How do Electric Transmission Lines Work?

Summary

In this episode of Practical Engineering, Grady explores the intricacies of electrical transmission lines, highlighting the evolution from local power generation to a vast interconnected grid. He discusses the importance of efficiently moving electricity over long distances, the role of power lines, and the engineering challenges involved. Key topics include reducing power loss through higher voltages, the use of transformers, and the safety considerations of high-voltage lines. The video also touches on the impact of conductor selection, environmental factors, and the emerging trends in local power generation and energy marketplace dynamics.

Takeaways

• 🔌 Power plants used to serve only local areas, but now most electricity is distributed through interconnected grids.
• 🏭 As power plants grew larger and moved away from populated areas, the need for efficient long-distance electricity transport increased.
• 🧵 Power lines, or conductors, are essential for moving electricity from production sites to consumers, but they involve complex engineering.
• 💡 Electric utilities aim to minimize energy loss on the grid, as they are only compensated for power that reaches the customer's meter.
• 🏞️ Power plants are often located in rural areas due to cheaper land, cooling pond requirements, and fewer objections from local residents.
• ⚡ Even good conductors like aluminum and copper have resistance, leading to energy loss as heat, which is more significant over long distances.
• 🔗 Ohm's law and the formula for power loss (P = I^2R) are used to understand and reduce energy loss in transmission lines.
• 🔋 Transformers at power plants increase voltage, which reduces current and energy loss, making power transmission more efficient.
• 🏭 High voltage transmission lines require careful design to ensure safety, often using air gaps for insulation and tall pylons to prevent arcing.
• 🔌 Three-phase transmission is common, with each phase spaced apart to avoid arcing, and connected to towers through insulators.
• 🌐 The power grid model is evolving with local generation from solar panels and changes in the energy marketplace affecting how electricity is distributed.

Q & A

Why did power plants traditionally need to be located near populated areas?

Power plants traditionally needed to be located near populated areas because electricity didn't have far to travel between where it was created and where it was used, and power generating plants were only able to serve their local areas.

What is the significance of the grid in modern electricity distribution?

The grid is significant in modern electricity distribution because it allows for huge, interconnected areas of power producers and users, enabling the efficient movement of electricity over long distances to reach customers far from power plants.

Why is it important to minimize energy loss during the transmission of electricity?

Minimizing energy loss is important because electric utilities only earn revenue on the power that reaches the customer's meter, and they are not compensated for energy lost on the grid.

How do power lines help in the efficient transport of electricity over long distances?

Power lines help in the efficient transport of electricity by stringing wires, or conductors, over vast expanses, allowing bulk transport of electricity from where it's created to where it's used.

What is the relationship between resistance, current, and power loss in a conductor?

According to Ohm's law, the power loss in a conductor is equal to the product of current squared and resistance. Reducing the current can significantly cut down on power loss due to the i-squared term.

How do transformers at power plants contribute to efficient power transmission?

Transformers at power plants boost the voltage up to very high levels, which lowers the current in the lines, reducing wasted energy and ensuring more power reaches customers.

Why are high voltage transmission lines designed to be tall?

High voltage transmission lines are designed to be tall to maintain a safe distance between the conductors and the ground, preventing arcing and other dangers associated with high voltage.

What is the purpose of the insulators used in transmission lines?

The insulators in transmission lines are used to keep a safe distance between energized lines and grounded pylons, preventing arcing and ensuring the safe flow of electricity.

How can the number of insulator discs be used to estimate the voltage of a transmission line?

The number of insulator discs can be used to estimate the voltage of a transmission line by multiplying the number of discs by 15, which gives a rough estimate of the line's voltage.

What are the challenges engineers face in selecting the right conductors for transmission lines?

Engineers face challenges in selecting conductors for transmission lines due to the need to balance strength, resistance, and cost. Even a tiny change in conductor size or material can significantly impact the overall cost and performance of the line.

How are high voltage transmission lines adapted to handle environmental factors like wind and temperature?

High voltage transmission lines are adapted to handle environmental factors by using stockbridge dampers to absorb wind energy, and by designing the towers to minimize EMF at the edge of the right-of-way. Additionally, the lines can sag during peak demands, which is managed by ensuring a safe clearance from the ground and vegetation.

