Power Utility in the Data Center

By Dan Fanning

image-for-data-center-articleThe power for a data center, as with everything else, comes from its electric utility. The utility generates power from any number of burning and turning means. The utility then distributes the power across the transmission network to its customers. Our concern at EDI focuses mainly on electrical capacity and the reliable delivery of the power the client needs to run the data center. In this article, we are not going to concern ourselves with specifics of generation, transmission or other “how it’s made” type of details. Instead we will be looking at the role of the utility transformer and its effect on the building that uses it. For more information on electrical distribution, check out these links:

Building distribution and High voltage transmission

EDI’s job is to communicate with the utility and conduct research on behalf of our client, to ensure that the client receives the most reliable power they can afford at the capacity they need. Communication and research typically happen when a client is seeking a new location for a data center and has hired us for a feasibility study, an assessment or a new design project.

Transformers are essential for the transmission and distribution of electricity. A transformer “transforms” the primary voltage into a less lethal and more practical secondary voltage. So let’s say we look outside in your neighborhood and find that the primary voltage is at 4,160v from the electrical pole to the transformer. That voltage is not so great for charging your phone. It does have beneficial transmission qualities for the utility, however. The transformer in your neighborhood “transforms” the 4160v to 240/120v that is present in your home electrical panel. If you want to know more about “transformation,” check out this video.

The utility transformer at a building does the same thing. It transforms transmission level voltages down to useable secondary voltages. Transformers are sized in Kva. The sizing of a transformer directly relates to the amount of power that will be available at the buildings electrical service. Large consumers like data centers require large transformers. More often than not, we are called out to look at a commercial office building that a client is interested in modifying into a data center. The utility transformer at this site more than likely will be undersized for a data center application. Even if the site has a large electrical service, it can be misleading to the layman. The utility transformer is normally sized smaller than the service. This condition could be the bottle neck that will disqualify the site for use as a data center. Let’s assume the transformer is too small for the design load for the proposed data center. Using a well-timed feasibility study, we will discover this condition in advance of lease or purchase negotiations.

But can’t the transformer just be replaced? Of course it can, but at what amount and at who’s expense? This is tricky. The utility will rely on electrical load data over the past few years to determine the necessary size of the transformer. That data will be based on the site’s old application as an office.  The utility will not be inclined to spend money on a new transformer based on this data. For a data center electrical load, we typically provide a 10-year growth plan that has a Day 1 design load that is smaller than the 10-year future load. We have to convince the utility to disregard the current data and upgrade our transformer based on our projection and time line of the future load.

Using our national transformer replacement history in office building conversions, the utility will install a transformer based on 40-60% of what the ask is. If the load grows, most utilities are comfortable running the transformer at 120% or higher than its design rating. As data center designers, we’re not keen on this approach. Our job is to present a viable case to the utility that we actually need the power for which we’re asking. Some of the tools we use to do this include a load study and a growth analysis tied to a time line. If we are successful, best case is the utility will upgrade the primary side and transformer at no cost to our client. The “primary side” is the name given to the lines from the utility lateral to the transformer, which are all owned by the utility. We are now only responsible for the “secondary side.” The “secondary side” is the name given to the lines owned by the building. They are run from the utility transformer into the main electrical service section of the building. If our case isn’t strong enough, we could end up paying all of the cost or a split between the utility and the client for the replacement of the transformer and the primary.

During a feasibility study, we collect the information obtained through our communication and research with the utility.  We then compile the data into a report that describes the utility’s capability in the area, how it will affect the client’s design and budget, and a Go/No Go type decision for the proposed site. If we get past the utility transformer, the rest of the study focuses on how closely the proposed building aligns with our client’s project needs and requirements.