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What is 3-phase electric/ Power transmission from generator to end user

power generation

Power Generation Book

Co-generation is growing market as demand for reliable energy grows.
Book by Singh covers the basics, and the engineering math. Future business and industry leaders should be aware of the complexity and variability of electricity.

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3-phase electric Power company generates 3 phase electricity
and transmits electricity across high voltage lines....
Steam turbine, gas engine, wind or water rotates magnet past coils of wire, generating AC or alternating-current electricity.
Solar panel arrays produce DC or direct-current electricity that must be converted into AC before being transmitted on the same electric lines used by AC.
Co-generation can be added at any point along the line, including end user generator, solar panel array or windmill.
generatorSteam turbine or gas engine rotates magnet past coils of wire. This is AC alternating current generator
Although it's unknown exactly what electricity is, it can be described as movement of electrons.
Passing a magnet over a coil of wire causes lightweight negatively-charged electrons to come loose from orbit around heavier positively-charged protons and begin jumping from atom to atom in a cascade of electrons moving down the wire. This is called electromagnetic induction.
The 3-phase power plant generator uses this principle by rotating a large electromagnet past 3 separate stationary coils located exactly 120 degrees apart, shown in Fig-1 as A B C.
The three coils of wire each have 2 ends. One end of each coil is joined together to form the Neutral wire, while the other three ends are connected to three separate Hot lines. The three hot lines and neutral exit the power plant along high voltage transmission towers. See image

In the US and Americas, the generator rotates 60 times per second (called 60 hertz or 60 cycles or frequency). In Europe, Asia, Africa etc, the grid is 50 cycles. Appliances and timers made for 60Hz will not function with 50 Hz etc, while some devices are rated 50-60Hz and will work worldwide.

Each time the magnet rotates past a coil, it produces a pulse or force of voltage that pushes electrons (amperage) down the wire. The generator output is measured in megawatts (million watts). Volts x amps = watts, and watts is Power.

As the South pole of the magnet approaches a coil, the electrons begin moving one direction on the coil of wire.
As the South pole moves away and the North pole approaches the coil, the electrons slow and come to a stop, then reverse direction as the North pole passes.
The pulses of electricity reverse direction each time the N and S poles of magnet pass, in an endless cycle of reversing electrons, creating what is called alternating current. Current is amperage, and means current of electrons.
Because the magnet passes each coil at different times in the rotation, the pulse of electricity on each coil is out-of-phase with the other coils. The result is a three phase wave of electricity that is transmitted from the generator across 3 separate wires. The entire grid is energized with current that oscillates at 60 cycles per second, with electrons racing back and forth on the wires, accelerating one direction and then back again 60 times per second, and each wire carries electrons that are accelerating at a different rate from the other wires. Therefore each wire is 'out of phase' with the other wires, creating a potential to connect electric loads between any two or three of the hot wires. Likewise, each of the three hot wires is out of phase with the neutal wire, meaning that hot to neutral also has potential to connect loads.

More detail
Household generators, sold at local store also produce AC electricity, but not 3-phase ... instead they produce single-phase alternating current by rotating one coil of wire, located in center of generator, past two large magnets located on outer edge of generator.
Difference single phase and 3 phase

Power plant generators (Fig-1) have three coils that are located on the outer edge, and a large electromagnet is located in center. Electromagnet can produce significantly more force than magnetized metal. The result is a generator that produces 30,000 volts with massive output that supplies power to hundreds of thousands of homes and businesses over vast distances, while small household generator might have trouble supporting the loads in a single home.
Paradoxically, it requires so much electricity to run a power plant, that it can consume up to 25% of total output just to run the power plant and electromagnet. To avoid risk of prolonged blackouts, each power plant is connected to other power plants so if one or more plants shuts down, they can be re-started using electricity from other plants. Power plants typically have 3 phase back-up generators that burn gasoline, or natural gas.

So how did they get enough electricity to start the first power plant generator?
Answer: Using smaller and smaller generators until a small generator with a coil on the inside and magnets on outer edge started it all. The ordinary magnet and coil of wire are the root of AC electricity.
Read about generators
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Generator and turbine Generator and turbine
Fig-2 shows turbine and generator used in coal-fired power plant.

Coal or gas or nuclear rods boil water into steam.
High pressure steam explosion accelerates the turbine.
Turbine rotates electromagnet located inside generator.
3-phase output is transmitted to the switchyard transformers that raise voltage for transmission.

Backup diesel generators, Gas engines, waterfalls and windmills can also produce electricity without steam, using water to cool parts.
Resource
See illustration of coal-fired plant
Web link
generatorLarger image
WYE generator/ line and phase voltages
Fig-3 shows internal wiring of a power plant generator, with electromagnet in the center ... and 3 coils, 1 2 3 on outer edge of generator.
One end of each coil is connected to a Hot wire or Line wire ... Line 1, Line 2, Line 3. These wires become the 3-phase output along transmission lines.
The other ends of each coil are connected together to form the Neutral wire.
Power is transmitted to end user over 3 Hot wires or Line wires that are accompanied by the Neutral wire.

