot wires. Identify 3-phase transformer wiring |
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| Lightning
and Shield wire Refer to photo above: Note the nearest pole has a 4x4 extension at top of pole to hold the Neutral wire ... also called the static wire, static line, shield wire .., and sometimes called the ground. The Neutral at top of pole is always bonded to the ground rod or grounding located at bottom of each pole. When the shield wire is at top of pole as shown, it can protect the 3 hot wires from lightning. It will also protect the communication and internet cables located lower on pole. Older distribution lines might have 3 Hot wires at top of pole with the Neutral traveling below. If there are taller subtransmission lines nearby or taller structures, there is minimal risk. If not, then a line without shield wire is more susceptible to damage from lightning. A damaged phase conductor will run hotter and with less efficiency, sometimes requiring splice repair or line replacement between two poles. Power companies can change older installation by adding a 4x4 and moving Neutral wire to top. Another option is to install a taller pole. The 4x4 technique allows new and old distribution lines to connect at minimum cost ... or keep older pole in service more years. |
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 |
7200
volt distribution Hot clamps are often used to connect smaller lines to a larger conductor or distribution line. When the conductor arrives at home or business, then a hot clamp is used to connect the transformer to the distribution lines. Hot clamps are also used to pull a 7200 volt distribution line off the three phase distribution to supply single phase to a neighborhood. This type clamp is used on 7200 volt distribution lines, but not on high-voltage transmission and subtransmission lines. Resource: Line post-insulator.pdf Hot clamps pdf |
 |
Single-phase
7200
volt distribution Hot clamps For connecting transformers and other wires to a 7200 volt distribution line Note that parts require a man or men to install and tighten bolts. Resource: Hot clamps pdf another image |
 See
LargerSingle-phase 7200 volt distribution line arrives at home Power poles carry high-volt, low-amp electricity -High-volt low-amp lets power company transmit electricity long-distance without heat loss caused by high amperage. Before entering house, electricity is converted to lower volts and higher amps at distribution transformer. Different transformers are used for different voltages. -Residential transformers receive 4500-7200 volts from 1 high voltage line and a neutral. The transformer reduces voltage to 240Volts and splits the voltage into two 'out-of-phase' 120Volt Hot wires that enter home. The two out of phase Hot wires offer 240Volt potential used to power water heaters, air conditioner etc. While 120 volts using 1 Hot and 1 Neutrals used for outlets and lights. -Note: 3 wires enter home <> 2 hot wires and 1 neutral wire <> the neutral also connects to ground wire at bottom of service pole. The ground wire is bonded (connected) to the ground rod that is driven into the soil and is used for safety and to stabilize the grid. Resources: Where power comes from: What is 3 phase Difference between household and commercial electricity Read about electric power from power plant Why you need ground wire |
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| Neutral
connects to transformer. Ground wire connects to Neutral wire. Ground wire is smaller diameter than Neutral. Ground and Neutral work together for household safety, stability of grid, and to help absorb overvoltages and shorts caused by lightning, equipment failure, surges from inductive loads etc. |
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 Single-phase
7200 volt distribution line arrives at homeUnderground residential electric service is same as above-ground service -It's easier to photograph above-ground electric service. -All electric services, above and below ground, follow same pattern from power line => to transformer => to meter box => through the meter => to main breaker box. -Meter and meter box for underground service is the same as above ground, except wires arrive in underground conduit pipe instead of dropping down from a pole. -Transformers for underground service are inside ground-level boxes or underground vaults, and perform exactly same function as above- ground, except offer more protection, reliability and longer lifespan. Resource: Underground electrical vaults .pdf |
 Larger imageOriginal image Single-phase 7200 volt distribution line arrives at home 7200 volt Hot and Neutral wire arrive at home. The Neutral is at top of pole, and Hot wire is suspended lower on pole. The residential transformer converts 7200 volt distribution line into safe 120-240 volt for use inside household. This transformer supplies power to a single home. Power is pulled off the Hot line using a Hot Clamp attached to the Hot line. The fuse protects against overloads and fault currents (amperage). The surge arrestor protects against overvoltage. Both work together to protect the installation. 'Transformers have no moving parts, ensuring a long trouble-free life under normal conditions.' Power leaves the transformer via triplex wire that is attached to side of transformer. Triplex is a 3-wire bundle made up of two insulated Hot wires and a grounded bare aluminum neutral wire that are strong enough to be suspended overhead until they enter a service mast and drop down into t he meter box before entering the household main breaker box. |
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 |
2 Insulated Hot wires and
bare aluminum Neutral wire Resources: Read more about residential transformer Surge arresters .pdf See inside household electricity Basic home electricity Figure volts amps watts |
