Subterranean substations

Going underground in urban centres.

The biggest challenge of supplying efficient and reliable power in a bustling city centre is often in finding space for large substations, especially as demand for power grows. On one hand, local authorities’ planning departments are often protective of city centre sites, particularly those in historic settings, and on the other, the value of land in city centre sites for office or retail development often means that there are strong pressures to give land multiple uses.

One solution to make the most of a limited footprint is to dig down, placing the substation below ground level, which frees up the surface for other purposes while providing all the functionality of any conventional substation.ABB’s state of the art underground substation concept enables up to 98 percent of an installation to be tucked away below ground, with only cooling ducts and access routes visible above ground.

Hiding a substation in a city centre
Underground substations are not a new idea, with many already in operation at many sites worldwide. The experience of constructing such substations, together with knowledge of planning regulations has enabled ABB to develop its methodology. The approach means that ABB canintegrate a transformer substation into any urban environment while meeting and future-proofing customer needs.

Using this approach, ABB can hide a substation underneath a building such as a shopping centre, car park or sports stadium. Public spaces like parks, public squares, traffic roundabouts or intersections can seem untouched to the casual observer but below the surface, can be an essential link in a city’s power grid.An underground substation will accommodate transformers, GIS, automation, protection and control systems, auxiliary equipment, AC and DC distribution boards, batteries, ventilation, air-conditioning and fire protection systems.

Good planning for faster completion

Underground substations have little surface impact
When carrying out a construction project in any city centre, time is of the essence, with pressure to keep build times down and deliver projects quickly and to budget. With this in mind, ABB offers a modular approach that can be customised to meet the specific requirements of an individual installation.

Supported by comprehensive guidelines and sample concepts, ABB’s approach is based on the most important aspects of project execution. Running alongside this,3D simulations will iron out any issues with the design and layout of the substation long before the start of the construction phase. This approach cuts out the margin for error and ensuring that all aspects are properly considered, including space for cable runs, ventilation ducts and safety equipment.

Ventilation equipment is an area that is examined particularly carefully, with the temperature profile of the surroundings being balanced against equipment operation to size ventilation and heat dissipation equipment with ducts sized to keep air velocity and therefore noise emissions within permitted levels.

Finally, the load-bearing characteristics of the ground and neighbouring structure are considered as these may inform the design and layout.

Long-term operation
But the proof of the concept is in the longterm operation of a substation, which is why ABB’s approach takes account of reliability, redundancy, safety, operation and maintenance.

As equipment ages and ultimately reaches the end of its working life, access becomes ever more important, not least for the station’s largest items, the power transformers. Envisaging delivery and removal of bulk items, ABB’s modular approach takes account of transportation and access to replace equipment on all levels.

Like most substations, underground stations are unmanned in normal operation but their design must take account of human safety, which is why safety features such as escape routes, smoke-free zones and separation of fire loads with bulkheads are designed in.

With only two percent of a typical substation being visible from the surface, ABB’s underground substation solution keeps potential hazards well away from the general public. At the same time, it meets the most stringent requirements for power supply and delivers compactness, economy, reliability and safety.

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    A cross section through a typical substation
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