Line voltage means there is power potential between all 3 hot wires, and potential between any two of the three Hot wires.

Phase voltage means there is power potential between any Hot wire and the Neutral.

More detail
To control and protect the grid, the Hot wires are connected to circuit breakers at each substation. Circuit breakers limit the number of amps (electrons) that can flow down the wire at any given moment.
Voltages on the power lines remain steady (except for brief surges etc), but the flow of amperage rises and falls with usage. With more amps flowing when more loads are operating. The wire always offers resistance to the flow of electrons. Resistance is like friction and causes heat on the wire. If the demand for amperage exceeds capacity of wire, the wire will get hot and substation breaker will trip, causing brownout, blackout and other reliability issues. Ampacities of power lines

The Neutral forms a continuous, unbroken connection across the entire grid. The Neutral is never switched off. Only the Line wires or Hot wires are switched or connected to breakers.
The Neutral is bonded to the ground wire at every point along the way ... making a connection to earth at the power plant, at each transmission tower, each subtransmission pole, each substation, and distribution pole ... including every home and business .... forming a massive array of grounding.
The Neutral is bonded to the array of grounding to protect the grid from anomalies and overvoltages ... basically the Neutral-ground system ensures grid reliability, re-directing power surges, insulation failures, etc safely into earth.
Overall, the Hot Line wires are protected by fuses, breakers, surge protectors etc, while the Neutral is protected by the ground.
More detail
3 oscillating pulses of electricity leave generator
3 out-of-phase Hot or Line wires leave power plant generator.
Fig-4 shows 3 oscillating waves (sine waves) that represent the rise and fall of voltage over time on each of the 3 Hot wires. The rise and fall is caused by the generator rotating 60 times per second, or 60 cycles, also called frequency.
Note that each wave is 1/3 cycle behind the other. This is caused by the generator magnet hitting 3 different coils at different times during rotation. As the north pole of the magnet gets closer to the coil, the voltage climbs, until it reaches peak just as the magnet arrives, and then voltage declines as the magnet moves away.
Voltage drops to zero for a brief moment on the coil when both south and north are equidistant away from the coil, and then voltage begins to rise again as the south pole gets closer.

For the purpose of this description, electricity has two dynamics, volts and amps. Volts x Amps = Watts or Power. During the brief moment that voltage drops to zero, the electrons also stop moving. There is no voltage or amperage on the line, which means wattage or power output on that line is zero. This is represented by the black horizontal line in middle of sine waves.
However the generator is at zero volts for only an instant, which means the average voltage on any one of the three wires is always above zero. And because all 3 Hot wires are working together, the average voltage on a 3 phase circuit is never zero since no two wires are at zero at same time, as represented by the red horizontal lines in Fig-4.

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Why use 3-phase vs single phase?  The single-phase sine wave illustation shows that single phase delivers lower average voltage than 3-phase.  This means a 3-phase motor receives higher average voltage than a single phase motor ... resulting in higher power output per amp. Since wires and conductors of any type offer resistance to the flow of amperage (electrons) which causes heat loss (power wasted in heat), then a motor that runs on lower amps has lower heat loss per Hp of output, and therefore greater efficiency. Lower amps also means smaller wire size can be used, helping offset cost of running a third wire.
The same is also true for transmission and distribution. Three phase has less heat loss per megawatt delivered than single-phase.

Three-wire 3 phase electricity is more efficient than single-phase for large area uses and motor loads compared with two wire single phase.

Residential single-phase electricity draws power off the 3 phase distribution lines by taking 1 Hot and a Neutral, and then using a transformer to split it into 2 Hots and a Neutral. More detail
As a result, household single phase delivers lower average voltage (represented by red lines on the single-phase sine illustration) ... this is because both wires experience zero volts and zero power at same moment (represented by both sine waves crossing the zero volt black line at same time).
However, the generator rotates so fast that voltage is at zero for such a brief moment that the average voltage, amperage and power is always above zero (red lines), so the lights stay on. But the average voltage per rotation for single phase is always lower than 3 phase, meaning single phase has lower output per amp, higher heat loss per Hp of output, and less efficiency. However single phase is less complicated and costs less to install since it has only 2 wires, and does not require calculations to ensure equal amp draw (or balancing) between all 3 hot wires as required for a 3-phase installation.
Resource
Difference between 3-phase and single phase
3-phase circuits and basic math .pdf
More detail
Figure 12-7 is a 'phasor diagram' that shows wire connections, and volt-amp measurements inside a power plant generator ... with 3 squiggle lines that represent each coil or winding inside the generator ... a common point (black dot) that represents where all coils join to same Neutral ... and 3 separate points (open dots) that represent where 3 hot Line wires connect to each coil and leave power plant.