 Larger imageOriginal image Single-phase 7200 volt distribution line arrives at home Same as above: 7200 volt Hot and Neutral wire arrive at home. The Neutral is at top of pole, and Hot wire is suspended lower on pole. The Neutral atop the pole serves as a shield wire to catch lightning strikes and safely redirect the excess voltage to ground so it will not damage the electric grid. High-strength steel wire for long spans that carry few amps. Resources Overhead grounding standards Grounding code Dead end clamps |
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 Fuse Full image |
Single-phase 7200
volt
distribution
line Fuse cutout located on power pole -High voltage distribution wires carry 4500-7200 volt that must pass through a fuse before connecting to transformer. -Fuse will trip when heat exceeds fuse rating, protecting transformer from surge caused by lightning, overload, malfunctions etc. -Electric company resets fuse using long fiberglass pole. -Far left image shows high voltage line terminating on a porcelain dead end strain insulator located on last pole at end of street. Resource cutout-fuse-instructions.pdf  Larger image |
 Tripped or open fuse Larger image |
 Larger image Larger image  |
7200
volt
distribution
line Dropout fuse/ or Cutout ''The primary function of the drop out expulsion type fuse is to protect equipment connected to distribution overhead lines from overloads and fault currents within its rating.'' This type fuse is used on 7200 volt distribution lines, but never on high-voltage transmission and subtransmission lines. Note that resetting a fuse requires a skilled man and a truck. Resources Cutout-fuse-instructions.pdf Hot sticks and power line tools pdf Fiberglass Hot sticks arc-flash-clothing.pdf power-line-tools.pdf techline-lineman-tool-catalog.pdf Klein-lineman-Tools-Utility-Catalog.pdf Different types of cutouts  Lineman resets fuse at night Larger image The lineman must wear protective clothing and insulated boots. Resetting fuse can result in flash explosion. |
| Static belt
serves as continuous ground/ protection
when
working close to energized lines Conductive suit, hot suit, conductive Boots, socks, gloves / clothing is bonded to the conductor so lineman can use hands on live conductor Rubber insulating gloves must operate within voltage class, must be in good condition for work on hot lines Protective Ground Grid / ground blanket/ for a lineworker to stand on during energized and de-energized work Temporary conductor support fiberglass is used to hold energized distribution conductors during replacement of poles or repair or replacement of pole top and stand-off insulators Temporary Conductor Support: Nylon binder strap ratchet assembly hold energized distribution conductors during replacement of poles or repair Grounding set with grounding clamp each end Resources Hubbell Performed energy Spun concrete poles Lineman slang dictionary Performance-Evaluation-Overhead-Power-Line-Proximity-Warning-Devices pdf Aerial-tools-and-equipment.pdf Distribution repair manual |
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 Larger image Another image |
Single-phase 120-240
volt residential service Resource: See inside household electricity  Larger image Single-phase distribution transformer -After 7200 volt distribution Hot wire travels through the fuse, it drops down to the lightning or surge arrestor, and then connects to the primary bushings located top of the transformer. Note the Neutral wire connects the other bushing on top of transformer, and also connects to ground wire. -The ground wire is bonded to the shell of the transformer, and to any metal that is attached to pole before traveling down length of pole into soil at base. Across the grid, all poles, transformers, and electrical services are grounded, with all grounds bonded to the Neutral, forming a giant array of grounding that stabilizes the grid against overvoltages, lightning and insulation failures etc. -The transformer photo shown above supplies electric service to two homes instead of more typical single home. Disadvantage of serving two homes is lights flicker when heavy amp loads turn on, such as air conditioner. -Electricity leaves the transformer and travels through 3-wire bundles called triplex that contains 2 Hots and 1 Neutral. Distribution transformers .pdf Why-are-transformers-used.html |
 3-phase
arrives at building3-phase 7200 volt distribution line arrives at commercial building Typical 3-phase service has 3 transformers, while single-phase service has 1 transformer. The same distribution lines that supply 7200 volt to neighborhoods and individual homes also supply power to businesses and buildings that require 3-phase service. Single phase power delivered to homes requires one transformer, while a 3-phase service to buildings requires 3 transformers (which are sometimes installed as a single transformer that contains 3 transformers). A service is the voltage and amount of KVa or power that is delivered from the grid to the building. A residential service is 120-240 volt single-phase, while a commercial 3-phase service can be a variety of voltages including 120-208-240-277-480-347-600 volt etc. ''When a building is not of sufficient height, a service riser will be necessary to achieve the proper service drop clearance. When field conditions do not permit the use of a riser, a service pole may be substituted.'' Resources JEA-Overhead-Grounding.pdf Difference between single-phase and 3-phase What is 208 volt What is 277 volt |
 3-phase 7200
volt
distribution
lines arrive at building service
