Rapid recovery is increasingly important for grid operators. With advanced developments, like compact power electronics and resilience concepts, solutions are now in hand that are small enough to be mobile and still provide safe, timely and location-specific responses to improve grid stability.
By Alexander James
Changes in the energy landscape are presenting challenges in transmission and distribution. Increasing urbanisation and widely distributed renewable resources are forcing operators to manage scenarios not conceived when aging grids were designed and built. Congested urban landscapes make the acquisition of land, securing permits and access for new power lines or substation infrastructure difficult. Major infrastructure projects further face high capital costs and long development timeframes that may mean they are superseded by new demands before being commissioned.
Where conventional asset development pathways fail to keep pace with the demand for a more robust and flexible grid, mobile substation technology offers a solution to bolster transmission grid nodes and build in resiliency.
Making transmission mobile
Breakthroughs in solid state technology and high-voltage equipment, such as switch gear and power transformers, are enabling far more compact power systems. For mobility, structural and operational integrity need to be maintained during transport. To minimise mechanical stresses on pressure systems during transport, Siemens Energy developed a single structural system design with elements, such as high voltage bushings for gas insulated switchgear, rotatable and foldable for transport. This has resulted in rapidly deployable, containerised, modular units.
Siemens Energy mobile static synchronous compensator (STATCOM) technology is around 50% smaller than conventional Static Var Compensator designs, making it highly mobile. Major US utility Dominion Energy deploys this technology during critical periods, such as maintenance outages or following catastrophic events like hurricanes or floods. Once the emergency period has elapsed and power restored, the asset is relocated or returned to depot ready for when it is next needed.
STATCOM keeps the grid stable during disturbances by providing fast and controlled reactive power. Based on Modular Multilevel Converter architecture, it uses Voltage-Sourced Converters to provide a nearly perfect sinusoidal voltage waveform and generates significant capacitive or inductive output current independent of the AC system voltage. This makes low-frequency harmonic filters, which were often used in earlier designs, superfluous and substantially reduces overall installation size.
Helping transmission line project
Dominion Energy deployed a mobile substation to support its operations during the Cartersville high-voltage transmission line rebuild project in Cumberland County, Virginia. Typically, rebuild projects require a temporary transmission line to provide electric service to nearby communities during construction. For the Cartersville project, difficult terrain prompted the use of a mobile solution, avoiding the need to build a temporary transmission line and saving $4M in project costs. Originally part of Dominion Energy’s resiliency strategy, the substation was the first 230/115kV mobile installation in North America.
Siemens Energy mobile resilience transformers were developed in collaboration with Consolidated Edison (ConEd), the utility that covers locations including New York City, as a part of the Siemens Energy PRETACT® concept. The PRETACT resilience concept was developed as a proven solution for bypassing transformers for emergency or maintenance purposes. Features include plug-in bushings and cable connections along with the possibility for different voltage levels and configurations. As compact, lightweight, fully assembled single-phase units, the transformers are readily deployed and use environmentally friendly MIDEL ester-based fluid.
As part of a US$1 billion grid resiliency plan, ConEd commissioned six mobile substations, each with total transport weight less than 100 tonnes. If the configuration is known in advance and the mobile substation can be prepared and pre-configured, units can be installed and commissioned in just a few days.
National Grid SA, grid operator in Riyadh, Saudi Arabia, has deployed portable power technology including mobile substations from Siemens Energy with a capacity and rated voltage up to 502MVA and 420kV. These enable bypass of any of the transmission system’s 380kV substations and connect the 380kV grid with any of the three other grid voltage levels. In the event of a failure or scheduled maintenance work, each unit can be delivered to site on six trailers, including GIS, transformers and all necessary auxiliaries, control, and protection systems.
Portable Power Solutions built within a shelter, or so called “E-Houses”, are meant for semi-permanent installation and are a way to quickly add new assets to a grid. They transfer a large amount of site work to the factory environment, saving up to 30% in substation construction time and minimising human, technical and construction risks compared with conventional on-site works.
Ideal for mining or other industries that need to operate for a few years and then move to a new location, these systems are also being adopted in regions where the grid is expanding rapidly, or its characteristics are changing. For example, Siemens Energy has delivered more than 40 mobile substations to Algeria over the last decade as part of its grid expansion, most of which will remain in operation at the same location for several years as the grid matures. Other regions may be faced with environmental challenges, such as extreme seasonal weather, that require timely substation installation for a short duration, for example the short summer season in parts of Canada or Russia.
The future is mobile
Portable power solutions are proven in numerous utility and industry applications. Using mobile solutions, operators can quickly restore power after a substation failure and avoid disruptions during grid maintenance and upgrade. Moreover, the technology offers an ideal route to rapid grid reinforcement when networks are expanding quickly or handling seasonal peak loads.
September 14, 2020
Alexander James is a freelance journalist.
Combined picture credits: Getty Images, Siemens Energy