Transmission flow control gets smarter

National Grid Electricity Transmission (NGET) has awarded a five-year framework agreement to US–based power flow control technology company Smart Wires. This is expected to help decarbonise the UK electricity grid by enabling greater volumes of renewable power to be efficiently transferred to customers.

NGET will use modular power flow control technology to increase power transfer capability by making better use of its existing network. As the generation and demand connected to the network changes, network power flows change and circuits can become unequally loaded. Some circuits reach their maximum capacity while others are well below their limits.

Installing power flow controllers allows NGET to provide the Electricity System Operator with the tools to quickly reduce the congestion that limits renewable generation, with minimal impact on communities and the environment.

NGET will proceed with five installations in 2020. These projects are anticipated to increase boundary capabilities by 1.5 GW in total across three boundaries.

Modular technology Smart Wires power flow control devices allow utilities to increase the efficiency and resilience of the infrastructure. The technology’s modular nature means it is quick to install and move around, thereby providing valuable flexibility. NGET can adjust the roll-out of the technology in response to network needs as they develop.

The centre of the Smart Wires technology is its modular power flow control device – the SmartValve. (Figure 2), a single-phase, modular static synchronous series compensator (M-SSSC). It is a solid-state synchronous voltage source that injects a controllable voltage in quadrature with the line current. It employs a series of voltage source converters which consist of IGBTs and a DC link capacitor. The device has bypass capabilities for protection and control. The principal components of the bypass are the normally-closed mechanical contactor (vacuum series link – VSL), the silicon controlled rectifiers (SCRs), the metal oxide varistor (MOV) and the differential-mode chokes (DMCs).

Five projects

A total of five projects will be installed in 2020. These projects will contain a total of 375 MVAr of power flow control capability resulting in an increase in boundary capabilities by 1.5 GW in total across three boundaries, facilitating the increased power transfer of 500 MW from Scotland to England. NGET see numerous other opportunities across their network to employ this type of technology over the course of the framework agreement timeframe.

Smart Wires says that its technology can unlock more system capacity at a lower cost than legacy solutions. And once installed, legacy solutions cannot be moved or modified quickly enough to match the pace of change affecting today’s network. They therefore sometimes can be over-rated, compared to the initial requirement, or need replacement if the network changes further.

Smart Wires’ modular design is said to be a major advantage, making it easy to scale appropriately, providing great flexibility, both technically and in terms of scaling of the investment in response to changing system needs. The technology is also said to provide several additional advantages compared with legacy solutions including reduced substation footprint and digital control.

National Grid

National Grid owns and operate the electricity transmission network in England and Wales, with day-to-day responsibility for balancing supply and demand. National Grid also operates, but does not own, the Scottish networks. The network comprises approximately 7200 km (4474 miles) of overhead line, 1500 km of underground cable and 342 substations.