Larger image Original image Another Delta-WYE service Rosenberg Texas 3 phase service at local Walgreen Image shows Delta Primary and WYE Secondary. Primary and Secondary are terms that describe transformer connections, with the primary side connected to high voltage distribution lines and secondary connected to end user, such as Walgreens etc. Delta and WYE are terms that describe how the 3 transformers are wired on the primary and secondary sides. Read more about transformers In this example, the primary is wired as Delta: How do we know? There are 3 hot wires from the distribution line, and each hot wire connects to bushings on two different transformers.... so the three transformers are wired in series or Delta on the primary (or distribution side). With delta wiring, the System neutral does not connect not to the bushings located on top of transformers. In this example, the secondary (or customer side) is wired as WYE. Note that the secondary wires connect to side of transformer, and not to bushing on top of transformer. The secondary has 4 wires: 3 hots and 1 Neutral. The Neutral connects to all three transformers, while each of the 3 Hot wires connect to a different transformer ... so the three transformers are wired in parallel or WYE on the secondary (or customer side). Transformers can be wired different ways depending on the incoming electric supply and end user need. Resources: Transformer configurations pdf Index of transformer manuals Identify more illustrations of transformer wirings Power line surge protectors pdf Read more about 3-phase service What is 208 volt WYE |
|
  Insulated wires attach to secondary
side (customer side) of commercial
transformerImage shows secondary taps on commercial transformer. Bolted connections are more secure than compression. Each installation on the grid requires tools, trucks and men. Each crew is trained for a specific voltage range. So a man working on 12,000 volt distribution will not work on 79,000 volt subtransmission. Higher voltages use different trucks, materials, tools, parts, techniques and safety equipment. Most line work is done with live power, so knowing and following exact technique is necessary for survival, but also longevity of installation. As general rule, linemen are large, strong men who must perform each action and install each part exactly, with bolts torqued to specification so the installation lasts decades without problem. Note how wire size exactly matches the point of attachment on the transformer. |
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 Larger imageOriginal image 3-phase 7200 volt distribution lines arrive at building service High leg delta service at local business Fig-2 shows 3-phase distribution lines coming from across the street on 3 Hot lines and 1 Neutral The Neutral can be seen at the bottom, while 3 Hots are at top. If the Neutral was located at top, then it would act as shield wire to redirect a lightning strike into the ground wire at each pole. Since this installation is un-shielded, then if lightning or surge impacts the Hot wires, the lightning arrestor and fuse will protect transformers. If surge on the Hot wires exceeds rating of wire and fuses, then the breaker at substation will trip and protect the distribution and transmission systems. The distribution Hot wires in this picture are bare, stranded aluminum or aluminum alloy, approximately .5" in diameter, while the wires on the secondary side that go to the customer service panel are always insulated. Wire size and material used for the grid are a balance of cost and function. For example, copper offers less resistance and less expansion and contraction than aluminum but copper will pit and erode outdoors ... steel is very strong and resistant to heat but very heavy ... so aluminum and aluminum alloys are the choice for most overhead electrical conductors because of cost, function, conductivity, abundance, resistance to weather, durability over time etc. Copper is best choice for interior wiring. Why? Safety. Wiring inside homes and businesses carry high amperage. High amperage causes heat. Aluminum wire will expand more than copper when exposed to heat. As a result, aluminum connections expand and contract as loads turn on-off, causing connections to come loose and start to arc (spark), creating high risk of fire unless properly installed with special AL-rated compression fittings. Resources: Types of electric cable pdf What is high leg delta |
 Larger imageOriginal image Rosenberg Texas near fairgrounds 3-phase 7200 volt distribution lines arrive at service 3 phase service at county fuel depot With 3-phase service, there are several different standard voltages and transformer configurations depending on end user need. In this case, the 3 transformers on Primary side are connected in parallel (WYE) since the Neutral wire connects to the Neutral bushing on each transformer. Likewise, the Secondary or customer side is wired in parallel, so this is a 208-120 volt, 480-277 or 600-347 volt WYE-WYE service. Note that the Neutral wire is below the 3 Hot wires. This means the Neutral cannot function as a shield against lightning strike. Since the location had no other tall structures nearby, an unshielded service is more prone to damage since lightning will energize the Hot wire(s), causing potential outage and damage. The fuses and lightning arrestor located on each Hot line and transformer will minimize damage. Resources: What is 3-phase |
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3 phase service drop The image in table above shows the primary and transformers The image to left shows the service drop for the image above. |
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Same service drop as the
image above. Resource: Drop-wire service ends |
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Drop wires and
service ends are standard sizes to reduce number of parts for
installation and repair. Once installed, the installation lasts for decades. Cables and insulation coating are made to high standard to avoid deterioration from heat, cold, ice, wind, repeated expansion and contraction etc. Drop-wire-service-ends.pdf Preformed clamps (also called service ends or informally called wiggle wires) are used to secure insulated conductors, guy wires, neutral wires etc. Preformed clamps come in specific lengths, diameters, strengths etc ... and each has a specific use. |