Outlines

00:00

🔌 Evolution and Complexity of Electrical Transmission Lines

This paragraph discusses the historical shift from local power generation to the modern electrical grid, which necessitates efficient long-distance power transmission. It highlights the challenges of moving electricity over vast distances and the importance of reducing energy loss. The engineering behind transmission lines is explored, including the use of transformers to increase voltage and decrease current, thereby minimizing power loss. The segment also touches on the dangers of high voltage and the need for safety measures in transmission line design.

05:01

⚡ Design Considerations for High Voltage Transmission Lines

The second paragraph delves into the practical aspects of transmission line design, such as the lack of insulation on conductors due to cost and the reliance on air gaps for insulation. It explains the three-phase transmission system and the use of tall towers and insulators to prevent arcing. The paragraph also covers the role of shield wires in protecting against lightning, the importance of conductor material and size in relation to cost and performance, and the challenges posed by environmental factors like temperature and wind. Additionally, it mentions the use of stockbridge dampers to mitigate wind-induced oscillations and the considerations for electromagnetic fields and audible noise in transmission line design. The paragraph concludes with a brief look at the changing landscape of power generation and distribution, with the rise of local solar power and its impact on the traditional power grid.

Keywords

💡Electrical transmission lines

Electrical transmission lines are the systems that carry high voltage electricity from power plants to substations, where it is transformed to lower voltages for distribution to consumers. In the video, these lines are described as 'electric superhighways' that enable the efficient movement of electricity over long distances, highlighting their importance in modern power grids.

💡Ohm's law

Ohm's law is a fundamental principle in electrical engineering that states the relationship between voltage (V), current (I), and resistance (R) in a conductor: V = I * R. In the context of the video, Ohm's law is used to explain how voltage drop occurs in a conductor due to resistance, which is a critical factor in designing transmission lines to minimize energy loss.

💡Power loss

Power loss refers to the reduction in electrical power as it travels through a conductor due to resistance. The video explains that power loss is proportional to the square of the current (I^2 * R), emphasizing the importance of reducing current to minimize losses in transmission lines, which is achieved by increasing voltage.

💡Transformers

Transformers are electrical devices that change the voltage of an alternating current. In the video, transformers are mentioned as essential components at power plants that increase the voltage of electricity before it is sent through transmission lines, thus reducing current and power loss.

💡Conductors

Conductors are materials that allow the flow of electric current. In the context of the video, conductors refer to the wires used in transmission lines, which are designed to carry electricity with minimal resistance and power loss. The choice of conductor material and size is crucial for efficient power transmission.

💡Voltage

Voltage, or electric potential difference, is the force that pushes electric charge through a conductor. The video discusses how increasing voltage in transmission lines allows for a reduction in current, which in turn reduces power loss during transmission.

💡Resistance

Resistance is the opposition to the flow of electric current in a conductor. The video explains that even good conductors like aluminum and copper have some resistance, which leads to power loss as heat. Reducing resistance in transmission lines is a key consideration in their design.

💡Insulators

Insulators are materials that do not conduct electricity and are used to support and separate conductors in transmission lines to prevent short circuits. The video mentions that insulators, often ceramic discs, are used to maintain a safe distance between energized lines and grounded pylons.

💡Transmission towers

Transmission towers, also known as pylons, are the structures that support the conductors and insulators in high voltage transmission lines. The video describes how these towers are designed to be tall enough to prevent accidental contact with the high voltage conductors, ensuring safety.

💡Three-phase transmission

Three-phase transmission is a method of alternating current electricity generation, transmission, and distribution. It involves three separate AC waveforms that are out of phase with each other. The video mentions that most transmission lines are designed to carry electricity in three phases to increase efficiency and reduce power loss.

💡Stockbridge dampers

Stockbridge dampers are devices used on transmission lines to reduce the oscillations caused by wind, which can lead to conductor fatigue and failure. The video briefly touches on how these dampers absorb wind energy, contributing to the overall reliability of the transmission system.

Highlights

Power generating plants used to serve only local areas, but now most electricity comes from the grid, which is a vast network of power producers and users.

The need for efficient long-distance electricity transmission has grown as power plants are often located far from populated areas.

The engineering behind electric transmission lines is more complex than simply connecting wires, involving considerations of resistance and power loss.

