What is a Substation and How Does it Work?
6.29.2018
What is a Substation and How Does it Work?
How Can I Identify a Substation?
Substations are usually easily identified because they are surrounded by a fence. Typically gray in color, substations are used to either step up or step down electricity. Electricity converts from transmission to distribution in a power substation. Power must be stepped-down to be useful in a home or business, which can happen in many phases. Substation transformers can also step power up to a higher voltage allowing it to travel farther. As an integral part of the electrical system, here are some things to know about power substation transformers.
Substation Applications.
Application - The application in which a substation will be used is one of the most important things to know as it affects many aspects of the build. Depending on whether the transformer will be used for a Generator Step-up (GSU), for a furnace, to run motors, or for your standard step-down application, all play a role in how the transformer is designed to ensure that you will get the most life out of your unit. T&R Electric's experienced sales staff, and team of engineers, will walk through your needs with you, discuss how you plan to use the transformer, and together we'll make sure you have the correct unit for your application.
Protection Devices for Substations
Oftentimes there are several different types of protection devices and schemes in place within a substation. Some aren't even attached to the transformer itself. A couple of the more common protective devices and schemes are surge arresters and differential protection. Arresters are connected to the conductor before it enters the substation; the arrester is also connected to ground. It works by diverting the energy from an over-voltage transient to the ground, thereby avoiding the transformer, should a surge occur.
Differential protection, on the other hand, works on the principal of comparison by using relays that operate when the phase difference of two or more electrical quantities deviates from (exceeds) a predetermined value. This type of scheme often requires the use of current transformers (CT's) for monitoring. In either case, T&R can help you outfit your transformer to fit your protective needs.
Base Load and Max Load
Substation transformers can be designed and constructed to handle a larger load during times when an increased demand is present without exceeding certain temperature rises. A transformer generally has a "base" KVA rating (capacity rating), but in addition, it can be equipped with additional cooling means, both within the windings themselves as well as external cooling, to allow for a larger capacity to be achieved. For example, a 10000KVA transformer (base) with a 55C rise can be built to have ratings of 10000/11200/12500/14000 KVA; 10000 and 12500 are at 55C rise while 11200 and 14000 are at 65C rise. The 10000 and 11200 KVA ratings are achieved by simply accounting for a difference in temperature rise during the winding phase.
The 12500 and 14000 KVA ratings also take temperature rise into account, but in addition, they include forced air cooling. Forced air cooling is achieved by adding external cooling fans to help cool the transformer oil and stay within the defined temperature rise limits. If necessary, additional cooling radiators can also be added to the transformer tank to aid in circulation of the oil. It is important to note that the transformer must be specifically designed to handle increased demand, as simply adding more cooling means is not enough. In other words, if you are anticipating future demand increases, it is always best to let us know ahead of time, so we can get you exactly what you need!
Switching or Regulating Voltage
LTC - A Load-Tap Changer ("LTC") is an accessory that allows the substation to "switch" or "regulate" voltage while under load (i.e. the substation transformer does not have to be de-energized to switch voltages). LTC's are an integral part of many electrical systems and, similar to regulators, work on the make-before-break principal. With this type of accessory there are many variations of components and features available to choose from allowing the customer flexibility.
T&R Electric can assist you in your LTC requirements, and help determine what will work best for your application. It is also worth noting that since LTC's work differently than your typical de-energized tap changer, the oil test results, particularly the Dissolved Gas Analysis (DGA), of a substation with a LTC may differ from those of a unit without a LTC. T&R Electric also has a full service lab, with oil testing, and the professionals on hand to help you understand your oil samples.
What Size Substation Do I Need?
One of the most common questions we get asked is if T&R Electric can provide a substation transformer that will fit the current set-up. The answer is yes. Whether you have a top/top, top/side, or side/side bushing configuration will make a difference on how the wires are connecting to the substation, and will affect your space configuration. In addition, if you know the size of the pad that your substation transformer sits on, what the current dimensions are, and if there are any size restrictions, we can ensure that your reconditioned or rewound transformer will fit.
With our newly expanded substation shop T&R Electric has over 40,000 square feet dedicated to rewinding and reconditioning substation transformers. From 5 MVA up to 30 MVA, let our experienced sales staff and engineering team work with you to build a substation that meets your exact needs. Call us today at 800-843-7994 or visit us online at www.t-r.com.
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