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 Four
insulated wires drop
down from a 3-phase transformer bank to
a commercial building where they are secured to structure (steel riser)
using service ends or preformed clamps (shown above).To avoid contact with trucks, people etc, a service drop must meet standard height above ground. This service drop uses a steel riser to meet height requirements. Each of the 4 drop wires are split into two wires at the riser, resulting in 8 wires ... 4 wires enter each weatherhead, then drop down through two service masts to the raceway where they split into more lines that travel upward into each safety cut-off en route the 3-phase meter. Each business in the building has separate meter. After leaving the meter, the 3 Hot wires and Neutral travel through conduit and enter the building, where they enter the 3-phase main service panel or circuit breaker box. The steel riser, weatherheads, conduit, meter boxes, safety switches etc are grounded for safety. This is the system ground that can be seen at far right side of raceway, to left of door, where a ground rod passes through concrete parking lot and enters soil. The system ground differs from equipment ground. Inside the breaker box, each circuit has a ground wire that connects to ground busbar. This is the equipment ground. Electric services are labor-intensive, requiring certified electricians, electrical engineers, inspectors, high-quality parts, etc, plus years of experience investigating cause of electric fires etc. |
| Overhead switch | |
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imageOverhead switch/ Sectionalizer/ Break Switch 3-phase 7200 volt distribution lines >"Sectionalizers are one of the most used for distribution system protection. The sectionalizer opens and isolates the faulty section of line. This permits the power company to re-establish supply to those areas free of faults. If the fault is temporary, the operating mechanism of the sectionalizer is reset." Overhead switch lets power company de-energize lines for repair and emergency A metal pole with a manual switch lever is located at bottom of pole When switch is open the line on one side or the other is de-energized. Resource: 4 Factors To Consider When Selecting a Sectionalizer |
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Overhead switch/ Sectionalizer Larger image >Rosenberg Texas Larger image Sectionalizers are used to shut off power to a local distribution line, for line repairs or manage load shedding, or fire control where systems are not automated. Note sectionalizers are manually operated with a lever located at bottom of pole. The grid is designed to hold voltage stable. If several power plants shut down or demand exceeds supply etc, then voltage can drop below nominal. If voltage drops, then local power plant might shut down automatically. To avoid shut-down, the grid operator must load shed some customers to help grid stay operational while supplying power to key facilities such as sewage treatment and hospitals. Typically, the bulk power system, including transmission and subtransmission is mapped out, but in 2022, the local grid might not be mapped out at the customer or distribution level, making it difficult to engage in rolling blackouts if power company doesn't know which circuits go to which areas. Some areas receive power from a single line while others receive power from two or more lines etc. A circuit might be accidently switched on to a large area that would cause sudden voltage drop and risk grid failure. Mapping local distribution circuits can cost millions, and afterwards, constant updating is necessary, especially in areas experiencing growth etc. |
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| Capacitor bank | |
 Pole-mounted capacitor bankLarger image Larger image "Capacitor banks are used to improve power factor (PF), improve voltage, and reduce line losses on distribution lines. Capacitor banks shall have voltage and current sensing capability. Capacitor banks shall be connected grounded wye system. Are not installed on a Delta line." Note that 3 phase transmission, subtransmission and distribution lines are wired for WYE, where the line voltage (Hot to Hot) is higher than the phase voltage (Hot to Neutral) by a factor of the square root of 3, while line current and phase current are the same. Source; 3-phase power math .pdf Resources: What-is-power-factor.pdf Pole-mounted-three-phase-capacitor-bank pole-mounted-three-phase-capacitor-bank55.pdf Difference Delta and WYE |
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 Capacitor
bank on 3-phase distribution lineLarger image This capacitor bank includes an overhead switch or sectionalizer, located on right side of pole, that can be used to by-pass the capacitor. This 3-phase distribution line supplies power to multiple neighborhoods, including my neighborhood HVAC motors at each home are inductive loads, that cause reduced power factor on the line. Transformers without load also create reduced power factor. Inductive loads such as motors, contactor coils, relays.... consume large amounts of amperage before voltage during start up ... causing voltage to lag behind amperage. Resistive loads such as lights and heaters... consume voltage and amperage at same time, without lag. |
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 Effective
operation of
down-line distribution capacitors optimizes the feeder voltage profile
and minimizes VAR flow.Voltage Regulators and Controls "Capacitors and regulators are used to flatten the feeder voltage profile. The capacitor acts as both a voltage and power factor device to deliver the optimal feeder voltage profile." "Power factor correction is a crucial element in improving energy efficiency and reducing losses. Capacitors are used to correct the distribution feeder VAR flow." "VAR control is only required when both current and voltage are out of phase within an electrical circuit." Open Rack Layouts Distribution control system Capacitors-on-Rural-Electric-Systems.pdf , Power Factor equals kW divided by kVA Hubble capacitors |