Note, the generator coils are wired in parallel (instead of end-to-end in series) ... this is a called a WYE configuration ... also called Star configuration.
Coils inside a bank of 3 transformers that supply 3-phase service to commercial buildings can be wired in series, called Delta (Open Delta, High leg Delta etc), but a power plant generator is always WYE. What is high leg delta
In a WYE configuration ...each Line carries same voltage and amperage as other lines/ each coil carries same voltage and amperage as other coils.

More detail
Testing volts and amps:
(1) Voltage potential exists between any 2 of the out of phase hot Lines ... this is called Line voltage.
Line voltage is measured across any two Line wires. The Yellow meter tests 10,000 volts potential across Lines 1-2. The same volt potential exists between Lines 2-3 ...or between Lines 1-3. So Line voltage is the same on each Hot wire in a WYE configuration generator.

(2) Voltage potential also exist between any hot Line wire and the Neutral  ... this is called Phase voltage. Phase voltage can also be measured across a coil. The orange meter tests 5773 volts across a coil, which is the same as testing Line to Neutral.
In a WYE configuration, the Phase voltage is the same 5773 volt potential across each of the 3 coils. 
Phase voltage can be calculated using formula: Line voltage ÷ √3 (1.732) = Phase voltage.

(3) Why is the Line voltage 10,000 when it comes off a coil that tests 5773 volts?
Because Line voltage is a potential between two separate Line wires that come off two coils, not 1 coil.
In the WYE configuration, the line voltage is higher than the phase voltage by a factor of the square root of 3 (1.732).

(4) Current is measured as a flow of amperage (flow of electrons) that is being pushed through a single line, or single coil.
Line current, or amperage flowing on a Line wire: The blue meter tests 250 amps flowing along Line 3. Each line carries the same 250 amps.
Phase current, or amperage flowing on a coil: The green meter tests the same 250 amps flowing through the coil. Each coil carries the same 250 amps.
In the WYE configuration, the Line current and Phase current are the same amperage as each other.

In a Delta configuration, found in some 3-phase commercial electric services, where the 3 coils are wired end-to-end in series (instead of parallel like WYE) ... then relationships between line and phase volts and amps is different than WYE. What is high leg delta
The mathematics needed to explain the grid is much more complex than the 2-dimensional example shown here, because power generation is dynamic ... it changes over time ... the rise and fall of voltage on 3 coils and lines each time the electromagnet rotates past a coil, the variable flow of amperage depending on end user demand, the use of 3 wires instead of two, the changes caused when one of the 3 hot Lines has voltage drops or spikes, relationships that require square root of 3 (which is irrational number), power surges, malfunctions, sometimes unpredictable behavior of electricity and equipment, ambient weather conditions including heat wind and moisture etc all contribute to the complicated nature of electric power.
WA Parrish coal-fired power plant
Larger image Smither's Lake
Water is key for generating electricity using coal, gas, hydroelectric and atomic fuels.
Water is also used to manufacture solar panels and windmills.
No water, no electricity. No water, no crops, no plants, no animals, no life.
WA Parrish coal-fired power plant
 Located outside Houston Texas. Coal is brought in by train from Wyoming. Water from Smither's lake in foreground is used to cool parts and run turbine, etc.
Some water is recycled, while some is lost during operations, or evaporation.

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Water is pumped from Brazos River to fill the lake. Pump is located several miles upriver in Rosenberg, and water runs downhill for 20 miles in a dirt channel ... ending up at Smither's Lake. The lake is man-made. A natural water channel that drained to the Brazos river was dammed off to make the lake. The lake supports active population of birds, alligators etc.
During drought years, water for power plant has priority ... and no water is diverted into irrigation channels for surrounding rice fields ... so fields sit fallow or are converted to dry-farm crops such as cotton.

The stacks bellow out smoke continuously that can be seen from miles away.
Recent developments (2019) caused closure of 2 coal-fired plants in Texas ... resulting in record electric prices paid by consumers in the privatized Texas electric system, while electric prices have fallen in other states.
General talk suggests eventual closure of WA Parrish in favor of more profitable ways to generate power by employing nobody while the Parrish plant supports large and skilled workforce with good wages.
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Coal trains arrive from Wyoming and dump coal.
Bulldozers move coal into piles that feed into conveyors.
When coal is burned, it heats water into steam.
Water turning into steam releases massive amount of energy in a steam explosion.
Steam explosion accelerates turbine.
Turbine rotates generator at 60 cycles per second.
Coal ash can be recycled into driveways etc, but might contain risk of mercury and other contaminants.
Electricity leaves power plant
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Transmission substation or switchyard is located at power plant



Power lines leaving power plant ... with coal-fired plant and switchyard in background
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Electricity leaves power plant
Generator can produce 30,000 volt, high-amperage AC electricity.
High amperage is a problem. The flow of electrons (amperage) meets resistance from the conductor. The more amperage getting pushed down the wire by voltage, the higher the resistance. Resistance is like friction that produces heat on the wire. Heat on anything electric means power loss and inefficiency.

