Critical systems: Power backup

Crossed wires shorting out, Troy, Illinois. Af...Image via Wikipedia

Obviously, an ISP doesn’t function without electricity, so we’ve got big investments in redundant power here.

A datacenter power system consists of multiple inputs which are arbitrated by a transfer switch, and multiple loads such as UPS systems and air conditioners (CRACs).

The primary input is PG&E, and the transfer switch monitors the quality of this input. If the utility power goes offline or fades, the transfer switch sends a signal to the starter on the generator, which powers up automatically. Once the generator power output is online and stable, which typically takes twenty to thirty seconds, the transfer switch physically swings a huge set of contacts over to the new input, transferring the load.

The UPS systems and their batteries carry the datacenter computing load during this startup and transfer, while CRAC loads are dropped during the transition. A datacenter can’t function for long without cooling, so the entire generator and transfer switch system must function as designed in order to stay online.

The generator itself is the really cool bit of this whole setup. For those who are into engines, it’s a 24 liter V-12 Detroit Diesel, with twin turbochargers. That’s a full two liters of per cylinder – imagine a piston and cylinder the size of a 2 liter soda bottle. Now, gang up twelve of them. It’s a huge engine. At full throttle it generates over one thousand horsepower, and three quarters of a megawatt of power.

In our five years at our Apollo Way location, the generator has only been called on to respond to a power outage twice. PG&E has done a great job for us, delivering quite reliable power. But, we still must test fire the generator once every week, top up it’s fuel every few months, and trade out old fuel for new periodically. It’s full generating capacity is totally load tested every few years by hooking it up to a massive resistor/heater bank. The maintenance and load testing is critical to assure that the power will be there when we do need it.

Reblog this post [with Zemanta]