Thank you for your question regarding grounding for substations on high-rise buildings. It is our pleasure to help.
Grounding a high-rise building is both straight-forward, and complex at the same time. The chief concern is in protecting the people working in the building and especially those working in the substations; the second concern is in protecting the building itself. High-current electrical faults can easily heat the natural water found in concrete to the boiling point, resulting in steam which will destroy the foundations. We will discuss the two (2) main issues below:
The first issue is personnel safety. It is critical that a complete engineering analysis occur on the hazardous Step & Touch Voltages that will form within the substations. The proper placement of metal plates, the volume and placement of rebar within the concrete, along with a number of other factors will determine what the potential hazards to human safety will be within each of the substations. These tight-spaced substations often have walls that are within ‘touching’ distance of transformers. This means that personnel can touch both a transformer and a wall at the same time, this is the most hazardous situation possible, and it should be carefully analyzed to ensure proper safety. It may be necessary to add some copper conductors into the concrete walls and floors, in order to reduce the differences in potential within the substations. This analysis also needs to occur for the office spaces adjacent (side to side, and up and down) to the substations, as these spaces will also have an extra exposure to electrical hazards.
The second issue is in protecting the building itself. Many times the foundations for these buildings are the key to providing effective electrical protection. Do you know if they are planning to use a vapor barrier to protect the concrete? If so, your job just got much harder. The ultimate goal is to ensure that there is a proper and effective metallic path from the foundations all the way up to each and every floor of the building. Copper is at least 12-times more conductive than steel and is 250-times less magnetic. Having a solid copper path from the substations all the way down to the buildings foundations is critical. While steel is conductive, the impedance issues that can build up as electrical faults try to clear your building will only be compounded by the magnetic properties and relatively resistive nature of steel. We typically recommend that the pilings in the foundation have copper conductors added to them to ensure an effective path to earth that is separate from the building steel. If your substations have Neutral-Ground-Resisters, it may be important to provide dedicated grounding electrodes specifically for this purpose.
Another factor that may be of importance is the Electromagnetic Interference (magnetic fields and electric fields) that can form within the building steel. This can severely impact computer operations for your tenants, and should also be considered when designing the structure. Also, have you considered lighting protection issues yet?
The subject of grounding high-rise buildings is really a very complex issue. You will need good soil resistivity data and several computer models in order to properly design your grounding systems. The design will include bonding of the steel throughout the entire structure, the addition of dedicated copper paths from the substation to the foundation’s pilings, additional copper grounding within the walls and floors as needed to eliminate hazards, and the addition of dedicated grounding electrodes to reduce current loads within the structure.
E&S Grounding Solutions is of course more than happy to help you with these critical engineering functions, but if not us, please get someone with the proper engineering tools, software, and experience to help you. Feel free to call one of our Engineers and they will be happy to discuss your project with you.
The Engineering Team at E&S Grounding Solutions
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