Electric utilities only earn revenue on the power that reaches the customer, making it crucial to minimize energy loss on the grid.

Power plants are often in rural areas due to cheaper land, cooling requirements, and public preference for not living near industrial facilities.

Power lines are the primary solution for transporting massive amounts of electricity from production sites to consumers.

Even good conductors like aluminum and copper have resistance, leading to energy loss as heat, which is significant over long distances.

Ohm's law is used to calculate power loss, which is proportional to the square of the current and the resistance.

To reduce power line losses, resistance can be decreased by increasing conductor size or using more conductive materials.

Reducing current by increasing voltage is a key strategy for efficient power transmission, as shown by the i-squared term in power loss calculations.

Transformers at power plants boost voltage to very high levels before electricity is sent over transmission lines to reduce current and energy waste.

High voltage transmission lines require careful design to ensure safety from arcing and other high-voltage hazards.

Most transmission lines use air gaps for insulation rather than insulating materials around the conductors due to cost-effectiveness.

Transmission towers are tall to maintain a safe distance between high-voltage conductors and the ground to prevent arcing.

Electricity is transmitted in three phases, which is why transmission lines typically have three conductors spaced apart to avoid arcing.

Insulators made from ceramic discs are used to connect conductors to towers, and their number can give an estimate of the transmission line's voltage.

Static or shield wires run along transmission lines to protect the main conductors from lightning strikes.

The selection of conductors for transmission lines involves balancing strength, resistance, and cost, with even small changes affecting the overall system.

Transmission lines can sag when hot, potentially causing problems with nearby trees, and wind can induce oscillations that may damage the lines.

Stockbridge dampers are used to absorb wind energy and prevent damage to the conductors from wind-induced oscillations.

High voltage transmission lines generate magnetic fields that can interfere with nearby magnetic devices, so tower height is set to minimize this effect.

The audible noise of transmission lines is a consideration to avoid disturbing residents, reflecting the multifaceted design challenges of electrical infrastructure.

The traditional model of centralized power generation is evolving with the increasing adoption of local solar power generation and changes in the energy marketplace.

Electrical transmission lines, while seemingly simple, embody a fascinating complexity that is crucial for understanding our electrical grid.

Transcripts

In the past, power generating plants were only able to serve their local areas.

Electricity didn’t have far to travel between where it was created and where it was used.

Since then, things have changed, and most of us get our electricity from the grid, huge

interconnected areas of power producers and users.

As power plants grew larger and further away from populated areas, the need for ways to

efficiently move electricity over long distances has become more and more important.

Stringing power lines across the landscape to connect cities to power plants may seem

as simple as connecting an extension cord to an outlet, but the engineering behind these

electric superhighways is more complicated and fascinating than you might think.

Hey I’m Grady and this is Practical Engineering.

On today’s episode we’re talking about electrical transmission lines.

This episode is sponsored by Hello Fresh.

More on that later.

Generating electricity is a major endeavor, often a complex industrial process that requires

huge capital investments and ongoing costs for operation, maintenance, and fuel.

Electric utilities only earn revenue on the power that makes it to your meter.

They aren’t compensated for energy lost on the grid.

So if we’re going to go to the trouble of producing electricity, we want to make sure

that as much of it as possible actually reaches the customers for whom it’s intended.

The problem is most power plants are usually located far away from populated areas for

a variety of reasons: land is cheaper in rural areas, many plants require large cooling ponds,

and most people don’t like to live near large industrial facilities.

That means that massive amounts of electricity need to be transported long distances from

where it’s created to where it’s used.

Power lines are the obvious solution to this problem, and sure enough, stringing wires

(normally called conductors by power professionals) over vast expanses of rural countryside is,

in general, how bulk transport of electricity is carried out.

But, if we want this transport to be efficient, there’s more to consider.

Even good conductors like aluminum and copper have some resistance to the flow of electric

current.

You even can see this at home.

We can measure a small drop in voltage when a hair dryer is plugged directly into an outlet

and turned on.

Trying this again at the end of a long extension cord, the drop in voltage is much more significant.

This difference in power represents energy lost as heat from the resistance of the extension

cord.

In fact, this lost power is pretty easy to calculate if you’re willing to do a little

bit of algebra (which I always am).

Electrical power is the product of the current (that’s the flow rate of electric charge)

and the voltage (that’s the difference in electric potential).