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 Larger image"Voltage regulators are devices that maintain distribution voltage within a specified range of values. They are used by power companies to minimize voltage drop and to ensure that the proper voltage is supplied to customers." Voltage regulator can level average voltage across the 3 Hot wires, often resulting in energy savings. "A line voltage regulator automatically adjusts the voltage to a regular level, makes the distribution grids “smarter”, and allows the infeed of higher amounts of renewable power." "New distributed energy resources, such as solar, combined with the growth of sophisticated loads creates voltage challenges on distribution network systems. Existing voltage control devices cannot maintain a consistent voltage profile, especially when trying to manage the intermittency of these new resources and loads. These new loads and intermittent resources tend to drive the voltage regulation beyond its designed capability, and reduce the typical voltage regulator life expectancy and increase the ongoing maintenance cost for reliable operation." "Voltage regulators are cost effective solutions to regulate voltage without compromising quality and reliability...". Voltage-Regulators.pdf |
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More overhead wiring Resources: Sectionalizer Hoist stick pdf Jumpers etc pdf Jumper clamps pdf Line construction tools Web ratchet puller pdf Pulling-electric-wire What-is-3-phase-electric Web strap ratchet lever hoists lineman’s puller hot stick hoist options Tension Puller pullers and tensioners Compression clamps Jumper clamps Power line tools/ pdf Arc protective clothing pdf |
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Compression
Splices After wires are pulled together by tensioner, a compression splice or sleeve is added to securely connect both sections of wire. The conductor is cleaned and inhibitor applied to both surfaces, and then spliced is applied. "There shall not be more than 1 splice per conductor in any span, and preferably not in adjacent spans." Resource: Hubbell-splices-and-sleeves.pdf Splice repair Splices-en.pdf Inhibitor .pdf |
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Lineman's utility cart carries rolls of smaller wire
used for neutral,
grounding and guy wires, and triplex drop wire for residential service. Each lineman is trained for specific voltage range because protective equipment, parts, materials, safety-equipment and other factors vary by voltage. Conductor sizes range from 12 mm² (#6 American wire gauge) to 750 mm² (1,590,000 circular mils area), with varying resistance and current-carrying capacity. Thicker wires would lead to a relatively small increase in capacity due to the skin effect, that causes most of the current to flow close to the surface of the wire. |
Rosenberg Tx Larger image Another image Another image Rosenberg Texas  Larger image Another image |
Fig-A shows freshly cut 37
strand 'concentric round' aluminum bare overhead Distribution conductor
with strands of wire splayed apart. Fig-A is called 'concentric round' since each strand is identical, each is round, and cable is round. Diameter 0.795." or .455 square inches. This wire was lying on the ground as part of the installation of new Distribution lines along the freeway. Note: "each layer in a conductor is wound in the opposite direction" Fig-B shows 28 strand bare overhead Transmission conductor with 7 strands of high strength steel surrounded by 21 strands of trapezoidal-shaped aluminum wire. ''Air space between strands can be reduced by compacting the aluminum conductor into trapezoidal shape for a more compact wire size." Wire in Fig-B was lying on the ground as part of the installation of new Tansmission lines along a local highway and estimated at 1-1/4" diameter. "Overhead wire can have 70-127 strands and be 2.3" or more in diameter, and made from a variety of aluminum alloys. 12mm² to 750 mm²." Household wire can be 7-19 strands and less than 1/4" across Wire sizes are given in kcmil. Example wire is 954 Circular Mils (kcmil) = 483.4 square mm ... since 1000 square mm = 1.55" ... 500 square mm = .75 square inches. 954 kcmil = .7493 square inches of area = diameter .97" Zinc coated and aluminum coated steel wire are used where temperatures exceed 200° F. |
| Resource
pdf: Ampacities-of-overhead-conductor Amp-rating-power-lines.pdf Overhead-Installation-Guide 4_overhead_conductors Mechanical-Design-of-Overhead-Lines |
Advanced-Conductors-for-Overhead-Transmission Design-overhead-distribution Overhead Conductor Installation .pdf Overhead-aluminum-conductor Wire & Cable Technical Handbook.pdf |
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Size comparison steel core
28-strand Subtransmission wire with
compressed trapezoidal shape vs 37-strand concentric round aluminum Distribution wire. Trapezoid design eliminates much of the air space between strands, allowing higher-voltage wires to have more compact diameter. Each layer in a conductor is wound the opposite direction  |
  Ordinary ACSR conductors can be operated at 185° - 200°F (85°C-95°C) HTLS (high temperature low sag) conductors are made from aluminum alloy and core materials that can be operated continuously at 300°F-480°F (150°C-250°C) Higher temperature cost more but mean power lines deliver more power without increasing size (and weight) of conductors that requiring major upgrade to stronger conectors, poles etc |
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 need, 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 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 main issue. Galvanized wire is used. Galvanized steel is a poor choice of conductor for areas with high load Overhead conductors can last at least 40 years Resources: Overhead conductors pdf Amp rating of power lines Ampacities-of-overhead-conductor.pdf Utility-Wire-and-Cable.pdf Overhead-wire-types.pdf Wire types pdf Overhead aluminum conductors General cable/ overhead conductors ]General cable/ overhead line solutions |
