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Updated Transmission Lines for Renewables: Electric Powerways

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The electric energy grid is designed to transmit power from central generating stations, such as coal burning power plants, to areas of consumption, cities. As distributed renewable energy sources, for example rooftop solar, gain in popularity and add energy inputs to the grid from a variety of locations, this traditional design creates a challenge. Transmission lines must be updated so that they are able to transmit power from various energy sources, rather than a single generating station.

Another issue is that traditional transmission lines can only be operated at the capacity of the line that loads to full capacity first. While transmission lines may be rated to carry a large amount of electric energy, it is unlikely that most lines will ever carry their rated load. This creates a problem as traditional transmission lines could never carry the maximum output of both central generating stations and distributed renewables.

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As the electric power grid evolves, transmission lines need to be converted to electric powerways to optimize power flow. An electric powerway is a transmission element that offers impedance control, so operators aren’t limited to a single power source or size, a major limitation in today’s grid. Once implemented, electric powerways will allow transmission system operators to direct the flow of power from any point of energy generation to any point of energy consumption. With electric powerways, all lines will be able to operate closer to maximum capacity at the same time. Just as highways have optimized transportation, electric powerways will optimize power flow across the interconnected grid.

A key benefit of powerways is that they will not require a total overhaul of grid infrastructure. Instead, new components can be added to the existing infrastructure to modify them. Let’s take a look at the concept of a powerway, the innovations necessary for their implementation, and the benefits we’ll see.

New Components for Electric Powerways: SSRX & T-Caps

Converting transmission lines to powerways requires the introduction of several new components that will be used to optimize powerway impedance. Currently, the impedance of transmission lines is a fixed value based on wire size and line length. The impedance of powerways can be much more variable within the range specified by the system operator. Two devices should be installed along powerways, depending on line impedance: solenoid series reactors (SSRX) and high-current transmission-class series capacitors (T-Caps).

Solenoid series reactors (SSRX) are new devices used to reduce fault current and stabilize voltage. The impedance of short powerways can be increased during normal system operating conditions by installing SSRX at each line terminal. SSRX will further increase impedance when short circuits occur. This will stabilize grid voltage within eight milliseconds. This special feature of SSRX will enable renewable energy supplies to ride through fault conditions.

High-current transmission-class series capacitors (T-Caps) are used to reduce the impedance of longer transmissions line. Once inserted, T-Caps can be activated to reduce the impedance of long powerways, thereby optimizing power flow. When needed, T-Caps can be bypassed to return the powerway impedance to the initial value. T-Caps will be 10 KV, 2000 amp components, and will be located at several locations along a powerway. As a note, T-Caps are still in the design phase.

Once these devices are installed in existing transmission lines, the conversion to electric powerways will be complete.

Case Study: Metropolitan Area Transmission Lines vs. Electric Powerways

Consider, for example, transmission lines that power a metropolitan area. Transmission lines have been built from throughout the state and other nearby areas. Power transfer across the existing network of transmission lines is limited by the line that carries the most current.

Table 1 shows a model of the maximum power capacity of traditional transmission lines. The rating for each line is significantly higher than the actual load carried by each line. In this model, all seven lines can only ever transmit 63% of the combined rated capacity for all seven transmission lines serving the metropolitan area.

If Upstate Transmission Line 1 is out of service, then Upstate Transmission Line 2 is the limiting transmission line, carrying its maximum rating in amps. Maximum power transfer capability is still 63% of the total rated capacity.

In contrast, when transmission lines are converted to powerways, power transfer capability will be increased to 86% of the total rated capacity for all seven lines. Table 2 shows that the rating of each line remains the same, while the network load increases. The values in Table 2 are based on powerways that include SSRx and T-Caps.

The increase in power transfer capability of 3,200 Amps is equivalent to building two additional lines to serve the metropolitan area. Even when one line is out of service, power transfer capability remains at 86% of capacity.

Benefits of Electric Powerways

Electric powerways will provide major benefits for electric utility companies. Powerways will increase the capacity of current transmission lines by over 20%, allowing more power to be sent over existing lines. This eliminates the need to build new transmission lines and other infrastructure.

Energy from distributed renewable sources could be easily transferred once powerways are commonplace, allowing the energy from renewables to be integrated smoothly into the existing grid.

Electric powerways will also benefit the consumer by eliminating price spikes on the power grid because of the increased power flow capability across the grid. Interconnected powerways will optimize power transfer, because all lines will be able to operate at maximum capacity at the same time. Energy shortfalls, like that experienced by California residents in the summer of 2020, should become a thing of the past. Powerways will be able to move significant amounts of power among all connected parts of the grid.

