Greening the data center: DC power basics


There’s been a lot of discussion recently about using DC power distribution to “green” data centers and save energy. In this post, I’ll provide a primer for the components of a data center DC power system and a view of how they connect and work together.

The first item is the DC power plant itself. The power plant typically contains the rectifiers, the controller, the low voltage disconnect (LVD), the connection for the battery string, and possibly a CEMF cell. The rectifiers are the heart of the system, converting AC power to DC. The rectifiers are connected to the load and the battery string with a common set of bus bars. The LVD allows the controller to disconnect the batteries to prevent damage to them by over discharging. Another key feature of the LVD is, should the AC power be down long enough to discharge the batteries, it allows the batteries to partially recharge before reconnecting the load. Among other things, this puts far less stress on the AC power than trying to recharge flat batteries and run the load at the same time.

The CEMF cell is used to drop the output voltage of the power plant slightly. In a nominal 48V system, the voltage is actually 52V to meet the requirements of the batteries. Most modern DC powered equipment has a wide input voltage range so CEMF cells are very uncommon in today’s DC power plants.

The next component in the system is the battery distribution and fuse bay (BDFB). The BDFB splits a large capacity feed from the DC power plant into a number of smaller feeds to the rack and cabinet level panels. The BDFB usually contains the largest fuses or breakers in the system and connects to the data center’s audible and visual alarms to alert data center staff to a blown fuse or tripped breaker.

Finally, we have the rack and cabinet level fuse or breaker panels. These split the larger feed from the BDFB into smaller feeds to the individual equipment. These panels usually contain the largest number and smallest size of fuses or breakers. As with the BDFB, the rack and cabinet level panels connect to the data center’s audible and visual alarms to alert data center staff to a blown fuse or tripped breaker.

This gives a brief overview of the data center DC power plant. In a follow up post, I’ll provide some tips on how to make sure your green data center DC power plant is as green as it can possibly be!

Vern, SwiftWater Telecom

data center, web hosting, Internet engineering

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