Which two transformer configurations are commonly used in large-scale data centres?

Delta-Wye (Δ-Y) and Delta-Delta (Δ-Δ) are two common three-phase transformer configurations in large data centers. The Delta-Wye is the most prevalent for the main service entrance transformer, stepping down medium voltage to low voltage (e.g., 480/277V). Its delta-connected primary is robust against harmonic currents, and the wye-connected secondary provides a necessary neutral connection for single-phase loads. Delta-Delta configurations are also used, often for isolation transformers or to power specific loads that do not require a neutral, offering good performance with unbalanced loads.

B. Wye-Wye configurations are generally avoided for main distribution due to potential instability and harmonic issues unless a stabilizing tertiary delta winding is included.
D. Series-Parallel describes a method for connecting circuit components (like cells in a battery), not a type of three-phase transformer winding configuration.

1. Avelar, V., & Azevedo, D. (2012). White Paper 153: Single Phase vs. Three Phase Power Distribution for Data Centers. Schneider Electric. p. 5. (Discusses the use of Delta-Wye transformers to create the 480/277V and 208/120V systems common in North American data centers).

2. Das, J. C. (2015). Power System Analysis: Short-Circuit, Load Flow, and Harmonics. CRC Press. Chapter 7, "Three-Phase Transformer Connections." (This academic text details the applications and characteristics of various configurations, confirming the utility of both Delta-Wye and Delta-Delta in industrial and commercial power systems like data centers). DOI: https://doi.org/10.1201/b18402