Effects of phase imbalance on data center energy management

Abstract

Phase imbalance has been considered as a source of inefficiency in the data center that causes energy loss due to line impedance and increases reactive power. Strategies assume high loss due to phase imbalance and propose sophisticated energy management algorithms including phase balance aware workload scheduling algorithm and dynamic power distribution unit assignment to servers. However, such attempts do not utilize an objective measure of the inefficiencies due to phase imbalance to evaluate the significance of their contributions. Excessive imbalance in a three phase load has various undesirable effects. This paper, first objectively characterizes the inefficiencies due to phase imbalance and then provides numerical measures of the losses in realistic data center deployments. Phase imbalanced load in a delta configuration results in reduced power factor, which is undesirable for several reasons. Also, an imbalanced load (both in delta or star configuration), results in higher line currents, leading to higher line loss. However, this increase in loss is a fraction of a percentage of the energy consumed. The paper also discusses effects of work load scheduling on phase imbalance, and how to minimize the same.