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Battery-powered, hydraulic
cutting tool Each tool has different rating. The one in photo is rated to cut 1/2" steel re-bar up to 1.5" aluminum conductor, etc. Various types of battery-powered tools are important for line work, for crimping, cutting wire, tightening bolts to correct torque etc. Resource: Huskie-lineman-tool-Catalog |
 Resource: Spun-Concrete-Poles-Valmont-Utility.pdf For subtransmission and distribution |
 Note the ground wire traveling down full length of pole RCC reinforced concrete pole/ High-voltage Subtransmission tower/ with local distribution lines located bottom right corner of photo. Vertical bundling for twin conductor suspension, Vertical Bundle Assembly Suspension Clamps/ located in Rosenberg Texas Resource: UEP_Bulletin_1724E-2044.pdf |
 Distribution line Larger image Rosenberg Texas |
3-phase distribution
lines 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. Resources: Spun concrete poles Spun-Concrete-Poles-Valmont-Utility.pdf prestressed-concrete-poles.pdf Dead end clamps pdf |
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Compression
hot clamp Color difference
added for clarity
Distribution
hot line connected to another
distribution hot line.Used for higher amperage application compared with hot clamp used for home. Wires shown are 3/4" diameter, 37 strand aluminum Resource: Overhead-primary-clamps.pdf |
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Hot
clamps For connecting wire to distribution line Resource: Hot clamps pdf |
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Distribution 12,0000 V Suspension clamp and silicone strain or dead end insulator Suspension clamp has 4 bolts that are tightened against wire. The clamp holds wire and keeps it from slipping. Used when suspending wire across long distance or at pole located at corner Strain insulator vrs suspension insulator vs dead end insulator: Horizontal vs vertical vs horizontal end of line, they are the same except used different ways. Resources: Mechanical design overhead lines Transmission power pole parts.pdf Overhead-primary-clamps.pdf Dead end clamps pdf Suspension jumper support |
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Composite
insulators are two metal ends connected by a
'fiberglass' rod that is both flexible and non-conductive. The fiberglass rod is covered with silicone sheathing that includes a number of semi-rigid fins called sheds. |
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Distribution 12,0000 V Strain clamp and silicone strain insulator Power company installed new poles for freeway construction. When new poles were wired and energized, the old poles were taken down. Hardware was removed from old poles. This assembly was left along freeway overnight .... I picked it up from the ditch, photographed it, then returned it to the ditch 2 days later. It was about 36" long. Surprising was that the fins on the insulator were rubber (silicone) material, as was the coating around the insulator. The fins are for dissipating heat and preventing flashover. Resources: Composite-insulators.pdf |
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Subtransmission
installation Quadrant Strain Clamp Quadrant style deadends or strain clamp Let the wire make 45% bend  Resource: Hubbell-strain-clamp.pdf Anderson-dead-end-clamps.pdf |
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220,000-240,000 volt Transmission
assembly Resource: Hubbell-Power-Systems-Deadend.pdf |
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230,000-324,000 volt Transmission
assembly (Insulator shortened for illustration) |
 Distribution
12,0000 VLarger image Another image Strain clamp and porcelain strain insulator This older installation used porcelain strain insulators and wood pole. The function was to bring 3 Hot wires and a neutral across the freeway and connect onto the 3-phase distribution line that runs parallel to freeway. The pole and wiring were updated when new freeway construction required poles pushed back farther away from road. The wood pole was replaced with a 26,000 lb spun concrete pole, all new wire and hardware installed and the porcelain strain insulators were replaced with new style silicon insulators. Pin type porcelain insulators were still used with the new installation. |
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Strain clamps Resource: Hubbell-Tee-and-jumper.pdf Hubbell-dead-end-strain clamps.pdf Anderson-dead-end-clamps.pdf |
 Compression Tees are used
when there is no pulling stress on the conductorStrain clamps, shown above, are designed to hold the conductor by force, using bolts and clamps, while the conductor passes through to another connection point. Compression Tees, splices, and line repairs are different. They must hold wires together while preserving conductivity between two different surfaces. The challenge with compression is that "two conductor surfaces (e.g. connector and cable) can never be perfectly matched." Read more |
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 Larger image Rosenberg Texas |
3-phase
distribution
lines 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 Compression connection is accomplished with hand tool that looks similar to bolt cutter Resource: Grounding steel poles Crimping tools |
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Aluminum distribution
clamp Before installation, both conductors are cleaned with wire brush and coated with inhibitor Resource: Crimping tool pdf Cutters pdf |
| Distribution pole | |
