Why build when you don’t have to? The substation is a most important piece of `land’ that houses very critical equipment: the power transformer that simply makes our lives livable. We are addicted to electricity and our addiction deepens by the day, especially for our children. Nowadays, if it weren’t for electricity, many would not be able to drive, charge their phones (imagine not checking your Facebook page for a few hours; how are you going to survive!?), wake up on time for work, check the time, and get through a never-ending list of day-today activities that rely on having access to electricity.
In many areas, new substations may be needed to meet a forecasted peak load that may – or may not – occur for a few hours during the morning or evening (depending on whether the system is summer or winter peaking). For this reason, there has recently been a regulatory push in favour of including Customer Sited Solutions (CSS), such as solar PV, energy storage, and distributed generation, into the grid to meet the forecasted load for those few hours.
This solution will eliminate or defer the need for a substation; as such, the entire utility structure is reforming as the customer transitions from being a passive user to an active power producer. [quote]
Making informed decisions on whether to build or not to build
The journey begins with the X/Y phenomena, where X is the system loading (transformer or transmission/ distribution line) and Y is the capacity/ ratings of the system; if X/Y=1.0, then load = capacity, no work needed; if X/ Y>1.0, load exceeds capacity and load relief is required.
There are two more steps needed before deciding to build a substation: performing an efficiency/ losses/theft audit to ensure that the current system is efficient, losses are acceptable and power theft is manageable. The final step is to ensure that the current load is accurate; imagine the embarrassment of building a new substation based on using inaccurate load data.
Substations are often built to replace outdated aged infrastructure that would be more costly to maintain. The new station should offer more capability and should be based on the latest standards and specifications, mainly IEEE Power Substation standards that govern the equipment rating, substation configuration and key components, i.e. grounding, bus structures, seismic design, fire protection, containments and control of oil spill, security, gas insulated substations, breakers, disconnect switches, communication, and more. Some utilities may have more aggressive standards than IEEE to ensure a reliable system, somewhat similar to OSHA (occupational safety & health administration) standards that are responsible for worker safety and health protection, where utilities may have aggressive standards to further protect their employees.
Load growth is a very common driver for building new substations: this can be as extreme as exponential load growth seen in Dubai, or typical regular load growth, which is comprised of three categories: natural load growth, which occurs when buying new equipment, like larger TVs, enlarging the family, and acquiring items associated with raising a child; new business, such as new restaurants, expanding residential areas, new high rise and commercial buildings; and major new events that result in heavy electricity usage, such as film festivals, carnivals, international sports contests, the discovery of a certain mineral or oil, etc. Load growth is the main reason behind the need for new power plants, transmission substations, distribution substations and circuits.
Where, when and what to build
Now that the planning group, financial professionals and regulators have come to the consensus that a substation is needed, the next steps are:
• Location: closest to the load centre is ideal, as that way losses will be reduced, distribution lines will be shorter, minimizing voltage drops and making restoration quicker after faults, not to mention reducing the cost.
• Availability of the source, i.e. proximity to the transmission source and proximity to the generation system ;if building a transmission substation; the critical path is finding the balance between being close to the load centre and/or being close to the transmission source.
• Nature of the load served and location will dictate the substation configuration: underground versus overhead design, distribution type, i.e. radial, autoloop, network or a mix. Also the reliability required, i.e. n-1, n-1-1 or n-2 (n refers to normal, so n-1 means that the new station can survive losing one major component without resulting in any overloads/voltage issues). In some areas, the reliability is dictated by the total MW per square miles. This goes back to the desired reliability level and identifying common mode of failures.
• “Not in my back yard” is universal; regardless of how rich or poor residents are, they do not like to see overhead lines; a cost benefit analysis is needed since overhead lines have higher capacity, and are cheaper and quicker to restore than underground lines.
New substations must be ascetically acceptable, they should where possible blend in with the environment, have the same façade as nearby buildings to fit in. The point is: think of your substation as a chameleon. Planting tall trees around the substation is a common method of improving its appearance.
Due to property being scarce, there has been a shift to install substations underground, such as under a park (completely invisible from the public), similar to the subway system; however, flood mitigation and fire protection become critical factors.
You are probably accustomed to seeing air insulated substation designs; in order to mitigate the public’s opposition to build and the space limitation, gas insulated designs are now utilized as well as building on multiple floors. The electric bus design (straight, ring, etc.) is very important in the early design of the substation.
Another important cost related question is what accommodation is left for the future, including whether to allocate space for a future line/ transformer, allow for the building of spare conduits, such that the street need not be dug up during cable failure to remove the damaged cable before installing a new one.
Another common location is building substations in the first floor of a multi-story building; the main disadvantage is the tenants’ opposition to living or working in a building that houses high voltage equipment, where utility workers and/or contractors will be frequent visitors, as well as the threat of electric fires and environmental spills.
If the load growth is not significant, then compact substations may be utilized; compact substations resemble containers, which the public is accustomed to seeing. The transformer, switchgear and other key equipment are housed inside the container.
Never forget the details
There are other matters to consider when building a substation and distribution systems. The proximity to utilities, including sewer lines, water lines, telecommunication lines, and gas lines. Access to the substation that allows large equipment around the enclosure during construction, and when planning for replacements during emergencies. Furthermore, consider communication equipment, oil pumping plants, permits and zoning.
Mother Nature is a critical player in the design, where substations planned in flood zones must be elevated; an area with significant lightning must have ample lightning protection. As such, the level of protection needed is also key in the design. This is related to the utility design: relays, relay communication, first line, second line defence relays and back-up relays.
It is important to recall that substation equipment, mainly transformers, are usually built to the utility’s specific standards/ specifications, thus there is a long lead time, coupled with the time needed to acquire property, environmentally cleaning it up, getting all the permits and redesigning the transmission supply and distribution routes.
With this in mind, it is ideal to make a decision sooner regarding whether a substation is the way to go or not and this is when the load forecast becomes handy. Nowadays, the station also needs to be designed to accommodate renewable energy resources (solar farms, distributed generation, energy storage batteries, etc.), which is mainly tied to voltage control equipment and protection equipment. Also, due to the push for the future smart grid, how smart do you want your station to be?
In conclusion, before you choose to build, make sure you have: accurate load forecast and updated ratings, cost effective location from a transmission and distribution perspective (source versus load), reliability goals, level of smartness desired, desirable renewable accommodation level, acceptable efficiency/theft level and losses, expected level of opposition, and required outreach, Above all, remember you are building the most important piece of land on earth, so don’t expect it to be an easy project. ESI