It is not economical to transmit high-amperage electricity because wires must be larger, towers moved closer, larger insulators, heavier switchgear, larger substation breakers, and more heat loss... causing greater expense and shorter transmission distance.

The grid is a balance of cost and function, so efficiency is paramount.

To solve problem of high amperage ... electricity from generator is sent to the Transmission Substation or Switchyard located at power plant.
Switchyard uses 'Step-Up transformers' to raise the voltage which reduces the amperage.
Volts x amps = watts or Power is a basic formula: Since volts and amps are inversely proportional, the same amount of Power can be delivered by raising voltage, which reduces amperage.
This is the function of the step up transformer ... to decrease Amperage, while raising Voltage.

As a result, high voltage, low amperage electricity leaves power station on transmission towers, ranging from 69,000 volts upwards to 750,000 volts.
It works well since more voltage means more force pushing fewer electrons (amperage) against the matrix (atomic structure) of the conductor (wire), which keeps resistance and heat loss low, allowing longer transmission of power at lower cost.

Resource
Electric power distribution system operation 1990/ pdf
Amp rating power lines
Power lines leave power plant
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Other large image
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Wide corridor of land is needed for power lines leaving WA Parrish power plant en route to Houston and surrounding areas. To lower cost of maintaining right-of-ways, Power companies are re-purposing some transmission corridors into commercial and recreational areas ... while careful not to endanger electric grid.
Many power lines leave power plant
Large towers might carry 500 Kv or 500,000 volts
Shorter wooden towers might carry 115 Kv to 230 Kv.
Air is a good insulator. Air space between wires and earth (or ground), and air space between wires and other wires act as insulation to  prevent high voltage on the bare aluminum wire from arcing to other wires or to the ground.

More detail
This group of wires is headed to Houston/ Harris Co and Fort Bend Co.
Other towers leave power plant and go different directions.
Use Google Earth to view local power station, and trace wires to local substations. And then follow wires into each town and neighborhood, and to more substations to end users.

Electricity is a wave that travels roughly at the speed of light.
If AC electricity is not consumed at moment when available, it is wasted, unless the AC is converted to DC and stored in a battery.
Cell phone and laptop batteries store AC power.
Electric water heater is indirect way to store electric power. Water stays hot in tank for several hours after power is off.
Transmission tower
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Original image
Tower carries 3 hot wires run in pairs or group of 4 conductors
Groups of wires leave power plant switchyard attached to insulators that are supported by the transmission towers. The number of Hot wires on tower can always be divided evenly by 3 since tower is transmitting 3-phase electricity.

Example tower on left has 12 Hot wires plus 2 smaller Neutral wires located at very top. Each transmission tower and pole are grounded. The Neutral is always bonded to the ground wire, and with earth throughout the grid.

Image below shows transmission wires running in pairs. Both wires carry same phase hot and are separated by wire tie. There is no power potential between these two conductors, since both are the same phase and both come from same coil on generator.

Larger images
Transmission groundEach steel tower is grounded on all 4 legs at base of tower
A steel 4-legged tower will have ground at each leg.
Ground wire increases reliability of grid, absorbing excessive voltage surges during disturbances such as lightning, malfunctions, etc.
The system neutral wire(s) located at top of tower connects to ground wires that run to earthing connection at base of each pole or tower. In this case, the steel tower is also used as a grounded conductor.

More detail
Each type of soil offers different resistance to ground. Low resistance is required so the ground connection can conduct electrical short or lightning strike.
Depth and type of ground connection is determined by conductivity of local soils ... and standard electric practice.
Warm, moist, clay, salty soils offer less resistance to ground. Cold, dry rocky or sandy soils have higher resistance to ground and may require more ground rods in parallel, or an array of parallel ground rods. Some installations require a continuous ground cable that runs parallel to multiple towers that bonds all the grounds into an array that can handle overvoltage events etc.
Frozen soils are non-conductive and offer highest resistance to ground.
Formulas and testing measurements are used to determine the type of grounding necessary for each installation, region etc.

subtransmission towerLarger image
System neutral/ or static wire
System neutral, or static wire is present on each pole and tower throughout transmission, sub transmission and distribution on the grid.

The neutral is continuous from power plant to end user. The Neutral is never switched off.
The Neutral is bonded (connected) to the ground each step along the way ... at every pole, substation, installation, home and business. All the grounds together create a giant ground array across the entire grid that is required to keep the grid stabilized.