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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 that is assembled to specification. For example the polymer riser (insulator) must be set at specific distance from bottom of pole, and from each other etc. Wood poles are used for spans up to 50 meters. Wood poles rot underground after 20-25 years Cannot be used for voltages higher than 20 Kv Resource: Mechanical design of overhead power |
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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 |
Distribution pole pre-assembled on ground Larger image |
Line post insulator
attached to distribution pole with offset mounting bracket Also shows 5/8" galvanized bolts with curved washers ... and my new size 12 shoes. |
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Distribution
line and hardware removed from old pole Includes 2 ceramic line post insulators, 5/8" threaded bolts, 1 composite insulator on left, cut piece of 7/8" conductor and partial view of strain clamp far left. When replacing old distribution line, the old lines are sectionalized (conductor is cut but still suspended in the air with a sectionalizer. see image), new poles, conductor, and hardware are installed alongside or nearby, new lines are energized, the hardware and wire from old pole are removed, and old pole is cut off just above the communication cable(s) that are strung along same route. The communication company then removes their line, moving it to new poles. Old pole is cut off or pulled from ground and taken away. |
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Top of power pole A shackle insulator has been added to pole. This type of insulator supports a drop line to another pole ... that typically travels to another pole with transformers ... that supply power to a commercial or residential location. |
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Standoff is for holding the neutral wire that will drop down to the
transformer, or to the ground wire, and ground rod. Extra length of neutral wire looped back in toward the pole will be attached to Neutral wire at top of pole. Shackle or spool insulators can be made of ceramic, glass, polymers etc and are used to hold the triplex drop line going to a home. The fiberglass guy strain insulator is attached to pole at one end and guy wire at other end. The purpose is to insulate the guy wire from any possible contact with live voltage from the pole. Resource: Guy strain insulator .pdf |
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Standoff for neutral wire Each wooden pole on the distribution grid has a Neutral-ground wire that travels down the side of pole. Standoffs are used to keep the neutral 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 neutral is below the height of the hot wires, the ground wire is attached directly to pole. The neutral also connects to Neutral going to business or home At the transformer, a ground wire is connected to neutral and to each transformer Bottom of pole, the ground wire enters the soil at a depth specified by local code to meet proper ground for the type of soil conditions Resources: 3-phase electric Household electric service Why you need ground Formulas-for-Ohms-law |
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Standoff for Neutral wire with Neutral wire attached Extra wire will be connected to Neutral wire at top of pole |
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Neutral compression connection found where neutral
wires are connected together at top of pole, or connected to ground
wire. Hand crimped connection using crimp tool, Every pole has a Neutral-ground wire. The ground wire going into the soil at base of each pole always connects to Neutral The Neutral wire runs down side of pole to the soil when a ground connection is made Each ground is connection is determined by type-of-power plus location, type of soil etc Neutral wire runs from pole to pole across the entire grid. Ground wire is connected to each neutral across the grid to stabilize and protect grid from overvoltages, surge etc. Before installation, both conductors are cleaned with wire brush and coated with inhibitor |
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Copper ground wire 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 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 permafrost. Grounding specifications vary by soil, type of pole, voltage, etc. Resource: Why you need ground Overhead grounding standards pdf |
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Ground wire, ground rod, butt coil, guy wires etc are
pre-installed on pole before pole is set in hole. "Connections in a ground network are subject to severe corrosion, high mechanical stress due to electromagnetic forces, and rapid thermal heating due to high current magnitudes during fault conditions." In addition to the physical strain, ground connections must also withstand high thermal shock due to the passing of fault current. Depending on how the ground system electrodes were sized and the duration of the fault, conductor temperatures may reach 250°C (maximum for copper in tension applications) to well in excess of 600°C (copper melts at 1085°C). The connector must be capable of handling these extreme temperatures without loss of integrity." Source |
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Neutral wire runs full length of pole to the point
where the ground wire connects. Here is the connection point between the copper ground wire and the aluminum-coated steel wire that runs to top of pole On some poles, 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 #4. Copper can never be installed above the aluminum to prevent copper salts from washing down on aluminum. |
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The Neutral wire on each pole or tower, no matter if
pole is wood, steel or concrete, or used for transmission,
subtransmission or distribution, is bonded (connected) to a ground