For a simple conductor, we can use Ohm’s law to show that the drop in voltage from

one end of a wire to the other is equal to the current times the resistance of the wire

measured in ohms.

Substituting this relationship in, we find that the power loss is equal to the product

of current squared and resistance.

So if we want to reduce the losses in a power line, we have two variables to play with.

We can reduce the resistance of the conductor by increasing its size or using a more conductive

material, but look what matters even more: the i-squared term.

Reducing the current by half will cut the lost power to one-fourth and so on.

Going back to Ohm’s law, we can see that the only way to reduce the current and still

get the same amount of power is to increase the voltage.

So, that’s just what we do.

Transformers at power plants boost the voltage up to 100,000 volts and sometimes much higher

before sending electricity on its way over transmission lines.

This lowers the current in the lines, reducing the wasted energy and making sure that as

much power as possible makes it to customers at the other end.

This simple demonstration illustrates the concept.

If I try to power a hair dryer using these thin wires, it is not going to work.

The current required to power the dryer is just too high.

It creates so much heat that the wires completely melt.

That heat represents wasted energy.

But, if I first boost the voltage up using this transformer and step it back down on

the other side of the thin conductors, they have no problem carrying the power required

to run the dryer.

We’ve essentially swapped high current for high voltage, making the conductors more efficient at carrying

power.

What we’ve also done is make things much more dangerous.

You can think of voltage as electricity’s desire to flow.

High voltages mean the power really wants to move and will even find a way to flow through

materials we normally consider non-conductive, like the air.

The engineers designing high voltage transmission lines have to make sure that these lines are

safe from arcing and other dangers that come with high voltage.

Most long distance power lines don’t use insulation around the conductors themselves.

Insulating in this way would have to be so thick that it wouldn’t be cost effective.

Instead, most of the insulation comes from air gaps, or simply spacing everything far

enough apart.

Transmission towers and pylons are really tall to prevent anyone or any vehicle on the

ground from inadvertently getting close enough to conductors to create an arc.

Bulk electricity is transmitted in three phases, which is why you’ll see most transmission

conductors in groups of three.

Each phase is spaced far enough from the other two to avoid arcing between the phases.

The conductors are connected to each tower through long insulators to keep enough distance

between energized lines and grounded pylons.

These insulators are normally made from ceramic discs so that if they get wet, electricity

leakage has to take a much longer path to ground.

These discs are somewhat standardized, so this is an easy way to get a rough guess of

a transmission line’s voltage.

Just multiply the number of discs by 15.

For example, this line near my house has 9 discs on each insulator, and I know it’s

138 kilovolt line.

You’ll also often see smaller conductors running along the top of transmission lines.

These static or shield wires aren’t carrying any current.

They’re there to protect the main conductors against lightning strikes.

High voltage isn’t the only design challenge associated with electric transmission lines.

Just selection of the conductors alone is a careful balancing act of strength, resistance,

and other factors.

Transmission lines are so long that even a tiny change in the conductor size or material

can have a major impact on the overall cost.

Conductors are rated by how much current they can pass for a given rise in temperature.

These lines can get very hot and sag during peak electricity demands, which can cause

problems if tree branches are too close.

Wind can also affect the conductors, causing oscillations that lead to damage or failure

of the material.

You’ll often see these small devices called stockbridge dampers to absorb some of the

wind energy.

High voltage transmission lines also generate magnetic fields that can induce currents in

parallel conductors like fences and interfere with magnetic devices, so the height of the

towers is sometimes set to minimize EMF at the edge of the right-of-way.

In certain cases, engineers even need to consider the audible noise of the transmission lines

to avoid disturbing nearby residents.

Even with all those considerations, the classic model of the power grid with centralized generation

away from populated areas is changing.

The cost of solar panels continues to drop making it easier and easier to produce some

or all of the electricity you use at your own house or business and even export excess

energy back into the grid.

This type of a local generation happens on the distribution side of the grid, often completely

skipping large transmission lines.

On the other side of that coin, the energy marketplace is changing as well, and grid

operators are buying and selling electricity across great distances.

Electrical transmission lines may seem simple - the equivalent of an extension cord stretched

across the sky.

But, I hope this video helped show the fascinating complexity that comes with even this seemingly

innocuous part of our electrical grid.

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