Electric Powerways Will Efficiently Transmit Distributed Renewable Energy

Electric powerways will help prepare the grid for distributed renewable energy sources by allowing for more efficient transfer of power from location to location. While the current grid is designed to transmit power from central generating stations to major points of consumption, new electric powerways will allow power to be transferred among all locations where power is produced or consumed. Cities with abundant rooftop solar could transmit power within the city or to remote areas as power is needed. Power flow would be optimized everywhere.

If SSRX and T-Caps designs are optimized, prototypes are fabricated, and high power testing is completed in 2022, a demonstration conversion of a transmission line to a powerway can be completed as soon as 2024. Electric powerways will be a game changer for the electric power industry.

 

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Matt Chester's picture
Matt Chester on Mar 31, 2021

. While the current grid is designed to transmit power from central generating stations to major points of consumption, new electric powerways will allow power to be transferred among all locations where power is produced or consumed. Cities with abundant rooftop solar could transmit power within the city or to remote areas as power is needed. Power flow would be optimized everywhere.

Really exciting to see not only where the industry is going, but how utilities are recognizing the need to embrace and not fight that change

Bob Meinetz's picture
Bob Meinetz on Mar 31, 2021

"The electric energy grid is designed to transmit power from central generating stations, such as coal burning power plants, to areas of consumption, cities."

There's a reason: it's the most efficient way to distribute electricity to the most people.

"Transmission lines must be updated so that they are able to transmit power from various energy sources, rather than a single generating station."

Actually no, electricity doesn't need to be transmitted less efficiently. Let the people with whom distributed generation is "popular" pay for it - most of us don't need updated transmission, or want it.

 

Tony Sleva's picture
Tony Sleva on Apr 1, 2021

Thank you for the comment. You are correct in that transmission lines are highly efficient today; however, they are not transmitting power at their full rated capacity. Converting transmission lines to electric powerways will allow us to use near full capacity of the existing power grid to transfer energy to needed locations.  This will aid in the integration of distributed renewables, which are necessary as part of the solution to climate change. A major goal with electric powerways is to provide a path for backup power when renewable energy sources are unavailable. A second goal is to assure that the system remains robust and able to ride through storms and other naturally occurring events.

Bob Meinetz's picture
Bob Meinetz on Apr 2, 2021

Tony, there's no political, physical, environmental, nor financial basis for a national power grid. Transmitting intermittent electricity >1000 miles on even the most efficient HVDC cables will waste more energy than it delivers.

It's taking an already overcomplicated problem and making it more so - deliberately, IMO,  to exort more money from consumers.

"This will aid in the integration of distributed renewables, which are necessary as part of the solution to climate change."

There's no evidence to support that claim, and considerable evidence from Germany to suggest it's limiting progress. We've given the benefit of the doubt to wind and solar for over 60 years - no more time to waste.

Jim Stack's picture
Jim Stack on Apr 2, 2021

Thank you Tony. I have never heard of adding these items to make a Transmission line better. QUOTE=SSRX and T-Caps designs are optimized. This sounds like making a Smart GRID. 

Others seem to think the failing GRID we have is optimized even after we have had many big failures. I think it's about time we improved the GRID. 

Julian Jackson's picture
Julian Jackson on Apr 8, 2021

That's interesting. The issue I see is costs - I assume that these components are new and therefore both expensive and lack known reliability? So the grid operators will have to find the capital investment in some, and probably push the cost off onto the consumer? Obviously if they were widely used the unit cost would come down dramatically.

I'm not trying to be negative, but all technological innovations have downsides and I wonder what they are?

Tony Sleva's picture
Tony Sleva on Apr 9, 2021

Hi Julian, thanks for the comment. As you stated, there are always downsides to innovation, but I believe that there are more positives than negatives with electric powerways.

The electric power grid is a three machine system: east of the Rockies, west of the Rockies, and Texas.  During peak load conditions, a three phase fault on any 230 KV, 345 KV, 500 KV or 765 KV transmission line has the potential to cause another multi-state blackout.  My goal is to increase the robustness of the power grid so that wind turbine generators, solar farms and other renewable energy sources can ride through three phase faults. 

Any new elements that are added to the power grid will be tested in a high power lab before being placed in service at a demonstration project.  High power testing will be a challenge as surge testing and short circuit testing of new components that have never been manufactured before will be required, and will be costly.  Arrhenius testing will establish service life. My company is trying to minimize risks by including material scientists and others with specialized skills as team members.  (For example, electrical engineers understand E=IR, material scientists understand polymers, mechanical engineers understand thermodynamics.)

Another challenge is the way that electric energy is bought and sold.  Moving to the next generation power grid will require that billing strategies be changed from KWH billing to KW billing.  This will be an obstacle until customers understand the need for change.

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