Neutral is also used for 3-phase transformer configurations that provide commercial electric services, and necessary for all installations of single-phase household power.

More detail
Transmission and Subtransmission towers and poles are raised far above the ground , and are more susceptible to lightning strike. As a result, the Neutral wire is always installed at top.
With lower voltage, local distribution poles can have Neutral at top or, run below the Hot wires, with Hot wires at very top. It varies depending on exposure to lighting. If poles are susceptible to lightning strike, then the neutral wire or static wire is installed at the top above the Hot wires, and acts like a shield against lightning strike.
In local distributions systems, where poles might not be as prone to lightning strike, and keeping power up high and away from traffic and people is needed for safety, then the Neutral is run below the Hot wire(s), and the Hot wire(s) sit at top of pole.

More detail
Lightning
Electricity can be described as the flow of electrons between unequally charged materials. Insulators like air will slow or stop the flow of electrons unless the charge becomes great enough to overcome the insulation.
Remember, the amperage or flow of current on electric wires is made up of electrons. Electrons have a negative charge that is always different than the ordinary ground we walk on. Therefore all man-made electricity wants to find route to ground to equalize the electric charge. The ground rod array, along with substation circuit breakers help prevent damage and injury when an insulation failure gives electrons a route to ground.

There are other types of electric potential. For example, the electrical charge carried in storm clouds can build up massive potential when friction between rising columns of clouds will strip electrons away from their positively-charged protons. The protons and electrons are isolated into pockets that cannot equalize because air acts as an insulator.
When the differential charge becomes great enough, it will overcome resistance and suddenly equalize in bolt of lightning. Lightning can be confined in the clouds, or strike the ground below ... often hitting the highest point like a tree, house on hilltop, or transmission tower.
The static wire or system neutral is directly grounded to the ground rod array, that will absorb the massive overvoltage from lightning thus reducing damage.
If the lightning carries more voltage than the ground array can absorb, there could be a flashover onto the hot Line wires. The sudden surge of power will causes substation breakers and relays to activate and shut down the line.
An OPTICAL GROUND WIRE is a static wire with fiber optic cables embedded in the core for use as a communications path. 
Power transmission lines
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Transmission towers located in Sugarland Texas
Located near W. A. Parrish generating station in Thompsons Texas


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Electricity arose from advancements in all sciences across many centuries.
Each advancement was supported by climate, food production, governments, education, writing, printing, and increasing population.
It took millions of hours to invent electricity.
Today, it takes millions of hours each year to produce, manage and maintain electric power.
Imagine the number of labor-hours needed to cut grass along transmission corridors.

Insulated standoff Insulators prevent electrifying tower
Each transmission wire must be insulated away from tower or pole
Transmission wires are bare aluminum, aluminum alloy ... some with steel wire core for added strength
Wires cannot come into contact with poles or trees, or electricity will short to ground, causing possible fire and tripped fuse, loud crack sound like lightning
Larger-longer insulators indicate higher voltage, as air space is efficiency used throughout the grid as an insulator.
Puller Pulling new overhead cable
New wire is added
Trucks and linesmen are needed to pull new wire from pole to pole
As electric consumption increases, more wire is added
Diameter of wire and material used for wire is based on voltage and cost vrs transmission loss
Resources:
Pulling electric wire/ photos
Identify power pole parts
pulling new wire
Pulling electric wire/ photos
Wires arrive at distribution substation
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Another image
Wires from power plant arrive at Distribution Substation
Transmission wires from WA Parrish power plant arrive at a distribution substation.

Substations generally re-distribute lower voltage power onto many smaller poles going several directions. And can send high-voltage power forward to other substations.
The smaller poles shown in picture are lower voltage distribution lines, while the tall spun concrete poles carry high voltage transmission lines.

More detail
Distribution substations can be located by following power lines using google earth to see complexity of transmission (from power plant to substation), subtransmission (substation to substation) , and distribution (local substation to end user homes and businesses.
Co-generation
Small co-generating plants require a substation ... and  can be located near transmission lines to boost power during peak demand.
Natural gas powered co-generation can be brought online quickly to meet demand.
Water for co-generation generally comes from water wells. Again: no water, no electricity.
"2014, Co-generation is the fastest growing segment of electric generation."
Some feel that co-generation will meet demand for future growth. Of course, the capitalist system requires growth to pay interest on the debt, and avoid recession and depression ... so don't expect total extinction of coal and gas from the equation.
Co-generation plants strategically placed can ensure essential industries receive power, while other less essential areas and people experience shortage, as per most of the world.
One solution proposed small thorium generators located strategically close to end users ... but unknown what the difficulties are ... possibly price.
Successful promotion of solar and wind have taken center stage in 2020 ... and might be considered generation instead of co-generation, but downside is obviously darkness or lack of wind.
Rooftop solar is still a boutique-priced option that cost 2-6 more per Kwh than large commercial installations that change the configuration of arrays to maximize solar harvest under varying solar conditions. All forms of 'alternative' energy require hydrocarbon fuel and water to manufacture, transport and install.
Distribution Substation
Larger image of substation
Distribution Substation
Example shows substation fed by wires from power plant.
Substation might receive 500,000 volts from generator.
The substation reduces voltage, raises amps and transmits power out on several lines.
Local power lines sit moderately close to the ground compared with transmission towers. Because the air space between ground and hot wire is much closer, the voltage must also be lower to prevent high risk of arcing to ground.

