Data Centers

What to look for in a data center backup generator

Backup generator sets are massive, complex engineering marvels that data-center owners must have, but hope they will never need. Here's what you should know before buying one.

Cummins QSK 95, which is definitely not your average diesel generator set.
Image courtesy of Cummins

Managers of data centers offering colocation and cloud services sign contracts guaranteeing 100% uptime. Most engineering types would say that's impossible; however, that kind of guarantee is the cost of doing business in today's market. If the service is anything less than 100%, clients get substantive refunds, and the data center loses credibility.

That could explain why data-center operators will spend millions of dollars on backup power-generation equipment, which more often than not amounts to diesel generator sets similar to the Cummins model pictured above.

To learn more about how these monsters work, I contacted the Cummins Power-Generation Business Unit, which is the division that builds generator sets of all sizes, from Onan RV models on up. At the division headquarters in Minnesota I met Richard Hallahan, Technical Marketing Manager for Data Centers and a certified professional engineer, and he ushered me into a high-tech conference room and asked how he could help.

Buying a backup generator for a data center

My first question for Hallahan: how does one go about buying backup generators for a data center? Hallahan says the first step is determining what power-distribution infrastructure will meet the data-center's needs. To accomplish that, Hallahan recommends:

  • Understanding the raised-floor area, heat load, and square area or number of racks, because that will help estimate the facility's total power consumption needs. The outcome will tell you the approximate size of the required power system.
  • Defining the chosen reliability architecture for the facility, using guidelines such as the Uptime Institute's tier levels to drive the power-system architecture decisions. This will determine how power gets to the critical loads.
  • Implementing standard power-distribution system architectures, especially when paralleling multiple generators, because this will increase reliability and enhance serviceability.

And Hallahan should know — before moving to Cummins, he helped Target get its biggest data center in Minnesota "construction certified" by the Uptime Institute.

What to look for in a backup generator

My next question for Hallahan: you can't test drive a backup generator or kick the tires, so what's important when shopping for a backup generator? Four things according to Hallahan:

High-horsepower generator sets: Data-center generator sets should be designed specifically for this task, and that includes getting to full speed in seconds. It also means being able to accept full-power loads without affecting the load performance.

I have military-service experience with generator sets, and the above requirements are not trivial. The engine coolant must be kept at operating temperature. Special lubrication pumps need to periodically shove oil throughout the engine so bearings are riding on an oil film rather than metal-to-metal contact.

Something I did not know: Larger generator sets have multiple starters to rotate that much mass quickly when starting. Hallahan adds being able to maintain (adding oil, changing fuel filters, etcetera) a running, fully-loaded generator set is also vital.

Power distribution: Tier rating and power requirements will determine the controls on the generator sets. Redundancy and reliability of the control systems that switch generators online or control several generator sets running in parallel are critical.

Digital controls technology: Modern generator sets have digital controls. Hallahan says make sure digital controls are not an afterthought — you should include digital controls in the initial design of the power-generation package.

Remote monitoring and control: Having digital controls allows remote monitoring and control capabilities. Data-center operators can observe engine and alternator data, control system status, power-transfer status, power-transfer connection status, and load levels without leaving the NOC.

Cummins new generator set

While touring data centers, I have seen 1.5 megawatt generator sets and thought they were impressive. Cummins is introducing a new model: the QSK 95. Specs for the QSK 95 are: 16 cylinders, 95 liter, 4,000 horsepower. The alternator output is 3.5 megawatts. The generator set at the beginning of the post is a QSK 95. For some perspective, the gray control boxes on the alternator (right side) are at eye level.

On November 5th there will be an online interactive session about the QSK 95 generator set, where Cummins experts, including Hallahan, will be available to answer questions. If you're interested, register for the event.

About Michael Kassner

Information is my field...Writing is my passion...Coupling the two is my mission.

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