In May 2021, the UK’s National Grid announced that, in a world first, it was employing the large-scale use of power flow technology to unlock 1.5GW of electric capacity – which works out to be enough renewable energy to power one million homes. Here, David Wright, Chief Engineer at National Grid, gives Utility the low-down on the innovative technology, and how it’s enabling the transmission network to support more renewable generation and achieve the UK’s net zero by 2025 ambitions.

The technology in question, SmartValve, designed by US-based company Smart Wires, is an electronic device that actively balances power flows on transmission lines.

Mr Wright said that, as supply and demand on the transmission network changes, network power flows change, and circuits can become unequally loaded. This leaves some circuits reaching their maximum capacity and others well below their limits.

“Installing power flow controllers such as SmartValves allows National Grid Electricity Transmission (NGET) to provide the Electricity System Operator with equipment which reduces the network congestion that otherwise limits renewable generation. This is done with minimal impact on communities and the environment,”

Mr Wright said. “These projects are unlocking network bottlenecks and enabling 1.5GW of additional renewable power – 500MW of power flow across three boundaries.”

How it works

“Put simply, SmartValve can push power off overloaded lines or pull power on to underutilised lines. Power on a line depends on the line’s voltage and its current. In real time on the electric grid, the voltage of a given line remains close to constant, so the best way to change the amount of power a line is carrying is to change the line current,” Mr Wright said.

According to Mr Wright, this can be achieved by changing the impedance of a line. Mr Wright uses the following equation to describe the physical relationship: V=I*X, where V= voltage, I=current and X=impedance.

However, impedance is a combination of two things – resistance and reactance. This makes things slightly more complicated. In this case, where resistance relates to physical parameters of the line, reactance relates to electric/ magnetic parameters of the line.

“SmartValve impacts the reactance of a line by sensing the line current and injecting a voltage waveform in quadrature with the line current.

What this means is it adds a sine wave to another sine wave at a precise angle. This has the effect of changing the line’s reactance. These sine waves can be added in a way that increases the reactance or decreases the reactance.

This has the counter effect on the line’s current (since the line voltage is fixed),” Mr Wright said. “Power follows the path of least impedance. When SmartValve increases the line reactance (and therefore increases the line’s impedance), the line current reduces – this is because, relative to other electrically parallel paths, the path with SmartValve is slightly less attractive for power to flow.

“The opposite is also true – when SmartValve decreases the line reactance (and therefore decreases the line’s impedance), more power can easily flow along that path, which has the effect of increasing the current on that line.”

A ‘reimagining of the grid’

Mr Wright said this technology, or at least the foundation of it, has been in existence for over ten years in a different form (and at much lower power capacity) on distribution networks.

He said the scale of NGET’s transmission project is unprecedented, and that it is the ‘reimagining of the grid’ in action. By that he means that modular power flow control technology is the solution that will enable a rapid, low-cost energy transition.

“By installing SmartValves at five locations across our network, NGET is taking advantage of the modular nature of SmartValve and truly leveraging the valuable flexibility that this technology offers,” Mr Wright said.

“These projects usher in a new paradigm of planning and operating the grid: large-scale, wide-spread coordinated power flow control can unlock huge system efficiencies.”

A swift rollout where it’s needed most

Mr Wright said circuits identified as bottlenecks of renewable power flows resided in the north of England near Harker, Penwortham and Saltholme, reaching capacity while surrounding circuits were still below their limits.

This is because power naturally flows on the path of least impedance. The entire network can be blocked from absorbing power when even one circuit reaches capacity, because the strained circuit will overload.

“National Grid is installing 48 SmartValves across five circuits at three substations,” Mr Wright said. “Following these initial installations at the three sites, National Grid is looking to extend the capability at Harker and Penwortham later this year.

This could mean freeing up an additional 500MW of capacity, enough to power more than 300,000 homes.” According to Mr Wright, the installation process doesn’t take long overall, especially compared to traditional options,
going from groundbreaking to fully commissioned in less than a year.

“Devices can also be easily moved if needed – NGET actually did this during the construction process to manage the sequencing across various sites,” Mr Wright said. “Transferring installed devices from one site to another took only a week, which is incredibly fast for high voltage infrastructure.

“NGET has installed 12 SmartValves – six at Saltholme and six at Harker. A further 15 devices at Harker and Penwortham have completed Stage 1 commissioning and are waiting on specific system conditions to facilitate the completion of commissioning.”

It’s expected that all sites will be fully up and running by the end of 2021.

Addressing global energy system challenges

“A smart, flexible grid can reduce congestion (which has been caused by bringing on new generation in new locations compared to the way the grid has operated for the last 100 years), and can unlock capacity so that renewables that are  stuck in connection queues can quickly and cost-effectively get their electricity to large load centres,” Mr Wright said.

Mr Wright said that, upon achieving a very high penetration of renewables, the availability of flexible solutions on the grid can enable effective real-time balancing of intermittent renewable generation from a range of sources.

“Having direct control over the power flows on the lines themselves gives grid operators an extra degree of freedom that doesn’t exist today.

Today operators can ramp generation up and down and in some cases ramp load up and down (e.g. asking industrial users to reduce their use if electricity supply is low),” Mr Wright said.

“A flexible grid allows operators to use the power lines themselves to unlock a flexible, dynamic system that accommodates the needs of demand and supply in real time.”

Mr Wright said the use of power flow controllers across the Australian network in areas experiencing capacity bottlenecks is an innovative and relatively uncharted approach to real-time operations. Modular power flow controls can offer more flexibility when it comes to network planning and investment.

“Our recommendation is to explore how this flexibility can drive value for your business and your consumers and be open to new ways of quantifying this value,” Mr Wright said.

“We look forward to seeing large-scale adoption of this technology in Australia and understanding the specific use cases for which Australian utilities leverage these solutions. We look forward to sharing our learnings, and learning from Australian leaders as well.”

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