This morning I was reading about preventing cascading failures in the data centervia power load balancing. I’ve written previously about not allowing data center failures to get out of control and cascade into a much larger event, in this post I’ll be talking a little bit about the importance of power balancing.
At the simplest, power load balancing is just what it says. Power loads should be balanced at distribution points such as breakers and balanced across redundant feeds to equipment. This insures that a configuration that works fine under normal conditions doesn’t overload and trip in failover conditions. Beyond the obvious of making sure that the power configuration will reliably work under all load conditions, there are also power quality issues as well.
Most industrial/commercial locations are supplied by 3 phase AC power in either a delta or wye configuration, 3 hot phases, and 1 neutral (wye only). Single phase equipment is supplied from either 1 hot phase and the neutral or 2 hot phases. The issue will this type of power is that load imbalance of more than 10% between the hot phases can cause significant misbehavior of the transformer not to mention efficiency problems as well. We just had a landlord correct a load 3 phase load balancing issue at one of our facilities, 95% of the distribution load was on 1 phase of the breaker. This imbalance caused what should have been 120VAC to drop as low as 100VAC.
So where does data center DC power enter into this? A modern modular DC power plant collapses the 3 phase power into one DC power feed. Since the rectifier modules operate in parallel, the load on each AC circuit will be perfectly divided between them. Compare this to AC powering equipment where the load of the equipment is constantly changing, meaning that you could never balance this type of load with any precision. With a DC power plant, as long as you run modules in multiples of 3, you’re guaranteed to maintain perfect load balance.
Efficient in operation, efficient in use of your AC power capacity, making the power balancing act look easy, DC power is the choice for the green data center.