(earthing) located at bottom of pole. The massive array of grounding protects the grid from overvoltages, lightning strikes etc and carries throughout the grid, all connected together by the Neutral wire continuously from power plant to end user. |
| Guy Wires | |
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Guy strain insulator connects to pole. Guy wires cannot be energized with electricity. To solve problem, guy strain insulators are attached to pole at one end and then attached to guy wire lower down. The guy wire is then attached to anchor that is driven into ground. Resources Performed-Guy-Strain-catalog.pdf Preformed_Guy_Strain_Insulator.pdf |
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Guy
wire anchor The load resistance of an anchor is based on soil conditions. Resource: Hubbell anchors |
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Assembly of parts before installing guy wire for new
pole Resource: Guy markers |
 Larger imageTripleye® Guy Adapter with a Pulling Eye is made for attaching 3 guy wires to a single anchor. Other guy adapters are made for 1 or 2 guy wires. Load capacities vary by type of soil and are determined by installation torque. Each guy wire has a Guy Grip that wraps around the guy wire and attaches it to the guy anchor. Guy wires do not carry voltage and are safe as long as attached to the guy anchor. In Houston, a boy was electrocuted when a loose guy wire was being used as a 'grapevine' for swinging back and forth. Guy wire came into contact with live power up at the transformer. Guy markers are important for safety. Without the yellow guy marker, it would be easy to walk into a guy wire and trip or injure oneself easily. Resource: Hubbell anchors Hubbell anchor tools Guy grips |
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Steel guy wire is stronger and less expensive than alternative metals |
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Guy
wire ''Down guy travels downward at angle and is attached to guy wire made of 7-strand galvanized wire. Diameter of wire and number of guys vary by load requirement. The guy wire is attached to the anchor. Parts include the lead section, and extensions. The anchor lead section and extension are screwed into the soil to the correct depth based on soil and load. A soil probe is used test the soil, and results compared with charts that give correct soil classification. Extensions are used to increase depth. The guy wire connects to an extension which is connected to the anchor. The entire guy assembly is connected together and to the pole using hardware such as anchor rods, thimble eye, couplings, eyebolt, eyenuts, shakel, clevis, wrap guy, guy lock, guy grip. The down guy is covered with a shield at the bottom, called a guy marker. The purpose is to make guy wires visible to the eye and avoid collisions and encounters with people, animals etc that might get hurt or damage the guy.'' Resources: Guy markers Guy anchors Aluminum conduit standoff Deadend-guy-en.pdf |
| Connect electric wire to insulator | |
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Formed Wire:
Deadends for Guy Wires, laying on ground next to 7/8" diameter distribution conductor (wire). In lineman slang, wire ties are called wiggle wires. Wire ties are used to attach the conductor to the insulator at each pole, and attach guy wire to anchor etc. Wire ties are prefabricated for each wire size When viewing electric repair trucks and supply trailers on the road, you can see the pre-fabricated ties hanging on back of vehicle Resource pdfs Lineman slang Hubble Brenco Formed-wire |
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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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Preformed Tension Clamp Preformed Wraplock Tie 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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Simulation of connection using photoshop. The tie wire is wrapped 1 turn around cap Rubber insulator on side tie forms a barrier between wire and cap Tie is twisted around the wire.  |
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Connection at top of pin insulator Resource: Preformed Wraplock tie Types-of-insulators.pdf |
| Pulling new subtransmission wire | |
 Larger imagePulling new subtransmission wire requires specific size sheaves depending on size of wire etc. The power company set this metal crate at base of each pole. Each sheave has 3 separate wheels so power company can run 1,2 or 3 wires. See image Next they raised each sheave, one at time, up to the correct height where two men in a bucket truck attached the sheaves to the 3 line post insulators. |
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Suspension insulators and sheave Double String Dead End Polymer Assembly |
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Line post insulator is
made from hydrophobic silicone polymer, or silicone rubber compound. Bottom Fitting is an aluminum Gain Base. The live end fitting on this one is called a Tear Drop Blade. Other types include Horizontal Clamptop. Source Hubbell The power line was designed for two conductors (wires). Each wire was pulled separately. Resource: Line-post-Insulators.pdf |
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There are 3 large spools of wire at one end of the pull
that are
held in a machine called a tensioner, and at other end is a machine
called a puller. First they run 3 steel cables from the puller that is strung through each sheave and goes to the tensioner. The 3 pull cables are attached to the 3 conductors at the tensioner. See image The puller pulls the wire through the sheaves to the end point, while the tensioner reels out the cable, ensuring the wire is not pulled so hard that it splays apart the strands. The wire must maintain it's structural shape and design to function correctly. Damaged wire can overheat, causing inefficiency and point of failure. |
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