To support need for economic growth and more consumption each year to feed the capitalist system, pay the debt and avoid recession, new generation capacity and substations must be continually added.
The disincentives for meeting the challenges facing our world are too apparent.
electric substation
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3-phase connects to Distribution Substation
Electricity from power plant to distribution substation
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Electricity from power plant to distribution substation
Illustration shows general concept 1) power-plant, 2) power plant substation with step-up transformers, 3) 500 Kv 3-phase power traveling along transmission towers, 4) 3-phase power arriving at distribution substation with step-down transformers, 5) 69Kv 3-phase power leaving substation on wood poles going to local businesses and homes.
Voltages vary.

Groups of three Hot wires arrive at distribution substation
Substation is for illustrative purpose and does not show all connections or activity

High amperage is bad for transmission because of heat loss, but high amperage is needed by end user
Very high voltage is good for transmission, but lower voltage is good for end user
Transformers solve the amperage-voltage problem
There is inverse relationship between volts and amps
Basic electric formula is Volts x Amps = Watts. Volts and Amps are inversely proportional.
When voltage is reduced, amperage is increased. The reverse is also true.
Electric company can use step-down transformers that reduce voltage and raise amperage. High amperage is needed at each business and home.
Electric company can use step-up transformers that increase voltage and lower amperage. Lower amperage means less heat on the wire, and is good for long-distance transmission.
Step up and step down transformers can be used anywhere as needed
Resource
Electric power distribution system operation 1990/ pdf
Power lines leave substation
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Many poles leave substation, traveling to each business and neighborhood
Wires from substation branch off many directions on many wooden poles, sending power all directions
Power can travel many miles from substation to local towns, or substation can be located near town, or near neighborhoods etc

Power poles shown image on left travel to local neighborhoods and businesses.

Follow power lines using google earth to reveal complexity of distribution network
Usually poles leaving substation carry several groups of 3-wires
Poles are generally wood, but can be steel. Voltages vary by type of tower, pole, and height from ground
Example wood pole might carry 115 Kv or 115,000 volts, while steel tower might carry 230 Kv or 230,000 volts or more
Each pole has ground wire running down pole and into the ground
Power lines leave substation
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These power poles go to another substation
Other poles leave substation, traveling to other substations
The line of poles seen in photo on left, leave substation pictured above.
The line of poles travel 15 miles to another substation, and then on to another substation.
Secondary substations also feed local lines.

This power line also feeds another substation which has step-down transformers.
At this point, the transformers increase voltage and lower the amperage, and then the power is again transmitted on tall steel towers to yet another substation with step-down transformers for local power consumption.
ground wire            Ground wire
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ground rod
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Each pole has ground wire
Ground wire is normally smaller than wires that carry power.
Grounding increases reliability of service.
Ground prevents excessive voltage peaks, provides ground connection for system neutral, and discharge path for surge arrestors.
Ground protects people who work on and use electricity.
Proper grounding helps mitigate damage from lightning.
Without a ground wire, overvoltages and other disturbances damage equipment at substation and end user.
Substations generally have multiple grounds to overcome resistivity of soil.
Soils that are warm, tightly grained, wet, and have high levels of dissolved salt offer less resistance to ground.
Loose, coarse, freezing, dry soils with gravel and low salt content offer more resistance to ground.
High pressure means less ground resistance.
Different regions have different grounding specifications.
Resource
Why you need ground wire in home
3 phase power lines
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3 phase arrives at local business
3 wires arrive at business

3 Hot power lines 1-2-3 on pole
Lines travel down street from pole to pole.
Drop lines from each Hot wire sends power to transformers: a-b-c
3-phase power
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There are different transformer configurations used to make different voltages
Each installation follows same general pattern
3-phase power
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Transformer wiring
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Transformer wiring/ how to identify transformer wiring
Image shows Delta Primary and 4-wire WYE Secondary
Primary is Delta: How do we know? Each hot wire connects to two transformers.... so they are wired in series
Secondary is WYE. One wire connects to all three transformers, and to Neutral. One wire from each transformer is Hot... so they are wired in parallel
System neutral connects to Neutral and ground
There are many different transformer configurations

This is 'most common type of wiring' because Delta has lower amps/ meaning less heat, so insulation on primary coil is less expensive.

