Is there a silent threat in your data center power distribution system?
You’re not worried – you did everything right. You spared no expense in the electrical design of your data center, investing in robust redundancy and back up generation systems. You even included Level 4 commissioning to make certain your design was installed properly and 100% functional. In fact, in the first few years the system proved itself; there were a few sustained outages and those beautiful backup generators roared to life and carried the data center load like Atlas must have carried the world on his shoulders. It’s a work of art, if you stop and think about it. You sleep well at night.
IT upgrades may have unintended effects
Still, time goes by. Your IT team upgrades to new servers and continues to expand the IT load, and a hidden threat lurks. It’s not a denial-of-service (DoS) attack, or an electrical fault somewhere in the design. It’s nothing you can see. And then one dark and stormy night you lose the utility; your system transfers the IT load to your gen sets, which quickly fail and trip off line. Data center down! It’s your worst-case scenario. Your management team wants heads to roll, and neither the generator manufacture nor your electrical design consulting engineers have any solid answers to tell you what happened.
Capacitive loads and power factor
Here’s the thing: today’s harmonic corrected IT power supplies are capacitive when they are loaded under their rating, which often happens. The cumulative impact causes something called “leading power factor”. Generators can be quite sensitive to leading power factor, and as IT equipment is upgraded over time, leading power factor can reach levels where these generators trip off line when connected to the IT bus. If there is a UPS in the power path between generator and IT load, the UPS acts as an effective shield from leading power factor. But when the UPS is bypassed – either automatically or manually using either a static or maintenance bypass – the generator is forced to supply the leading power factor of the IT load. This causes a fault condition at the generator, triggering it to shut down, often at the worst possible time.
The good news is that even though there is a great deal of confusion about how to evaluate this risk, (and a superficial analysis of a particular design or installation is likely inaccurate), there are several ways to mitigate the risk and make sure your data center is always up and running. For example, power correction systems and active harmonic filters are a very effective way to deal with power factor. These systems monitor a distorted electrical signal, determine frequency and magnitude of the harmonic, and then cancel those harmonics by injecting an opposing current. Active Harmonic Control is just one of the benefits of a power correction system. Maybe the most important benefit is once again sleeping well at night, knowing you’ve taken measures to address leading power factor before it can create any damage.
In the next blog article, I’ll cover exactly how a good power monitoring solution can leverage metering technology to meter the IT load and create an alarm when generator load conditions run the risk of instability.
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