ELECTRICAL SUBSTATION DESIGN
Have you found yourself responsible for designing an electrical substation and you’re not exactly sure how to account for all of the details? Maybe you’re a brilliant engineer (but don’t have a lot of experience in electrical substation design) and the client and construction company are depending on you. Do you need to know the difference between an electrical bus and a switching station as it applies to electrical substation solutions? Well, we’ve put together some information here to help give you a better understanding of the many things you’ll need to account for in your design.
First and foremost, please know that we are here to help. We speak your language. From ASCE and IEEE standards to RUS (Rural Utilities Service), we’ve got you covered. Don’t hesitate to click on our contact us link. We’re problem solvers, and we’d love to help you design your substation—as well as procure the needed components. And we’d like to do all of that on time and within your budget.
As in most designs, form follows function. And the same concept is applicable to electrical substation design. First, we have to ask, what is the main purpose of a substation? What does an electrical substation do? If the idea is for high voltage power to come into the substation and a lower voltage power to leave it, then the elements within it must be assembled to make that happen. Each item plays a key part in the transfer and control of the power. From the point power lines come into the station to the point lines leave the station, we must define the needed components.
The best first step in making a plan for your substation layout is to create a one-line diagram. This is a drawing that shows the progression of power from the incoming supply lines through the switching and protection elements and out to the outgoing transmission lines. It is where most utilities and engineering firms begin. The one-line diagram allows you to simplify the plan for the needed lines, switches, circuit breakers, and transformers that will be required to ultimately build the station you need.
PARTS AND COMPONENTS
Most commonly, electrical substation lines will have both a disconnect switch and circuit breaker. However, sometimes only a switch or circuit breaker is all that may be needed, depending on the function of the substation. A disconnect switch can create isolation as it can’t interrupt load current. Another device, used to interrupt fault currents automatically, is a circuit breaker. It can be used to switch loads on and off or cut off a line when power flows in the wrong direction.
Current transformers are used to detect a large fault current flow through the circuit breaker. A trip of the circuit breaker can be caused by the magnitude of current transformer outputs, and can result in a disconnection of the load supplied from the feeding point. This is advantageous as it isolates the fault point and allows the remainder of the system to continue operating.
Lightning and surges within overhead transmission lines can cause insulation failures within substation equipment. However, substation equipment can be protected by line entrance surge arrestors. In designing your substation, you’ll want to account for how to best protect equipment and reduce the outages caused by failures.
Once you’ve accounted for the switching components, the line or lines are connected to a bus or buses. These buses are usually set in multiples of three. This is based on the universal use of three-phase electrical power.
Since the cost and reliability of a substation can depend on the arrangement of buses, circuit breakers, and switches, you’ll want to be very careful in your planning stages. You should consider a setup that accounts for the failure of one circuit breaker not interrupting the flow of power to others. This can be done by adopting a ring or double bus setup. You should also account for the fact that parts of your substation will need to be able to be de-energized in order for repairs or maintenance to be done.
Once you’ve planned for your buses of various voltage levels, transformers can be placed between them. These transformers will need a circuit breaker in the event of a fault or short circuit.
Transformers, circuit breakers, and switches can be connected by air-insulated bare conductors on support structures. The lightning surge voltage rating and the system voltage affect the air space needed for their use. Metal-enclosed switchgear can be used for medium voltages with no live conductors exposed. For high voltage situations, the space required around the live bus can be reduced by using gas-insulated switchgear. Pressurized tubular containers, filled with sulfur hexafluoride (SF6) gas, have the bus and apparatus built into it. This allows the container dimensions to be reduced since the gas has a higher insulating value than air. Sometimes, instead of SF6 gas, a tubular container apparatus can use transformer oil, porcelain, paper, or polymers specially designed for that function.
The structure of electrical substation designs can vary according to location. Again the need and situation will dictate the materials. Form will once again follow the needed function.
Above ground, outdoor substation structures can include tubular metal, lattice metal towers, or wood poles. In some suburban locations, the appearance may be critical, so the design must take this into account. Some substations may need to be indoors and utilize metal switchgear at lower voltages or gas-insulated switchgear for higher voltages.
You may also be designing your substation to fit within a building, as in many urban situations. Within city centers, without a lot of available land, there may be a need to build the substation below ground. Underground substation design can be challenging but not impossible. An underground location can reduce the space requirements. And since more than 90% of the components will be out of sight, the surface area can be used for other purposes such as a park, parking deck, or even stadium.
In addition, your substation will always need controls to operate the circuit breakers in the event of a component failure. You’ll want to consider your Supervisory Control and Data Acquisition (SCADA) options for your substation. Standardized protocols such as Modbus, DNP3, and IEC 61850 are commonly used to provide access to remote control centers for power-system automation.
HERE TO HELP
If all of this is overwhelming, we understand. There are so many details to account for when designing an electrical substation. That’s why we invite you to lean on us. Let us help you. Our experience in substation design and packaging is second to none. Let’s connect and see how we can help you. Reach out to us via email or by phone. We provide substation solutions.
We’d love to help with your substation project. Use the contact us link or give us a call at (877) 324-0909.
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