Transformers can be wired different ways depending on the incoming electric supply and end user need.
Two key factors for the grid are economic performance and reliability.
Reliability is necessary because electricity must run clean without big-voltage spikes and low-voltage brownouts. Otherwise motors and HVAC equipment will have shorter lifespan.

Resource
Transformer configurations
Transformer manuals
Identify more illustrations of transformer wirings
-Transformers are used throughout the grid to change the ratio of volts and amps. When volts are increased, the amps are reduced, or if volts are reduced, then amps are increased. 

Inside each transformer are coils of wire called the primary and secondary windings. Each coil is wrapped around a laminated iron core or more efficient amorphous metal core. The metal core is shared by both coils, but the coils of wire are 'insulated' from each other. They are electrically separated. There is no wire in common between the primary and secondary coils, only the metal core is shared. How transformers work pdf

-Transformers work on the principle of magnetic induction where applying electricity to one coil of wire creates a magnetic flux that energizes the other coil of wire with electricity.
Strength of a magnetic field depends on the amount of current (amps or number of electrons) and number of turns in the winding. When current is reduced, the magnetic field shrinks.'

Each time the voltage is raised or lowered, the amperage is affected. Basic formula: Volts x amps = watts shows that volts and amps are inversely proportional. When you raise volts, it lowers amps. A group of 500,000 volt transmission lines have low amps and low heat which is good for long-distance transmission. But the switchgear and wiring for 500,000 volts is too large, expensive and dangerous for household or business use.
Using transformers, the power company changes volt-amp ratio to accomplish different objectives. The result is an ordinary household receives low volt, high amp power. It works nicely because 120-240 voltage can be safely controlled by small switches, relays, cell phone chargers etc contained within steel and plastic enclosures, while the amperage (heat) is controlled by circuit breakers (also called overcurrent protection) and then distributed to outlets, switches, dryer etc using correctly sized wire to match amp rating of breaker.

-Having different numbers of turns of wire, or varying the turns ratio, on each coil will reduce or raise voltage. Different voltages can be achieved throughout the grid by varying the number of turns on the primary and secondary coils.
Why are transformers used?
"Three-phase transformer banks are used in three-phase AC power circuits for the same reasons as single-phase power transformers in single-phase ac circuits, i.e., to step-up or step-down the voltages in the circuit and to provide electrical isolation (separation) between the primary windings (coils) and the secondary windings."

Transmission and distribution lines from the power plant are high voltage, low amperage to reduce heat loss. Heat occurs when voltage pushes amperage (current of electrons) against the matrix, or atomic structure, of the conductor. Using high voltage and low amperage means more force is pushing fewer electrons against the conductor matrix, which means less resistance from the conductor and less heat.
Ampacities of power lines
By reducing heat loss, electricity can be transmitted longer distance without losing power.

To prevent electricity from jumping (arcing) to other wires, or to the transmission tower, or to the earth, high voltage conductors (wires) are suspended high above the ground and spaced far apart, utilizing air as an insulator. The higher the voltage, the more space is needed to keep the voltage under control.
High voltage also requires large and expensive switchgear, and is extremely dangerous, making it impractical and hazardous for residential and commercial use.
To solve the problem, transformers are used throughout the grid to step up or step down voltage. Since amps and volts are inversely proportional, when volts are stepped down by the transformer at local home or business, amps are stepped up. The lower voltage can be controlled at home and business using small switches contained inside metal or plastic enclosures while amps are controlled with properly sized circuit breaker and wire.
3 phase surge suppression
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Capacitor bank on 3-phase distribution line
This 3-phase line is 7200 volts and supplies power to multiple neighborhoods, including my neighborhood
These lines also supply power to several businesses that use motors
With several motors or inductive loads on the line, it will reduce 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.
Capacitor banks help solve problems caused by voltage lag.

This protects motors of all kinds from surge, including the motors at local businesses, and homeowner appliances and HVAC unit.

Neutral wire at top of pole not shown.

Resource
Read about surge suppression for residential and commercial
3 phase service
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Example 3 phase service
Drop wires connect to insulators, and then loop into weatherhead, and down conduit mast into meter box
Image on left shows Meter box, 3-phase Meter, and breaker box
The box might contain cut off breaker, and not be the final breaker box

Wires drop down conduit mast and enter meter box.
There are many different services, and voltages, and wiring can vary to meet code.
service
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Example 3 phase service
3 phase weatherhead
Example 3 phase weatherhead
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Example 3 phase service
Showing secondary service wires, service rack with 4 insulators, weatherhead, and service conduit
3-phase arrives at building
Difference between single-phase and 3-phase
What is 208 volt
What is 277 volt
3-phase meter 3-phase meter has 7 prongs
3 Phase meters have 7 prongs that stab into meter box
Unlike household meter that has 4 prongs
3-phase meter
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3-phase meter box

Delta and Wye transformer configurations are wired same.
Illustration on left shows typical 3-phase meter wiring.
In the case of high-leg delta, the wild leg or high-leg connects to top right or Line 3 in illustration.
High-leg delta is a specific transformer configuration ... each hot wire is called a leg.
With high leg delta, the wild leg connects to top right terminal so it's location is identified since this wire carries different voltage potentials than other legs.

Ground wire connects to same terminal where neutral connects
Ground wire cannot be used as neutral, since ground wire is usually smaller gauge than neutral wire.
Neutral wire is same gauge as hot wires so it can safely carry same voltage as each hot wire.
3-phase service panel 3-phase service panel/ Neutral and Ground not shown
3-phase Power passes through a 3-phase electric meter that registers electric usage for billing.
From the meter, power enters a panel box, and connects to 3-pole  main breaker
3-pole means there are 3 places for wires to connect. And each pole is electrically separated from other poles.

Main breaker feeds each hot wire to separate hot busbar.
So there are 3 Hot busbars, each electrically separated from the other, and each carries power from one Hot wire
3-pole circuit breakers snap down over all 3 busbars, drawing power from each busbar, and then 3 wires leave breaker and go to motor switch, or other use etc.

Resources
How to wire 3-phase electric
See wiring for 3-phase non-balanced water heater
Example shows timer controlling 3-phase load

Illustration shows typical use for 3-phase.
3-phase load receives 3 hot wires and a neutral.
All single-phase circuits require 2 wires, while 3-phase requires 3 wires. The manufacturer and engineer design electrical equipment to meet the requirement for each application.
Note, the timer is ordinary 240 volt single phase, which shows that single phase 2-wire applications can be achieved by drawing two hot wires from the 3-phase.
It is also possible to achieve 120 volt single phase by drawing 1 hot from 3-phase and using the neutral (applies to 208volt 3-phase or high-leg services or buck-boost transformer)

Resources
How to wire 3-phase timers
How to wire T100 series Intermatic timers
Buck boost transformers
How to wire 3-phase
power plant to house electricity
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Read about basic household electric
Converting 3-phase to single-phase household power
One Hot wire is taken from 3-phase power lines
The system neutral and 1 Hot wire are used to make single-phase power
Resources
Residential single-phase power
Basic household electric wiring
Troubleshoot household electric

Power plant to house
Illustration shows 500 KV 3-phase transmission system from power plant to distribution substation > then shows 69 Kv 3-phase sub-transmission system to secondary substation > then shows 7.2 Kv 3-phase distribution system that supplies local area > then shows single-phase distribution system drawn from 1 hot wire on 3-phase that goes to transformer at individual home.
Voltage and amperage are inversely proportional.
Volts x amps = watts.
When volts are reduced at at substation transformer, amps are increased.
High amps are needed at the end user, because amps are the heat that does the work.
However high amps cause heat loss during transmission.
That's why transformer substations are needed: because they control volts and amps.
Each time voltage is reduced, the amperage is increased... and higher amps mean transmission distance is reduced.
So the 500,000 volt lines are used to distribute power long distance.
69,000 volt lines are used for shorter distances.
7,200 volt for local distribution.
Below 4000 volts, the distribution is inefficient because of heat loss

Generally, in the US, each home has a transformer that converts 7200 volt Hot and Neutral into split phase 120-240 volt service.
The home receive low voltage, high amperage
Each home has a transformer that converts 7200 volts into 120-240 single or split phase electricity
Sometimes more than 1 home will share a transformer... result is dimmed lights, or voltage drop each time heavy equipment such as HVAC turns on.

Transformers

Transformers
Transformers can convert electricity many ways.

Transformer manuals
Transforming electricity is limited only by physics governing natural world.
For example using a transformer, high voltage and low amperage can be converted to lower voltage and higher amperage used inside each home. There is inverse relationship between volts and amps shown in following formula: Volts x amps = watts.
See electrical formulas

High voltage 3-phase from the power plant can be converted into many different 3-phase voltages depending on which transformer is used. Read about Delta and Wye
The reverse is also possible: Using a transformer, single phase residential power can be converted into certain types of 3-phase.

Since solar generated power is DC (direct current) instead of AC (alternating current) a transformer called an inverter will convert DC solar power into more useful AC power. Different inverter voltages are available by wiring the transformer differently.

Transformers are 95-98% efficient
Transformers have primary side and secondary side
Primary side receives full power from generator at all times.
Secondary side supplies power to homes and businesses that do not draw full power at all times
As a result the overall efficiency of the grid is about generating the power so use and generation balance.
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Power company boils water using hydrocarbon fuel, or nuclear rod.
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Bath uses 20 gallons water (12-15 gallons hot water).
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3-phase wiringLarger image

How to wire 3-phase outlets and surge protection

How to wire 3-phase electric
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